Thread for discussing plasma physics topics:>General plasma-related questions>Recent papers and developments>Fusion plasmas>Astrophysical plasmas>Low temperature and atmospheric plasmas>Complex/dusty plasmas>Plasma generation and processing>Plasma instrumentation and diagnostics>etc.
Useful Resources (WIP):General Plasma Physics>Chen, F. Introduction to Plasma Physics and Controlled Fusion>10.1007/978-1-4757-5595-4>Bellan, P.M. Fundamentals of Plasma Physics>10.1017/CBO9780511807183>Conrads, H. & Schmidt, M. Plasma generation and plasma sources>10.1088/0963-0252/9/4/301>Braithwaite, N. Introduction to Gas Discharges>10.1088/0963-0252/9/4/307>Piel, A. Plasma Physics: An Introduction to Laboratory, Space, and Fusion Plasmas>10.1007/978-3-642-10491-6>Gurnett, D. Introduction to Plasma Physics: With Space and Laboratory Applications>10.1017/9781139226059Fusion>Freidberg, J. Ideal magnetohydrodynamic theory of magnetic fusion systems>10.1103/RevModPhys.54.801>Freidberg, J. Ideal MHD>10.1017/CBO9780511795046Space Plasmas>Baumjohann, W.B. & Treumann, R.A. Basic Space Plasma Physics>doi.org/10.1142/12771>Treumann, R.A. & Baumjohann, W.B. Advanced Space Plasma Physics>10.1142/p020>Tsurutani, B., et al. Space Plasma Physics: A Review>10.1109/TPS.2022.3208906Low Temp., Atmospheric, and Complex Plasmas>Lichtenberg, A. & Lieberman, M.. Principles of Plasma Discharges and Material Processing>10.1002/0471724254>Kong, MG., et al. Plasma medicine: An Introductory Review>10.1088/1367-2630/11/11/115012>Misra, N.N., Schlüter, O., & Cullen, P.J. Cold Plasma in Food and Agriculture>10.1016/C2014-0-00009-3>Merlino, R. Dusty plasmas: from Saturn’s rings to semiconductor processing devices>10.1080/23746149.2021.1873859>Shukla, P. & Mamun, A. Introduction to Dusty Plasma Physics>10.1088/0741-3335/44/3/701Instrumentation and Diagnostics:>Hutchinson, I.H. Principles of Plasma Diagnostics>10.1017/CBO9780511613630>Merlino, R. Understanding Langmuir probe current-voltage characteristics>10.1119/1.2772282>Hershkowitz, N. & Kim, Y.C. Probing plasmas with ion acoustic waves>10.1088/0963-0252/18/1/014018>McWilliams, R. & Edrich, D. Laser-induced fluorescence diagnosis of plasma processing sources>10.1016/S0040-6090(03)00358-4
For me, it's plasma windows
>>16233485That's where they use plasma layer to shield a target from an accelerator beam, right? Haven't read a lot of research on them - any literature you can share?
>>16233749That's exactly it>any literature you can share?I wish - I'm just a plasma neophyte. I've had trouble finding if plasma windows ever went beyond the patent. Excellent literature list, I'll have a look through it.
>>16234159>>16233749Just adding to that the plasma window claim is that high temperature plasma can be very viscous, enough so that it can hold back a full atmosphere of pressure, such as an access wall into a vacuum chamber. Yet rarified enough that instruments can be passed through without damage.I'd love to confirm this high viscosity is actually true because it seems like a most interesting property.
>>16234159There’s a decent amount of literature https://scholar.google.com/scholar?hl=en&as_sdt=80000005&sciodt=0%2C23&cites=2594790500051944381&scipsc=1&q=window&btnG=Here’s the final report https://www.osti.gov/biblio/973598 it looks like it didn’t ever achieve great welding speeds and it wasn’t very cost competitive.>>16234166It’s not the viscosity. The pressure of the plasma is equal to the pressure of the ambient air, but since p=nkT the density is much lower since he temperature is 50x higher (also ~1 eV is pretty cold for a plasma). https://pubs.aip.org/aip/pop/article/5/5/2130/1069026/A-plasma-window-for-transmission-of-particle-beams He doesn’t even bother to calculate the viscosity in his paper and acknowledges that the model he uses isn’t even valid in this parameter space, but based on fits to MD data the viscosity in a thermal arc is around 10^-4 to 10^-3 Pa-s which is in between air and water.
>>16234159>>16234166Did some digging and found the original paper from the team at BNL on developing a plasma window. Looks like in their original experiment they succeeded in using a plasma window to maintain a moderate vacuum pressure; a roughing pump alone was able to maintain a pressure differential of 80 Torr inside the chamber vs 760 Torr outside, while the roughing pump in combination with the plasma window allowed the interior to get down to 350 *milli*torr. That's an improvement of more than two orders of magnitude and is bordering on pressures you could maintain a stable glow discharge or electron beam at (low temp discharges, for sure, can operate at a few hundred mTorr, e-beams I'm less sure about, you might need to get down to a few mTorr that). Though it's worth pointing out they had to pump 50 amps into that sucker to get it to operate, so the bulk of the apparatus looks to be dedicated to cooling.It does seem to imply that the effectiveness of the window is due to some kind of viscosity effect. Hershcovitch cites a review paper from the 60s on plasma transport that suggests the collisional effects result in a viscosity approximately linear to plasma temperature, but I don't know how accurate that is (might look up the transport paper later).He also suggests the use of plasma windows in plasma welding applications, but I think modern plasma welders opt for just using gasses like helium and argon and just pumping a high enough discharge voltage into them. It does sound like they might be using the technique on some of the experiments at CERN now.
>>16234626>>16234631Good finds!
I posted picrel on /k/ a while ago, asking if putting a De Laval nozzle on a plasma cutter might be able to generate long-range plasma channels with relative stability in air. what u guys think?>tfw /k/ bans u for the weekend because a thread on stopping artillery fire with tile and sandbags is somehow "not weapons/armor">Verification not required.
>>16235132Hmm, in air? Probably not. You could use a nozzle to get a fairly stream of neutral gas and try to ionize that, like they do with CAP jets, but the range is mostly limited by the plasma generating conditions.
>>16235419what if you had the plasma flowing parallel/through a bunch of thin-ass copper wires, so molten copper particles are ejected in the jet? might this improve distance?
>>16235132How does this compare to how plasma cutters normally work??
>>16235738normally, plasma forms *OUTSIDE* the nozzle, rather than inside it, so the nozzle does not accelerate the plasma
>>16235738It *is* how some of them work. You have a nontransferred arc which is pushed out of the AK gap by the gas flow, and the opening can already expel the heated gas at supersonic velocities.
Which does /sci/ prefer? RF or DC?
Worst thread on sci rn fr fr
>>16236032Not surprised they need water cooling for those. They're probably running, what? 20-30 amps? Couple hundred volts?>>16236256DC is the patrician choice>don't need an expensive RF source>don't need a complicated matching network>don't need to compensate all your instruments>don't need to deal with waves from your source interfering with shitAs long as you can find a moderate high voltage source and can current limit it for a stable glow discharge you're gold
i'm not well-versed in electromagnetics - can somebody explain to me how in the hell the magnetic field lines in a Birkeland current are parallel to the current flow?
>>16236584The parallel magnetic field isn't generated by the Birkeland current, it's generated by currents in the Earth's core. As for why there's net current instead of cancelling out, it's because the electrons gyrating around the earth's magnetic field lines experience a magnetic mirror effect when they get close to the poles, since the magnetic field gets stronger closer to the Earth's surface.There's also current perpendicular to the field lines caused by gradient drift effects.
>>16236686This, you basically always have *some* amount of currents, wave propagation, diffusion, etc. that is parallel to the field, *and* some amount perpendicular to it.
>>16233254Look at the ITER youtube channel they got some cool stuff there.
>>16233254Is plasma temperature proportional to excitation frequency? What parameters change when you vary the RF source frequency for ICP/CCP?
>>16237321In low-temp plasmas, electron temperature is determined by the balance between ion generation at your electrodes versus ion loss to walls and pumps, so weirdly the physical volume of the chamber and your volume pumping rate set the electron temperature. Ion temperature is largely determined by your neutral gas pressure and your ionization rate - the more neutrals you have, the more likely your ions are just going to equalize at about room temperature from collisions with the neutrals. Ion density is determined by the power balance in the plasma generation, so for a fixed voltage (which is necessary for stable discharges) your density is basically proportional to current. To the best of my knowledge, RF source frequency has no impact on the plasma parameters. The frequencies are just chosen to avoid conflict with communication and data frequenciesNow if you're talking about fusion plasmas, that could be another matter - I'm not as familiar with those, and I know they have a whole mess of different heating mechanisms and other shit going on.
>>16237344Thanks for the answer. Yes, I was asking about cold plasma, like in sputtering or etching machines.So temperature is literally determined by how much power you can vomit into the chamber. I had heard some talk about different plasma behaviors at different excitation frequencies. It was in the context of plasma etching and surface damage, so probably it has to do with some chemical-plasma-magic shit.
>>16237352Electron temperature is mostly determined by chamber geometry and pumping rate.Ion temperature is mostly determined by neutral pressure and ionization rate.Plasma density is mostly determined by power.I imagine some of these conditions could have some weak frequency dependence (possibly ionization rate or density), and I could certainly one or more plasma processing methods having some dependence on frequency as well. L&L's Principles of Plasma Discharges and Material Processing might have some details on that sort of thing, might be a good source to look up >>16233256
>>16237352IIRC, RF frequency is important for etching - with the speed and quality of the etching being proportional and inversely proportional (respectively) to the RF frequency. So like, if you’re generating a plasma with a frequency in the kHz band, you get high quality etching but it takes longer, whereas if you’re generating in the GHz band it’s much faster but much poorer quality. This is, I believe, why the 13.56 MHz frequency is so popular for etching. It’s an approved frequency for RF generation that also gets you a good balance between quality and speed in etching processes. I don’t have a source handy, that’s just what I can vaguely recall from one of my plasma courses in grad school.Not sure about how things like surface treatment or deposition depend on frequency though.
>>16237790You're mixing up two different things, in ICP plasma processing, you typically have two separate RF sources - one to sustain the plasma, and one to control implantation to the substrate. Frequencies in the 10s of MHz are good because in an unmagentized plasma, you get efficient energy transfer to the plasma when the RF frequency is approximately equal to the electron-neutral collision frequency. There are ECR heating sources in the GHz range for magnetized plasmas.I doubt you'd even get any advantage over a DC source for breakdown at KHz since the field would be pointed in the same direction for such a long time relative to electron transit times. It's typically the bias applied to the wafer in order to control the acceleration of ions across the sheath for implantation.
>>16237790>>16237930Also the 13.56 MHz source is also usually pulsed at a few KHz because it's better at exciting high threshold reactions from the initial spike in temperature when all of the power is deposited in a small population of electrons. So you can get higher densities of reactive species compared to what you'd get at the steady state electron temperature which is essentially indepenent of power.
>>16237930>typically have two separate RF sources - one to sustain the plasma, and one to control implantation to the substrateReally? Interesting, I’d always assumed it was one source. Could you elaborate on the role of the second source?>>16237962>the 13.56 MHz source is also usually pulsed at a few KHzPulsed as in actually switching on and off or more of a polarity-switching kind of pulsing?
>>16238028The first power supply sustains the bulk plasma, and therefore determines the total ion flux, while the second controls the sheath voltage, which accelerates the ions onto the substrate. It's important to have independent control of the flux and ion energies, espeically for semiconductor applications where you're trying to etch something in a deep channel and want you reduce the angular spread of the incident ions.And yes, you switch the RF source on and off
>>16238105Very interesting! Thanks! Any good sources you can recommend for learning more about processing?
>>16238160There aren’t really any comprehensive up to date resources out there. The course I took just used a packet of 500 pages of the professor’s handwritten notes with a bunch of excerpts mixed in.Besides Lieberman’s book, some good ones are “Plasma Chemistry” by Fridman“Handbook of Sputter Deposition Technology” by Wasa, Kanno, Kotera and Andrew
>>16238230>The course I took just used a packet of 500 pages of the professor’s handwritten notes with a bunch of excerpts mixed in.that sounds like it could either be the best or the worst course experience imaginable, with nothing in between
>>16238295NTA, but similar experiences. It’s very hot or miss. Had a fluid dynamics course where the prof used his own notes and it was one of the best courses I’d ever taken, and an electrodynamics course sequence that did the same thing and it was a fucking nightmare - two semesters of hell.Really depends on the prof.
i dont know shit about plasma but ill bump any thread thats actually science. rock on, bros.
>>16238846>i dont know shit about plasmaWhat would you like to know?
Is it feasible to develop a simple plasma experiment on a small budget (say $1-2k)? Not like a fusor or high quality research apparatus or anything like that (I know stuff like that costs tens or hundreds of thousands of dollars to manufacture), but just something that could make a basic argon or even air plasma and get some simple probe measurements from.My school doesn't have anyone who does plasma physics or fabrication and I'm interested in trying to develop some practical experience on my own, maybe save up this Summer to try finding some second-hand or surplus parts. Just how big is the funding gap between something that can make a pretty glow for a classroom demo and something you could get real (but basic) data from?
>>16239982It definitely depends on what you want to do, but you'll have a hard time even finding a used vacuum pump in that price range, most equipment of extremely expensive. I've spent around $15k in the past month on shit even though we're already well equipped.
>>16239982Can you build something that will make a plasma? Yes.Can you build something decent enough to do actual research (even amateur stuff)? I'm gonna have to say 'no'.A lot of your core equipment is REALLY expensive. Some things you can get cheap if you're willing to hunt surplus auctions or scope out a university's dumpsters during excess season, but a lot you can't get cheap, even second-hand.Vacuum chambers - you can usually get some good deals here if you're buying second-hand. You could find a lot of KF-40 pieces for a couple hundred bucks, I've even snagged a few ISO-100 pieces in that price range, but once you factor in a main chamber and all the caps, seals, clamps, valves, etc. you're looking at at least a grand. If you're okay with an air plasma you don't need to worry about gas pressure regulation, but if not, gas tanks aren't cheap anymore and regulators are pricy too.Vacuum pumps - like >>16240180 said, don't come cheap. You can get a little Harbor Freight pump for $100, but you won't be getting any kind of base pressure under a few hundred mTorr. A good rotary valve or dry scroll pump, used, is at least one or two grand.Power - if you're desperate, I've actually had really good luck adapting the innards of plasma arc lighters to make a cheap and dirty high voltage supplies for classroom demos, but this won't make a stable plasma you can do measurements with. A current-limited HV supply, even used, is gonna be at least grand. More for an RF supply and matching network.Instrumentation - you can build a probe for a few bucks, but the hardware to run and analyze data from it is fuckoff expensive. A source meter is a couple grand, same for an oscilloscope, you can get away with a power supply and a multimeter, but that's still several hundred bucks and it'll take you an hour to do a single probe trace.
I'm interested in wakefield acceleration, is there any recent news or is the technology dead?Can plasma accelerators be used for muon acceleration? For free electron lasers using plasma acceleration, could the undulator and plasma accelerator be combined into a more compact device?
>>16241270It’s not dead, there’s still a lot of interest in it. The ZEUS laser facility opened a few months ago and they have a wakefield accelerator group, so there should be some cool work coming out of there soon.I doubt they could really be used for muon acceleration, it’s very hard to do externally injected bunches since the tolerance you need in momentum spread to get the particles trapped in the accelerating phase is so tight. There was a PoP paper on it recently https://pubs.aip.org/aip/pop/article/31/2/023109/3267711 but it’s only a simulation so it doesn’t mean much.Wakefield accelerators are already so small compared to the undulator that there wouldn’t really be a benefit to combining them. None of the existing setups do it since their accelerating region is only a few cm long https://www.nature.com/articles/s41586-021-03678-xhttps://www.nature.com/articles/s41586-022-04589-1https://www.nature.com/articles/s41566-022-01104-w
>>16241270>>16241814Also the material for the most recent USPAS courses on wakefield acceleration are available https://sites.google.com/umich.edu/uspas-plasma-accelerators/homehttps://sites.google.com/view/uspas-particle-driven-pwfa/homeIt’s annoying that nobody has managed to put together a decent monograph on the subject yet.
>>16239348what separates a gas from a plasma? i have a decent background in solid-state physics here fyi.
>>16241839As in what's the difference between the two? Ionization.As soon as you pluck off electrons and add charge separation into the mix the dynamics of the system completely shift. You go from all the thermal and fluid behaviors of a hot gas to suddenly throwing in electric and magnetic fields and waves, Debye shielding of surfaces, dielectric properties, filamentation behavior, etc. etc. etc.To put it in solid-state terms, it's like the difference between a neutral solid and a semi-conductive solid - that tiny little change from combining the right types of materials completely alters the dynamic behavior of a whole class of matter.
>>16241864i was more looking for a description involving electron states. for example, at room temperature, silicon (or really any semiconductor) stochastically sheds some of its electrons to higher energy states due to heat, which are then free to migrate, but you wouldnt call that a plasma. in my head, im imagining a plasma is characterized by a departure from (net) neutral molecules (atoms?) flying around, and instead positive ions and electrons are now flying around. am i on the right track?>it's like the difference between a neutral solid and a semi-conductive solidthose, uh, arent mutually exclusive, but i appreciate the effort fren <3
>>16241885I would argue that the conduction band electrons actually are very close to a plasma. The high frequency optical properties of metal are actually identical to that of a plasma with a stationary ion background.Plasmas are net neutral* and most plasma phenomena is actually caused by space charge induced electric fields which attempt to return thr plasma locally to charge neutrality when perturbed from equilibrium.The main difference between the kind of coulomb interactions you see in a metal and a plasma is that for both ions and electrons, the coupling constant [math] \Gamma=\frac{\Phi(a)}{k_B T} \ll 1 [/math] or the potential energy evaluated at the average inter-particle spacing is much less than the thermal energy. This means that rather than being trapped in a potential well interacting only with its nearest neighbors, particles in a plasma are effectively free moving, with their motion being governed by collective phenomena involving interactions between a large number of particles.* technically most confined plasmas have a relative difference between ion and electron densities of about 10^-6 since there needs to be a small positive charge to prevent all of the faster moving electrons from just being absorbed by the chamber wall
>>16241961any famous experiments in the early history of plasma physics?
>>16241961Using coupling parameters to quantify if something is a plasma or not is an okay starting place... but it gets messy when you consider the existence of strongly-coupled plasmas (where Γ~1) or complex plasmas (where the coupling behavior of the microparticles can run from Γ<<1 to Γ>>1 depending on the the conditions of the background electrons and ions).
>>16242688That's true but almost all books will include the low coupling strength (or the equivalent formulation in terms of number of particles in a Debye sphere) as part of the definition of a plasma, and most of plasma theory does not hold in the strong coupling case.You lose a meaningful concept of Debye shielding, and basically all wave interactions change dramatically since the random phase approximation no longer holds. You basically have to completely rederive everything starting from the Liouville equation and the BBGKY hierarchy and it ends up looking more like the theory of liquids than traditional plasma physics. So you end up with totally different transport and thermodynamic properties and can't even formulate a coherent strongly coupled version of MHD since Onsager reciprocal relations break down
>>16242197NTA but the earliest plasma physics stuff is probably characterization of electrostatic discharges, and wouldn't have been considered "plasma physics" at the time.
>>16242197Farnsworth's fusor experiments in the 60s maybe?
>>16242744True. It’s one of the more frustrating and fascinating things about plasmas - as we’ve learned and experimented, the range of temperatures, densities, coupling parameters, ionization fractions, degrees of quasineutrality, etc. of what we might consider a plasma has expanded beyond all of the original definitions, and about the only thing they still have in common is that some amount of the fluid reacts electromagnetically. It’s crazy to think that such a broad parameter space exhibits so many common behaviors.
>>16241270It's not dead, but it's a long way from producing viable results with more massive particles like muons. To my knowledge it's never been successfully demonstrated on anything heavier than an electron. All they have for muons so far is some very basic simulation results.
>>16242197This book discusses some of the early fusion experiments, going all the way back to the first magnetic mirror fusor attempts in the 30s, and then transitioning into the steady improvements in the 60s and 70s up through the modern era.
>>16233254Why? do you want to build a useful fusion reactor?
>>16233254>Boozer coordinates>has nothing to do with the drunkard's walk
I'm really bored, and I was reading a research paper I liked. I looked at the code used for the simulations, and it's absolutely disgusting. How receptive would you guys be to someone reaching out with a refactored version of your code? I mean, this is a 1000+ lines with no comments, everything in one file, numerical methods written where things aren't saved and are recalculated every time, basically everything that you shouldn't do, this guy's done.
>>16245545Pube.
>>16245547nta but what's the problem with doing this? i get comments, suggestions, corrections on my papers via email
>>16245579>what's the problemIf it's worth the pixels it's written in, it's free game.And that's a pretty big if in current year
>>16245547>>16245579I'm not sure what the issue is. This would be completely standard if it were ever posted somewhere like github. Even boomers shouldn't be taking offence to that.
>>16245579If it’s done tastefully and respectfully I don’t see the problem. But you also don’t wanna be going “bruh your code sucks you shoulda done it like I woulda”.
>>16245724But if he did it would probably be better, it's just that it wouldn't be his anymore... or hers, whatever
>>16245545>>16245724Yeah I meant as in "hey I liked your papers and implemented your thing on my machine, i think this version of your code should be faster and easier to read" kind of thing. And if I put it on github I'd obviously give all credit to the original papers and authors. I also think it would make their papers more accessible to others.
>>16245727Constructive criticism is best done a little bit at a time. If some inexperienced artist posts their first attempt at a portrait you don’t immediately tear down every single aspect of their attempt and then post an expertly made version of their drawing as a rebuttal. You tell them one or two things to try differently - ‘work on your perspective drawing’ or ‘the hands need work, keep practicing’.Pick one or two things to focus on on your comments to them (like the lack of commenting or suggesting an alternate numerical method or whatever) instead of rewriting their entire code.It’s about pointing out a few manageable things someone can and should improve on and then giving them the opportunity to do so before dumping more critiques.
>>16245735Last time I checked, this place was not what I would call constructive. It can be but it's usually not, at least not in any conventional way.Fortune favors the bold. Post Code.
>>16242688What exactly am I looking at here? I mean, I can read the filename, but I need some context.
>>16245805When you have dust or other small particles in a plasma, they charge up from incident electron flux to a few thousand e. This causes them to electrostatically levitate above the electrode in a 2D layer. The large charge causes the dust particles to be in the strongly coupled regime where they are trapped in potential wells of surrouding dust particles, and form a crystal structure.https://www.tandfonline.com/doi/full/10.1080/23746149.2021.1873859
>>1624554590% of the time this stuff goes under a CC license for a reason. Just do it. If the author complains about someone showing interest in his work then fuck him.
>>16242857>>16243227>>16245069thanks frens <3
>>16245805Adding to >>16245964 's post: In this case a monolayer is formed because (a) the particles are all generally about the same size/charge/mass and (b) the radial component of the electric field is negligible in the area where the cloud has settled (it probably increases sharply a little passed the edge of the monolayer). In more parabolic trapping potentials you'll often see spherical or conical clouds of particles form (although you'll usually only be able to see a single sheet of it illuminated at a time). Biased surfaces or gradients in plasma density can also lead to the formation of void-like structures in the clouds (webm related)The coupling parameter of the particles can actually cover a pretty substantial range, from solid-like to fluid-like to gas-like behaviors; though the strongly-coupled solid-like regimes tend to be of the most interest because they usually exhibit a lot of features that can be used as analogs for crystals and soft-body physics. The dust can also exhibit different oscillations like acoustic waves (again, webm related), collective ExB drift rotation, or so-called 'breathing modes'.
>>16233256Since it came up, here are some resources for numerical methods in plasma physics, mostly focused on PIC and MHD. I have a few more on MD (including tree methods), but this is already getting pretty long.>Birdsall, C. K. & Langdon, A. B. Plasma Physics via Computer Simulation>10.1201/9781315275048>Tajima, T. Computational Plasma Physics>10.1201/9780429501470>Jardin, S. Computational Methods in Plasma Physics >10.1201/ebk1439810958>Eastwood, J. & Hockney, R. Computer Simulation Using Particles>10.1201/9780367806934>Dnestrovskii, Y. & Kostomarov, D. Numerical Simulation of Plasmas >10.1007/978-3-642-82592-7>Drobot, A. Computer Applications in Plasma Science and Engineering >10.1007/978-1-4612-3092-2
>>16247263Something I've always wondered about with computational plasma physics: How big of a problem is the difference in dynamic timescales? I haven't gone too far down the rabbit hole of simulating plasma behaviors, but it's always seemed to me like the only way to feasibly simulate seconds or minutes of plasma behavior would be to *drastically* oversimplify the physical models.
>>16247943Pretty much, you have to pick a timescale, MHD, langmuir, etc., and work with that. No simulating everything moment by moment>>16247263>Dnestrovskii, Y. & Kostomarov, D. Numerical Simulation of Plasmas >10.1007/978-3-642-82592-7Oooo new book>tokamaksffs, sfs z-pinches are the future
When I get my workshop up and running I want to try building an electrolaser
>>16248663for me, it's screw pinch
>>16248663Tokomak books will help, since pretty much all Z-pinch codes are just resistive MHD + radhydro.I doubt you'll ever see a dedicated Z-pinch book soon since a lot of the codes are slightly modified nuclear weapon simulators and getting papers and conference presentations past the censors to make sure there isn't anything export controlled or classified in them is already a huge pain in the ass, to say nothing of an entire book. There is quite a bit on radiation hydrodynamics simulations in both Mihalas&Mihalas and Castor's books. And there are a decent number of astrophysical codes that people also use for Z-pincheshttps://github.com/sseyler/HERMESHDhttps://github.com/PrincetonUniversity/athenahttps://flash.rochester.edu/site/flashcode.htmlBut honestly you can get pretty far with just the 1-D SAMM model https://pubs.aip.org/aip/pop/article/23/1/012705/108462 which you can write in a day.
>>16248663>>16249311>>16249321What's with all the renewed interest in pinches lately? I keep seeing them brought up everywhere nowadays. I thought those were all pretty much ruled out as viable design for fusion decades ago.
>>16249399the "non-viability" of pinch fusion development is basically explained by the unfortunate coincidence that pinches hit the (still intractable for all fusion tech besides ICF) instability problems right around the time tokamaks were revealed to reach surprisingly high plasma temps, and everyone essentially shifted focus to Big Donut (tm).of course, looking back, the abandonment of pinch fusion experiments was not actually as well-justified as was thought at the time, especially since tokamaks have run into similar instability problems anyway - turns out this shit is just how plasma do.as it stands, pinch fusion experimental research has basically been in quasi-stasis until very recently, a fate it somewhat shares with everything except tokamaks and ICF, the latter of which has both the only successful experimental net energy fusion results (which it has had since the first H-bombs; NIF's breakthrough of scaling that down to laboratory scale is still super important, though) and a rather straightforward combination with z-pinches in the form of MagLIF.while not at modern tokamak level yet, it should be noted that MagLIF is well ahead of early tokamak results in just a few years of research. it may plateau at a similar place to where tokamaks are currently struggling, but it has gotten staggeringly far without much funding, focus, or time, and more generally the ability to sidestep magnetic confinement instability with an inertial confinement component appears to be a viable strategy. it's unfortunately not a strategy purely MCF systems can replicate (you can add MCF properties to ICF designs, but not ICF properties to MCF designs nearly as easily), so it's actually most closely dependent on ICF research, which means that a) tokamak true believers are dismissive of MagLIF and NIF's ICF results because apparently they're a bunch of immature, jealous children and b) the research has a higher probability of getting muzzled for classified defense reasons.
>>16249508>a rather straightforward combination with z-pinches in the form of MagLIFCan you elaborate a little more on MagLIF? I'm more of an LTP guy so the only LIF I'm familiar with is laser-induced fluoroscopy.>the research has a higher probability of getting muzzled for classified defense reasonsThat doesn't surprise me, sadly.
>>16249531Magnetized Liner Inertial Fusion. It's a Z-pinch concept that adds an applied axial magnetic field for better confinement of the fuel and laser preheatinghttps://iopscience.iop.org/article/10.1088/1741-4326/ac2dbe/meta
>>16249311I cannot agree with you because screw-pinches do not do away with the need for external magnets in order to achieve confinement, like the SFS Z-pinch does.>>16249321Thanks for the pointers, anon>>16249399Z-pinch got stabilized in the mid-90s by Uri Shumlak using a shear-flow mechanism, proof-of-concept developed in the mid-2000s, and now he has a company, Zap Energy, which has received $100m's of funding to develop. The pulsed power system needs to run at 10Hz with 1 MA peak current delivered to seed plasma so that's the main difficulty.
>>16249531https://en.wikipedia.org/wiki/Magnetized_liner_inertial_fusionmy understanding is basically you z-pinch a liner full of preheated plasma so much it inertially compresses the plasma inside of it to fusion, instead of directly z-pinching the plasma in a vacuum.interestingly, according to https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.125.155002, the best results appear to always be from increasing both the inertial and magnetic confinement, which does suggest that neither is dominant and should be focused on exclusively, at least for these designs. TL;DR: combination isn't a waste of time
Can someone redpill me on Wendelstein 7-X at the Max Planck institute ? Was told to me they're making extreme headway in steady state operations for magnetic containment
>>16249821From what I've heard from grad students working on collaborations with W7X it's going pretty well. They smashed the previous stellarator record for triple product by something like 50% during OP1. They started OP2 last year, which means they should be making stable discharges in excess of half an hour by now.There's been a surprising resurgence in interest in stellarators in recent years. I hear PPPL is actually trying to build one using mostly off-the-shelf parts and permanent magnets.
What software works for roughly simulating ion movement in electric fields, the kind of problem you encounter in fusors. I don't want to drop fuck tons of money on SimIon, but I can program well enough to write glue code so I hope to be using some open source project to simulate my thing
>>16249974I mean, you can write up a pretty basic code in pretty much any language. The only real bottleneck is memory and computational power.
>>16250018I did find and adapt some code for doing ion movement and it has been working ok for useless toy examples but how do I generate it an electric field that would be produced by different configurations of electrodes?
>>16250027Sounds like a boundary value problem, anon. You'd need to figure out a way of defining the boundary values set by your electrodes and the chamber wall and then iteratively calculate your ion behavior.
>>16250051 I feel like am kind of in over my head trying to simulate shit already, where would I at least learn how to make a solver for that?
>>16249607>screw-pinches do not do away with the need for external magnets one thing i've often wondered about discharge systems like SFS Z-pinch machines is if they wouldn't be more efficient with an external magnet anyway. the magnet being external isn't technically the issue with most MCF, the issue is the ludicrous field strengths required. since SFS Z-pinch machines can allegedly self-stabilize based on 2D simulations (i've never seen a paper with a 3D one), it seems to me that you could lower the other requirements with more easily achieved external magnetic fields, and the resulting total device would be more efficient. that's just conjecture, though.SFS looks very, very similar to a dense plasma focus, something that's largely been abandoned for fusion because it doesn't scale well at all, despite being very experimentally accessible compared to something like a tokamak or stellarator (so accessible in fact that it's apparently used as a fusion demonstrator or electrically driven neutron source, like fusors are).Zap Energy has a suspiciously strongly marketed online presence whenever you search "shear flow stabilized", and they've made some rather dubious claims, and the fact they're using something that looks a lot like a system from the 1960s and calling it something else... all just reminds me of Helion. because if you were curious, that's exactly what Helion's been doing with "field reversed configuration," which was often historically just called a "spheromak" before CTFusion pioneered the modern venture capital fusion grift in the mid-2010s, renaming their spheromak design a "dynomak" with a "compact toroid" (hence "CT"). their design never worked. Helion's design is basically a linear spheromak injector/collider, which have been around in designs for decades.CTFusion shut down in 2023. apparently... 3/4 of the founders went to Zap Energy. despite that being a completely different fusion design.really makes ya think.
>>16250054From everything I can read it seems like Commonwealth is the least full of shit. Just a tokamak, with advanced superconductor coils for higher magnetic field
>>16250054>the magnet being external isn't technically the issue with most MCF, the issue is the ludicrous field strengths required.Cool, two sentences in and we're already being meaninglessly pedantic. >since SFS Z-pinch machines can allegedly self-stabilize based on 2D simulationsROFL, it's been known since the mid-2000s that shear-flow stabilization is real, and has been demonstrated experimentally.>really makes ya thinkYour post has made me think you're an idiot
>>16250053Kinetic aspect: Research the PIC algorithmEM aspect: Research Maxwell solvers In the case of the electrode BCs: you will need to specify them explicitly. Their surface area is represented by some subset of the mesh. On these gridpoints you specify the appropriate values based on what the variables in the problem should be.
>>16250054>>16250067something particularly dubious to me about Zap Energy is the fact that DPF fusion is the design that Eric Lerner's LPPFusion company has been working on since BEFORE 2010, and while Lerner has said plenty of things i'm extremely skeptical of... with him, i've never been under the impression that he doesn't himself truly believe in the ideas he's presenting.Zap Energy was founded in 2017. Lerner had been advocating for DPF fusion funding for years already at that point. LPPFusion has existed since at least 2008, maybe earlier. SFS is so similar, and so much more substantially funded, that i have to conclude that a real fusion success of Zap Energy is actually a vindication of Eric Lerner, despite the fact he's been working with a fraction of the funds and apparently is not part of the Zap Energy project.all that said, i most strongly suspect that the difference in funding is more down to Zap Energy being explicitly an investor grift and thus optimized for that, and LPPFusion being a likely misguided but fully genuine attempt at fusion power first and foremost. Lerner's had over a decade to take the money and run - for better or worse, wrong or right (and unfortunately i do believe his theories are likely wrong here, though i would welcome the opposite outcome), he seems committed to his design for the design's sake, not a pump and dump scheme like nearly every fusion startup appears to be.
>>16250090>meaninglessly pedanticstabilizing external field strength being decreased by self-stabilization of the plasma toroid isn't meaningless or pedantic - it is, in fact, the exact reason spherical tokamak designs exist.>shear-flow stabilization is realwhile "real" and "sufficient for fusion power" are two very, very different things... the rest of the sentence was assuming that the claims were all correct. your eyes evidently hit the word "allegedly" and your brain shut off.
>>16250027You can do it the lazy way where you just use successive overrelaxation with a finite difference scheme. It's actually stupidly easy to do once you have a way to define your geometry. https://mattferraro.dev/posts/poissons-equationOr you can get fancy and write a proper finite element field solver https://www.fieldp.com/femethods.html>>16250067Commonwealth is absolutely full of shit. I'm surprised they haven't gotten sued since they've made knowingly false claims about the timeline for the project and the budget to their investors and the public. I've talked to people from CFS and the head of MIT and there's basically been no work done on a lot of the issues which they'd actually need to produce even the slightest amout of electricity. If they make any money it will be from commercializing the superconducting magnets. Honestly the main reason it exists is they Congress refunded their old fusion experiment in 2016 since it didnt produce any results, so they decided to go for private capital instead.It's not even the first time they've pulled this scam of Tokomak with novel superconducting magnets https://news.mit.edu/2010/fusion-ignition-0510
>>16250027Look up Finite Difference Method if you want it to be "good enough", but also significantly easier to implement.Look up Finite Element Method if you want a better and more robust sim, and don't mind that you're going to hate yourself.
>>16250094>>16250154>>16250158Thanks anons I will look into all the things suggested
>>16250154>Commonwealth is absolutely full of shitThat's disappointing. I guess all these fusion startups are just grifts.
>>16250162Good luck, let us know how it goes.
>>16240450>Power - if you're desperate, I've actually had really good luck adapting the innards of plasma arc lighters to make a cheap and dirty high voltage supplies for classroom demosI can second this - from a casual look at the guts of some of these kinds of lighters, it looks like they all basically just run a little 4V/3.2 mA Li-ion battery into what looks like maybe a timer or some other simple invertor circuit (none of the ICs on the boards have any identifying details and I can't be bothered to dismantle the board and test them) out to a tiny potted transformer - most of the circuitry looks to be running out to the indicator LEDs rather than the actual voltage output. They're all high enough voltage to short any of my meters, but I'm guessing probably a couple thousand volts versus a couple microamps. Enough to get breakdown in air across a gap of maybe a centimeter or two. If you wire them to electrodes in a tube or chamber you can get an okayish glow discharge with argon or helium at lower pressures (only for a few seconds though, at that kind of wimpy current it's not a stable discharge).It's no substitute for a good constant current HV supply or an RF source, but at ~$10-15 a pop they're an extremely good and disposable supply for classroom demos (just be careful with the insulation!).
>>16250097Assume all tech startups are scams until proven otherwise. If Zap or any of these other companies actually deliver some real results, I'll take them seriously. Until then they're just another Solar Roadways.
>>16250104I'd call you a sophist but you're just fallacious, not clever, and not worth the energy.
>>16252012Zap's already reached 3 keV Te
>>16252077What do you want? A cookie? Babby fusors can get to 10-20 keV.
Any hope for someone who just graduated with a Bachelor's in Plasma Engineering to find a job. I was mainly looking into semiconductor stuff (got a few interviews) since a lot of my research was plasma chemistry (specifically graphitic conversion), but I'm honestly getting no dice. I don't want to commit all in to a Master's right now. I don't know if it's just cause the job market is ass, or if I just chose to study something that's not useful.
All this fusion talk is boring, it's just the same old same old. Let's get some more low-T, complex, and astro discussion.Dustychads - how do we feel about Knapek apparently solving the void problem?
>>16245069Just started reading chapter 1. It says the main hurdle for fusion is achieving particle temperatures that can overcome the coulombic force. Is there any way to fold or inject electrons into the beam?Something like D - e - T sounds like it should be able to lower the barrier significantly. Maybe by splicing the nuclear beam with an electron beam?
>>16252938Temperatures actually aren't the real challenge - we can get temperatures that can overcome the Coulomb barrier without *too* much trouble (you can build a simple fusor for several grand and those can easily get hot and dense enough to get *some* fusion happening). The problem is that while fusing is easy, fusing efficiently is not: The electromagnetic confinement of the plasma isn't perfect and usually has lots of leaks and instabilities, using external fields and heating mechanisms costs power, etc. Fusion research is as much engineering as it is physics. The only reason it works so well for the sun is that it's got the gravitational force of a couple quettograms of matter doing the heavy lifting on containment.Adding electrons doesn't really help, because the orbits of the electrons are much bigger than the scales you need to compress the atoms to for the nuclei to fuse, so it doesn't really help much with overcoming repulsion. There's been some and-and-off work over the decades about using muons instead of electrons (they orbit a couple hundred times closer and can significantly reduce the temperatures needed, which would reduce confinement problems, costs of the heating and external fields, etc. significantly, but it has its own problems (the biggest being a. there's no way to efficiently produce muons in large enough quantities that we know of, and b. the muons don't stick around very long, and usually get stuck with the alpha particles generated by the fusion reactions before catalyzing many of them).
>>16252879Interesting paper - I know voids have been a nuisance, especially for micrograv research, so anything that can potentially prevent them from forming in the first place should be very useful. I wonder if the decision to try pulsing the RF source was motivated by the polarity-switching experiments on PK4 (although it looks like the switching here is done pseudorandomly here instead of just periodically).
>>16252842Yeah, the job market is shit across the board, but don't get discouraged, if you're getting interviews you're already doing better than a lot of anons.Semi-conductor stuff is a good area to look at, especially if it's more applicable to your area of study, but don't rule out more generic work. A big part of working in industrial research and engineering is being flexible with working on projects that might be outside your usual wheelhouse, and lots of employers are interested in people who can come in and apply their general experience with research practices or engineering-based problem-solving to come up with solutions for things they're working on. ex. I had a friend who did a BS in aerospace engineering and ended up working for a biotech company designing automated sample testing systems.Try /scg/ if you need more specific advice.
>>16241830>It’s annoying that nobody has managed to put together a decent monograph on the subject yet.In fairness, plasma acceleration is still relatively new. The early theories are only like thirty or forty years old, I think, and it wasn't even demonstrated to be experimentally viable until like five or ten years ago.
>>16233254What actually useful usecases are there for plasma?
>>16233254Thoughts on the plasma magnet?https://www.centauri-dreams.org/2017/12/29/the-plasma-magnet-drive-a-simple-cheap-drive-for-the-solar-system-and-beyond/
>>16257006How do you mean?
>>16257006Most of the practical applications are in plasma processing and plasma chemistry - using plasmas as a means of altering materials, fabricating devices, treating organic materials, producing free radicals to catalyze reactions, etc.
>>16257114Interesting concept, but doesn't seem very practical: Considering typical plasma densities in interplanetary and interstellar space, you'd need the system to be thousands of meters across and generate thousands of amps of current just to get a few measly newtons of thrust.
>>16258280the current isn't really all that difficult. the bigger problem is scale, as you said, plus cooling, since absolutely nobody in their right mind is going to use kilometers of superconducting cable for a dumbass joyride that can't even fucking turn around (also an issue)>>16257114any "go fast and light" method for solar system travel is not thinking long term. the "plasma magnet" is in the unfortunately common position of being too unwieldy for single missions and too inefficient for "solar system space infrastructure" transits. those are most likely going to start as unmanned tugs using transfers between Lagrange point orbits with short burns from conventional engines and long transit times - they'll spend almost no energy OR fuel doing it. those boring ol' chemical propellant reaction thrusters really ARE enough... as long as your whole mindset isn't mired in linear point-to-point transit fantasies.because the concept of space travel that midwits possess is precisely that linear point-to-point fantasy, often their initial ideas become rapidly absurd when they do napkin calculations to determine the needed reaction mass. naturally, because they're midwits, rather than reflect on their assumptions, their kneejerk reaction is "solve the reaction mass problem." always with propulsion types that use little to no reaction mass (this is also why midwits love solar sails so much) but are STUPIDLY weak in terms of both power to thrust (this is why all their designs rapidly approach kilometer-scale solar panels) and acceleration.unironically the actual solution to the "problem" is just taking the black pill that efficient interplanetary transit doesn't happen on convenient timescales (incompatible with their sci-fi worldview, so a nonstarter), plus a better understanding of orbital mechanics, especially low-energy transfers (anything besides simplified Hohmann transfer orbits and gravity assists is beyond their mental capabilities, so also a nonstarter).
>>16257114I don’t think it works. All of Slough’s work neglects the interplanetary magnetic field carried by he solar wind, assuming it doesn’t matter. But it actually ends up putting torque on the spacecraft and completely sending it in a different direction, which makes trajectory planning almost impossible. https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/185206/2/dkogk03813.pdf>>16258280A few newtons of thrust is on the high end compared to most other EP concepts.
>>16259324That’s quitter talk. I’m not sitting around for 14 years waiting on a shipment of Ganymedean spices to complete some ridiculous multi-body assist trajectory, just because nobody wanted to do the hard work of finding an alternative to chemical rockets.Plasma propulsion has actually made great progress in recent years. Ad Astra’s VASIMIR system exceeded 100 kW a few years ago and as of I think 2022 they’ve successfully operated above 80 kW in steady-state for like four days straight.And last I think Howe Industries is supposed to be developing a practical proof-of-concept demonstration of their PPR design.
>>16259952>"quitter talk">followed by "waahhh i don't wanna wait">the rebuttal is fucking VASIMR>only given thrust value is 1.53 Newtons... for 53 FUCKING KILOWATTS. ~0.029 N/kW.>they've been saying "just scale it up bro" for nearly 20 years while struggling to cool their small scale demonstrators>"great progress in recent years"except VASIMR was over 50kW in fucking 2008 (PDF related) - we've ALREADY been sitting and waiting for 11 years for them to move up a whole 50kW more.0.029 N/kW from 2019 is about 15% worse than the 2009 NEXT gridded ion thruster used on DART (~0.034 N/kW), and the NEXT thruster has both stress tests on the order of multiple YEARS of continuous running (rather than tens of hours with VASIMR) and a heat output that's feasible to cool.i'd actually like to thank you for replying with this, because VASIMR is a poster child of what i'm talking about - it's the engine that impatient midwits were cheering for the asinine "Mars in 39 days" claim over a decade ago. the claim that required 200MW fed to a thruster by a power plant with orders of magnitude larger power-to-weight ratio than anything ever sent to space, and required ignoring the fact the thruster would only be ~60% efficient WITH room temperature superconductors, dumping 80 fucking megawatts of heat into the spacecraft.midwits are the ones who regurgitate the corporate marketing claims and think saying "Ad Astra's going to do X" or "Howe Industries is going to do Y" is equivalent to providing support for their delusions, rather than merely revealing who's currently selling them the delusion.midwits are also the ones who think it's "VASIMIR" and not "VASIMR"
>>16233256Piel's pretty good, but I also feel like he falls into the same category as Jackon, where you're going to spend a lot of time and effort filling in the gaps of the derivations that he's omitted because 'it is trivially obvious to even the most casual of observers' yadda yadda. For a reference text I think it's great, but if you're trying to learn general plasma physics, Chen or Gurnett are better starting points.
>>16257006its bright hot and shiny
>>16258280>you'd need the system to be thousands of meters across and generate thousands of amps of current just to get a few measly newtons of thrust.No, not at all, the tech demonstrator concept consists of just a superconducting coil a couple of meters in diameter see-https://www.researchgate.net/publication/358839818_Jupiter_Observing_Velocity_Experiment_JOVE_Introduction_to_Wind_Rider_Solar_Electric_Propulsion_Demonstrator_and_Science_Objectives
>>16259324>any "go fast and light" method for solar system travel is not thinking long term. the "plasma magnet" is in the unfortunately common position of being too unwieldy for single missions and too inefficient for "solar system space infrastructure" transitsI don't care, so send out a swarm of them, if this is really as fast as it is claimed to be then that would be totally worth doing for rapid fast flyby missions where right now they cost billions of dollars and take half a decade+ cruise time + gravity assist time just to fly past a planet at the end, that's whats actually inefficient and wasteful.Anyways the speed you can get with a plasma magnet (basically speed of the solar wind 300-500km/s) makes it worth it no matter what imo>>16259646>But it actually ends up putting torque on the spacecraft and completely sending it in a different direction, which makes trajectory planning almost impossible. Damn I didn't know about that, it does seem like it would inherently be hard to control, like a parachute in the wind but again sending out a swarm of them is one solution, other more finer control solutions may be devised too, doesn't seem like a dealbreaker for fast, cheap and rapid planetary flybys
>>16257006This is a bit like asking 'what actually useful usecases are there for solids?'
>>16260115Technically you could do a funny and beam the power to solve the energy density problem. Also using some novel radiators like liquid droplets. But it'd be a fucking major engineering challenge, its like an Atlas to Starship leap in technology from currently available spacecraft with electric propulsion.
>>16261704>what actually useful usecases are there for solids?'Well? Name three
>>16259324Dogshit blackpill. If I need a 4d grid tracer and a background in linear dynamics to find your trajectory you should kill yourself. I agree that brachistochrones are unattainable without massive breakthroughs in fusion or something, but I define a convenient timeline as around 1-3 months to Mars and 6-12 months to Jupiter. You can attain that shit absolutely fine enough with a souped up electric drive and the infrastructure of beamed power stations. Radiators are solvable, everything is fucking solvable. We use diesel generators instead of sails to get somewhere faster even if it takes more energy and resources to do it.
>>16262046>Atlas to Starship leap in technologyno. not even fucking close. more like a "diesel engine to nuclear powered ship" in terms of fundamentally different architecture at the most basic level with completely different design constraints for the entire craft.power beaming is another midwit favorite because it absolves them of thinking about power production completely - it's off the space ship, and thus out of their little heads. do they have solutions for the fundamental issues of optical dispersion and the additional inefficiencies of conversion to usable power (which is yet MORE heat)? or perhaps even the economics of producing the beamed power just to beam it to move a crate faster when you could just fucking wait a few more months? no. nothing even approaching it.the fact you're using "Atlas to Starship" as a technology "leap" yardstick is also... very midwit.and so is your offhand dismissal of the cooling problem with the peak midwit "novel radiators like liquid droplet" statement. you're regurgitating a buzzword concept you saw once in some popsci tabloid or youtube video because you think it will solve all your problems with literal magic being presented under the marketing name "future innovation."your conception of the science is a marketing gimmick. i'm sorry you had to find out this way.>>16262068>the math is TOO HAAAARDDDD>i'm going to try to mask that by using a big word>everything is solvablethe physical, geometric laws constraining these systems are not "solvable" without breaking them. there really ARE physically impossible combinations of transit and craft configurations, regardless of whatever nebulous fantasy future innovations you must invoke to preserve your escapism.what is it about electromagnetic spacecraft propulsion that compels midwits to out themselves like this?
>>16262181You're completely fucking retarded if you think high delta-v drives would be used for shipping crates. The immediately obvious reason to use them for anyone with a brain is crewed vehicles. The main reason droplet radiators aren't used is that there's no use for them yet. Its silicone oil being shot out of a showerhead and then recycled into a heat exchanger and you call it magic because you're the midwit.
>>16262830>crewed vehicleswill be few and far between. certainly not worth massive power beaming systems just for transit. this isn't going to look like your sci-fi with constant crewed travel between locations, i'm sorry. reality isn't Terra Invicta.>The main reason droplet radiators aren't used is that there's no use for them yetno, they're actually completely untested in non-laboratory vacuum where they have to deal with the acceleration of the craft and incident light/particles. there's no way to prevent droplet loss to acceleration; the reported tolerance to changes in craft momentum is roughly 0.01 m/s^2 WITH magnetic focusing, which seriously limits your ability to perform orbital transfer maneuvers of ANY kind. a 1km/s delta-V change will now require an engine burn longer than an entire Earth day just to avoid spraying all your coolant out of the spacecraft. even angled edgewise to the sun, you'll still need to deal with incident heating of your pump apparatus and the droplets - none of the tests have accounted for this.faster transfers than the months-to-years-long normal Hohmann transfer orbits require substantially greater delta-V. Mars in 1-3 months is absolutely retarded. Jupiter in 6-12 months is absolutely retarded. the craft would be moving several times faster than FLYBY speeds (those don't take as long because you're not transferring to an orbit around the object; you can't use those transit speeds as a yardstick for interplanetary travel), and require massive changes in acceleration to match.as much as i've been clowning on electromagnetic systems in space, your better bet for better cooling is something like dusty plasma or, more realistically, just larger bog-standard radiator plates with nanostructured surfaces that exceed Stefan-Boltzmann emissivity of 1 (i'm dubious of how credible reports of this are, but i have seen it in the literature).
>>16259324I play kerbal space program, you can certainly increase travel times if you have more delta V while still working with sane orbital mechanics
>>16263654Well, if your just bitching that a lot of the high ISP drives are too low thrust for all that velocity to be applied within <shortened travel period> then yeah I agree
>>16263657I agree with you entirely I have no idea why I tried to argue this
>>16262046How about just using an actual good engine like one of the various nuclear propulsion concepts?
>>16262830high delta V is kind of useless if the thrust is so low that travel times are so long, what you actually meant to say was that ion engines are more useful for uncrewed vehicles were saving on reaction mass is more valueble than mission time. For a crewed vehicle piling fuel tanks on a faster engine (chemical or nuclear thermal realistically) is basically necessary.
The last good thread on /sci/
What the fuck is the deal with ambipolar diffusion? I've seen it come up in a few topics I've read up on and I think I *sort* of get the general concept (stuff spreads out in the plasma and I guess it makes fields). But I'm only starting my third year of undergrad and I can't make heads or tails of some of the math. Is this the sort of thing that'll make more sense if I surviev E&M?
>>16265148Conceptually, that's the gist, but yeah, in terms of the math and physical modelling it's kind of a bitch.So basically, if you look at the Navier-Stokes equation for a charged species in a weakly-ionized, low-temperature plasma, you've basically got four parts:[math]-k_B T_s \nabla n_s + q_s n_s \overline{E} - m_s n_s \nu_{sn} \overline{v}_s = m_s n_s \left( \frac{\partial \; \overline{v}_s}{\partial t}+\left( \overline{v}_s \cdot \nabla \right) \overline{v}_s \right)[/math]The first part is your pressure gradient (we'll assume an ideal gas with constant temperature and substitute for [math]\nabla P[/math]), the second part is your electric force density, the third part is your force density from collisions with neutrals, and the right-hand side is your mass density multiplied by your local and convective accelerations (how is velocity changing within each volume element, and how is velocity changing globally - remember that N-S is basically just Newton's 2nd Law on a per volume basis).Now, if you assume that your fluid reaches a steady-state and the convective derivative is small, you can take the right-hand side to be zero. If you define a mobility coefficient, [math]\mu_s = q_s / m_s \nu_{sn}[/math] , a diffusion coefficient, [math]D_s = k_B T_s / m_s \nu_{sn}[/math] , and a flux, [math]\overline{\Gamma}_s = n_s \overline{v}_s[/math] , then you can redefine N-S in terms of a flux equation:[math]\overline{\Gamma}_s = \mu_s n_s \overline{E} - D_s \nabla n_s[/math]The flux of charged particles in or out of a volume is the difference between the mobility of the charges (the balance between the electric force pushing them along and collisions with neutrals resisting that push) and their diffusion (the tendency for collisions within a species to cause things to diffuse outward).
(continued)If the plasma is quasineutral ([math]n_e \sim n_i = n[/math]), it's reasonable to assume that the fluxes of electrons and ions will be the same ([math]\overline{\Gamma}_e \sim \overline{\Gamma}_i = \overline{\Gamma}[/math]), and if you set the two fluxes equal, you can work out that the fluxes equal each other at a particular electric field:[math]\overline{E} = \overline{E}_a = -\left(\frac{D_e - D_i}{\mu_e + \mu_i}\right) \frac{\nabla n}{n}[/math]This is the ambipolar electric field. And if you substitute this back into the flux equation, you get the common flux of the plasma:[math]\Gamma = -\left(\frac{\mu_e D_i + \mu_i D_e}{\mu_e + \mu_i} \right)\nabla n = - D_a \nabla n[/math]Where [math]D_a[/math] is the ambipolar diffusion coefficient. If you take the same flux definition and apply it to your continuity equation (conservation of mass):[math]\frac{\partial n}{\partial t} + \nabla \cdot \overline{\Gamma} = 0[/math]And putting in your coefficient, your continuity equation turns into a nice little diffusion equation:[math]\frac{\partial n}{\partial t} = D_a{\nabla}^2 n[/math]Diffusion is a pretty important concept if you do any kind of research into transport phenomena (it also gets *way* messier if you throw in magnetic fields, but let's be honest, what *doesn't* get messier if you throw in magnetic fields?). The ambipolar electric field is also pretty important in anything involving low-temperature or dusty plasmas (since it usually adds to whatever background electric field you have in the plasma). Thankfully, in LTPs you can pretty safely take [math]\mu_e \gg \mu_i[/math] and [math]D_e \gg D_i[/math], which reduces the ambipolar field to:[math]\overline{E}_a = -\frac{k_B T_e}{e}\frac{\nabla n}{n}[/math]Which is pretty fucking nice.Also apologies for any signs or subscripts I might have fucked up in the above - I'm copying this out of my old grad notes which are, admittedly, pretty shit.
>>16265335>>16265338nice effortposting
>>16265335Why would plasma follow ideal gas laws?
>>16266387It actually follows from general thermodynamic considerations from the assumption that the potential energy is much smaller than the thermal energy [math] \Gamma \ll 1 [/math] and the fact that this means particle positions are uncorrelated [math] g(\overrightarrow{r}) =1 [/math]In the canonical ensemble, you have [eqn] P=\left( \frac{\partial F}{\partial V}\right)_{T,N} [/eqn]where [math] F [/math] is the Helmholtz free energy related to the canonical partition function by [eqn] F = -k_B T \ln(Q_N) [/eqn] and the partition function is [eqn] \frac{1}{N! \lambda_{th}^{3N}} \int \exp(-\Phi_N/k_B T) d\overrightarrow{r}^N [/eqn] in which the integral is carried out over all N particles and the potential [eqn] \Phi_N = \sum_{i=1}^N q_i\phi(\overrightarrow{r}_i)[/eqn]The fact that particles are uncorrelated means the potential [math] \Phi_N \rightarrow 0 [/math] so the argument of the integral is [math] \exp(0)=1 [/math] and the integral just turns into [math] V^N [/math] So after substituting the ideal gas partition function into the pressure relation, you get [eqn] P = k_B T \frac{1}{Q_N} \frac{\partial Q_N}{\partial V} = k_B T \frac{\frac{\partial V^N}{\partial V}}{V^N} = k_B T \frac{N}{V} = nk_B T [/eqn] the ideal gas law
>>16266387To follow up on what >>16266554 said - not all plasma species *do* follow an ideal gas law, and even those that do don't always follow it for all plasma conditions, but it's a pretty reliable approximation that (so far as I know) really only breaks down at very very high temperatures and/or densities like when you start getting into things like neutron star matter where electron degeneracy comes into play or strongly coupled plasmas where the potential energy becomes comparable to the thermal energy, or dusty plasmas where your coupling parameter becomes variable with the dust charge, etc.
>>16266601Sorry, I meant white dwarf stars, not neutron stars, although I guess it applies there as well.
>>16266603WD yesNS noRemember - a White Dwarf star is fully ionized (albeit degenerate) matter whereas a Neutron Star is neutral because the protons and electrons have combined to form neutral neutrons.
>>16266656The core has collapsed to form neutrons, but the less dense outer crust consists of pressure ionized iron which is strongly coupled enough to form a Coulomb solid.
>>16266742the fuck is a coulomb solid?
>>16267226At around [math] \Gamma=180 [/math] the ion component of the plasma undergoes a freezing transition into into a classical analogue of a Wigner crystal. There’s a decent amount about them in Ichimaru’s Statistical Plasma Physics volume 2 Condensed Plasmas.
>>16266742>>16267434Also pressure ionization is where the matter is dense enough that electrons in the same orbital from neighboring atoms are close enough that Pauli exclusion principle forces push the Fermi energy above that of the highest possible bound state. This frees the outer electrons and allows the iron to fully ionized despite the fact that it’s too cold for full thermal ionization as predicted by the Saha equation.
How is /ppg/ taking the news about ITER?QRD for those who haven't heard: Team management has pushed the timeline for completion of the project by a decade - first plasma delayed to 2034, D-T burning delayed to 2039 at the earliest, and a minimum of $5.5B USD added to the projected costs of finishing construction.https://physicsworld.com/a/iter-fusion-reactor-hit-by-massive-decade-long-delay-and-e5bn-price-hike/I expect the ITER town hall at DPP this October is gonna be fucking *rough*. I don't envy whoever's going to be representing this year.
>>16267675It's hardly news for anyone who's been watching closely. ITER employees have been privately saying 2034 or 2035 for a while now.The article says French regulators halted construction "briefly" but it was actually almost 3 years. The reason the blocked it was because they had different segments of the vacuum vessel all made in different countries, and the Korean and Italian ones were damaged during manufacturing and wouldn't fit together, but they sent them to ITER anyway.https://pubs.aip.org/physicstoday/article/75/5/20/2848487/Further-delays-at-ITER-are-certain-but-their outlines some other issues including one of their plasma engineers killing himself over management pressure.There have also been a lot of high profile resignations from the project in the past few years.
>>16267675do we have ANY specific detalis as to why? this is literally the second time in the last two decades that first plasma has been delayed to "nine years from now" (happened in 2016, too, though that time at least the first plasma plan was 4 years out in 2020 as opposed to only a year away.)this is a fucking disaster for tokamaks, and will likely hurt all fusion projects to some degree.a decade long delay with construction of the magnets finally complete after all these years is... extremely concerning.it's the kind of thing you only do if you... don't actually think ITER is going to work at all.
>>16267675I used to be down the hall from a guy who collaborated quite frequently with ITER and he was always very negative about the whole thing. His opinion over private conversations seemed to be that there was a lot of money that just got sucked up into a project that could've been great but was being ruined by mismanagement and countries squabbling over petty things. He also mentioned quality was suffering due to people being severely overworked, although I don't know specifics, but >>16267713>one of their plasma engineers killing himself over management pressuremade me recall that snippet of conversation.He seemed to think ITER was actually getting in the way of fusion making faster progress via smaller projects, which to me initially sounded insane, but it seems that he had a point.>>16267733>it's the kind of thing you only do if you... don't actually think ITER is going to work at all.Well... some people don't.
>>16267733What the biggest issue is depends on who you ask, but in reality it's not just one thing: There's been a number of major engineering, worker, and management issues during the project's history - a lot of the components are seeing worse-than-expected performances, several strikes have seriously hindered production (to say nothing of Coivd), and there've been complaints about mismanagement of the project since, basically, day one.While the motivation for making this such a big international collaboration is understandable, the way in which it's been handled has been a complete clusterfuck of international bureaucracy - many of the engineering and production tasks distributed between different countries gave little regard for their actual capabilities or for ensuring consistency across the project. As >>16267713 points out they halted work for almost three years having to sort out damage and inconsistencies between sections of the vacuum chamber made in different countries. There's also been a lot of indications or outright confirmations over the last 10-15 years of the supervisory council ignoring recommendations or concerns from different teams, which has led to a number of resignations from team leaders, several costly mistakes that the board refused to acknowledge until they were basically forced to disclose internal communications, and is implicated in at least one high profile suicide.And this is to say nothing of the pressure that everyone working on the project is under: A lot of researchers in fusion feel like the community has bet the proverbial farm on ITER, so there's a lot pressure to deliver. This, as well as the vocal and often vitriolic disapproval that these researchers get from those who disapprove of the ITER project and its setbacks just adds more stress to people who are already dealing with too much, and increases the chance of further mistakes and burnout.
>>16267770The way I understand the history, ITER is almost literally a singular conglomerate project born from the merging of national projects from the tokamak stampede (after JET did so for European projects, ironically), and has itself even crushed other tokamak projects (it is arguably most responsible for killing JET last year, which is still the best tokamak we had).About the only fusion projects that the stampede didn't cripple were ICF, because they were and are nearly untouchable: ICF is the only process we have to experimentally simulate the conditions of thermonuclear weapons in the context of the test bans. It's why NIF was built, and it's why the Z Machine was built (uses Z-pinch to accelerate the plasma but IIRC fusion confinement is still inertial via a ring of converging accelerator beams). Only thermonuclear powers have such facilities, but every thermonuclear power does (though AFAIK nobody has equivalents to NIF or the Z Machine). Hell, the only reason the Z Machine uses Z-pinches is because lasers weren't good enough for ICF at the time. As soon as they were? The Shiva laser is built, then Nova, then NIF (still with quite inefficient lasers by today's standards, BTW), and the Z Machine pivots to testing things with its ludicrously powerful radiation generating ability. Nuclear weapons are a different fucking ballgame to everything else - and so far it's the only ballgame where fusion has met with much success.It certainly isn't unreasonable for someone to see ITER as a net negative to fusion. Its greatest legacy so far has been dampening both interest and investment across the board every few years with new delays and cost overruns, all while consuming an enormous proportion of all fusion investment that isn't directly sustained by MIC requirements (and just happens to spit out test results useful to fusion energy), and being, SOMEHOW, less open with its information than fucking classified nuclear weapons research facilities seem to be.
This entire thread is one big schizophrenic samefag session
>>16267999are you lost, anon?
>>16268199Likely the guy crossposting between here and /sfg/ about ITER
>>16267953ITER is like if Joe Biden was a nuclear reactor
>>16267953>Its greatest legacy so far has been dampening both interest and investment across the board every few years with new delays and cost overruns, all while consuming an enormous proportion of all fusion investment that isn't directly sustained by MIC requirements (and just happens to spit out test results useful to fusion energy)I came to agree with this over time. Initially I wondered how we could possibly do better by going smaller with such an ambitious program but now I've come to agree with the guy who first suggested it to me that international squabbling is ruining any chance of ITER doing anything good. I don't know whether those startups will achieve anything, but it's certainly worth giving it a shot if ITER is going to continue behaving like this.
What do you guys think are the most interesting problems in the field right now, and what makes them interesting? Ideally, I'd like to get a range of opinions in three categories:>theoretical>computational>engineering
>>16268975It depends entirely on who you ask and what subfield they're in.Ask someone in space plasmas and they'll say it's understanding plasma turbulence and magnetic reconnectionAsk someone in dusty plasmas and they'll probably bring up dust charging behavior or high B-field phenomenaAsk someone in magnetic confinement fusion and they'll probably say it's magnetic islands and predicting disruptive instabilities Ask someone in plasma instrumentation and they'll tell you it's the development of non-disruptive diagnostics.Etc. etc. etc.Plasma physics is a ridiculously active field, all things considered.
>>16269255Yes, which is why I wanted a range of opinions. It's not a contest to get a correct answer, I just like hearing about what people are interested in and what's active in their fields, and why it's an interesting problem. It's just a discussion stimulator.
>>16268963I don't buy... really any of the startups' claims so far. They aren't as constrained to be truthful about their projects as even universities are, and there is, especially with this recent rush of VC funding and interest, a massive incentive for dishonesty through unfounded speculation presented as "proven science" in order to gain investment. If I've learned anything from the history of tech investment, it's that investors are fucking retarded and staggeringly easy to dupe.I expect most commercialization plans will be walked back as they approach, again and again (several companies have already done this by just... quietly pushing their projections a few years further), and some of these companies will hit barriers that simply cannot be overcome by their fusion designs at any feasible scale. I very much believe we're going to see mostly repeats of CTFusion: scale mockups that never worked in the first place and abysmal data sharing, with literally no viable path to scientific breakeven, let alone engineering breakeven.For fuck's sake, even the behemoth that is CFS is relying on a tritium fuel cycle that simply doesn't exist yet outside of theory. Betting your whole system on the tritium fuel cycle is essentially like banking on the idea that U-238 -> U-235 breeder reactors work before you've even built an enriched uranium reactor. And the next biggest (IIRC), Helion, is banking on a two-stage helium-3 breeder cycle with tritium breeding as the first step.
>>16269279I don't see this going well with these startups either, but without this being too specific, I was once in a certain institute which scrapped some stuff we were developing for a fusion project and China was the very, very enthusiastic buyer. What I think is going to happen instead is that a non-ITER player will eventually emerge, and it's quite likely to be China, in my opinion. They're pursuing this much more aggressively than any western country I know of, and they spent an enormous amount of cash on something our government/higher-ups viewed as scrap (despite objections from people who knew better - but of course, money has a way of going into the pockets of the right people on big deals like this, and there's little you can do).I think the startups probably are going to hit that brick wall as you say, but I think a Chinese-government backed initiative may make real progress. If that happens, I expect the US at least may go into panic mode and start throwing cash at some kind of US initiative. I don't think any European is capable of effectively running a national fusion project at this point. They seem intent on turning themselves into museums instead. Anyway, that's what I'd cautiously bet on happening with fusion in the future, some time over the next decade.
>>16268975i'm a simple man: for me, it's the dynamics of the solar magnetic field.lots of interesting models and implications for internal stellar structure.
>>16269277Well, anything there that you'd like to know more about?
>>16269279>>16269290You've got to take all these startup projects with a grain of salt; my rule of thumb is not to take anyone seriously until after they make their data available (it's the same reason I'm reluctant to give much credibility to most of China's claims).At a bare minimum, though, I commend the private sector for being pretty much the only parties in the game that are actually going back and revisiting earlier confinement schemes with fresh eyes. Everyone was so quick to go all-in on tokamaks that we left a whole lot of ideas by the wayside: Magnetic mirrors, z-pinches, torsatrons, etc.Sure, it's still more than a little likely that none of them will be good enough for sustainable burning, but just the fact that *anyone* is actually saying "hey, let's apply everything we've learned the last ~50 years and see just how much we can improve this stuff" is a positive development impo.
>>16268975Charging dynamics in complex plasmas.1) It's easily the most fundamental physical parameter in complex plasma systems, and yet despite almost a century of studying the behavior of dust in a plasma, we still struggle to accurately predict charging behavior or develop a universal model for it. We have some partial models, sure - OML, discrete charging, Draine-Sutin, Natonson, etc.; some of them can even accurately predict behavior to within an order of magnitude, but what works for modelling charging in an interstellar plasma doesn't work for a processing plasma or a fusion plasma, what works for a non-magnetized plasma doesn't work for a magnetized plasma, what works for a fully ionized plasma doesn't work for a weakly ionized plasma and so on. Every new physical interaction or mechanism you change or introduce completely and utterly alters the charging behavior, which subsequently changes all of the other dynamics of the system.2) It's a simultaneous theoretical, computational, and experimental problem, which is fun because you get each camp pushing their own ideas while having to also try and work within the constraints of the results that the other two camps are getting.
>>16269298>>16270487any favourite reads?
>>16233254ok plasma bros, i have a very weird questionHow hard is it to make a PURE ELECTRON or PURE ION 'plasma', consisting entirely of one of these particle species?
>>16271236It’s very easy for electrons, since there are so many ways to produce free electrons from solids like thermionic/secondary electron/field emission. Ions are a bit harder and usually involve pulling them electrostatically from an existing neutral plasma while using a biased control grid to prevent electrons from being pulled along. There’s a lot more details in chapter 7 of Humphries book http://www.fieldp.com/documents/ChargedParticleBeams.pdfConfining non-neutral plasmas is actually much easier than in the neutral case, since collisions between identical particles do not cause the plasma to diffuse to the walls, and space charge repulsion can be counteracted by an applied axial magnetic field which caused the plasma to effectively behave as a rigid rotor. So things like electrostatic Penning or RF Paul traps can be used to confine them for hours or days. Also since single species plasmas won’t recombine, you can cool them to cryogenic temperatures where they exhibit liquid or solid-like behaviors.
>>16271338Thank you anon, i have a personal idea for a fusion neutron source that i am trying to work out. The concept is basically to generate a pure deuterium ion target cloud inside of something like a penning trap, and then to shoot a beam of pure deuterons into it. Somewhat like traditional IEC but far cleaner.The mathematics are questionable and require serious analysis, the construction of such a device is very questionable at larger scales but there are reasons to think it could be a highly interesting arrangement.I wish i had your plasma physics knowledge, as a mere mechanical engineer whose been bitten by the bug of particle physics i feel so lost trying to determine things like exactly how hard it is to reliably ionize elements via magnets / lasers, or otherwise how long such bodies of particles could be reliably kept separate..
>>16271338if i charged you with the task of making a high z pure ion plasma, how would you go about it?I dont want to abuse your time by asking such a hard question but you seem really smart and i have a very cool idea!
>>16271351>as a mere mechanical engineer whose been bitten by the bug of particle physics i feel so lost trying to determine things like exactly how hard it is to reliably ionize elements via magnetsThe good news is you don't need a knowledge of particle physics to understand plasmas. What you need is nearly the same as what you've already got. Just brush up on your electrodynamics and that's the bulk of the foundations already done. The obstacles in front of you are greater in your mind than in reality.
>>16271408To get high charge state ions, you need to make a plasma with very high electron density since electron impact ionization cross sections rapidly decrease with charge state, and the ions will charge exchange with neutral gas.Easiest way would to use a high power CO2 laser with small spot size incident on a thin target of the material you want. This ablates a plasma on the other side of the target which can easily have ions with charge states of around 20-30 which can be extracted downstream. You can get fancier with electron beam ion source traps for higher ionization.https://www.slac.stanford.edu/econf/C210711/papers/2205.12873.pdf is a good overview of ion source options.>>16271351You gain nothing from having the target be pure deuterium ions. You can have much higher deuterium densities with a solid target impregnated with deuterium. This is what most commercial DD and DT neutron sources do.https://www.thermofisher.com/search/browse/featured/us/en/80012997/https://www.starfireindustries.com/ngen.htmlThere's no good way to get high efficiencies out of beam target fusion because the beam scattering cross section is so much larger than the fusion cross section.
>>16271482Thank you plasmabro. That was an excellent answer that you gave me.For your gratification, it is worth mentioning that the vast majority of beam target fuel ion thermalization comes from electron-ion collisions (afaik), so for a given beam power you would get MANY fold more fusion events, as more high impact ion ion collisions would occur.Bremsstrahlung in a thermonuclear system is also primarily an electron phenomenon.
>>16271482This is the last question i wanted to ask, i feel almost guilty learning this much from you!If you would humor me anon, if you had a carte blanche budget to make a pulsed power machine capable of creating a small dense pure ion plasma, do you have any ideas of how you would make such a device?if im asking too much you dont have to respond, thanks for all the information
>>16271582Probably something similar to the bipolar double pulse TEMP series of high current ion diodes from Tomsk.It uses a Marx to charge the outer and middle conductor of a triaxial Blumlein with a negative pulse, which forms a plasma from an explosive emission cathode. The negative pulse is used to charge the inner and center conductors of the Blumlein through the diode, which is then triggered to form a positive voltage pulse which pulls the ions from the emitted plasma while magnetically self-insulating the electrons. The insulated electron flow also allows the ion current to exceed the space-charge limit.
man this thread is comfywhat a breath of fresh air on this board
>>16271697Thats awesome, thank you for sharing that paper.I wonder what charge states an explosively pumped flux generator could produce
brainlet here: how does a double layer work? shouldn't it just recombine immediately? the ions and electrons are right next to each other. is it like some sort of "three stooges in a doorway" situation where the density of each charged layer is such that getting close enough to the other layer to recombine is hindered by electrostatic repulsion tangent to the layer? it seems to me like anything like that would be both extraordinarily unstable and behave differently for electrons vs ions. but i'm also a brainlet.the wikipedia page isn't all that helpful (as far as i can tell), and there appears to be a long history of somebody (probably Duncan Bryant, according to the talk page and the fact a lot of the edits cite Duncan Bryant) editing it to claim double layers can't accelerate particles. i don't even know enough about double layers to know whether that's a schizo claim or Bryant is just correct.
>>16233254reminder to all fusion bros that we are all gonna make it
>>16273766there's a small part of me that wonders if nearly every fusion design, no matter how off-the-wall, has a viable path to power generation, but we've just never built any of them big enough.
>>16273218I don't know (I haven't encountered double layers anywhere in my own research), but I would venture a guess that maybe the recombination rate is being limited by the separation between ion and electron layers. Maybe you're only getting a significant amount of recombination near the interface. If the plasma is being replenished then that would allow the structure to be stable(ish).I dunno, it's a good question, I wish I knew more about double layers.Also, fucking hell, that talk section could be right out of a shitposting thread.
>>16273218I also don’t know much about double layers, but from the phase space and density plots in these papers https://www.degruyter.com/document/doi/10.1515/zna-1983-1102/pdfhttps://www.academia.edu/download/69502443/0370-1573_2886_2990043-820210912-29244-1yxn3lj.pdfIt looks like the trapped ions and electrons are actually stuck in the regions of opposite charge, and that instead of recombining the particles are just accelerated past the double layer entirely. This is consistent with the fact that double layers usually need to be much smaller than the mean free path to form, since the charge imbalance is mostly due to the particles free streaming past each other,I’m pretty sure there also needs to be some external source of voltage to prevent the layer from collapsing.Bryant is probably wrong since particles in the aurora aren’t starting infinitely far away from the double layer and the surrounding charge density isn’t stationary for all time.
>>16275320Nice find
>>16269279>Helion, is banking on a two-stage helium-3 breeder cycle with tritium breeding as the first step.I thought they were using deuterium and He-3 and avoiding tritium
>>16276952Helium-3 is in a very similar (except worse) supply situation to tritium - there's legitimately not enough of it on this planet to run a fusion reactor.The only way to obtain more of it is either gambling on space mining delusions, or breeding more Helium-3: Tritium decays into Helium-3, and the decay of tritium is currently the only viable source of Helium-3. You have to breed tritium.D-D fusion produces tritium about 50% of the time. Neutron irradiating lithium also creates one atom of tritium. That's tritium breeding. However, the temperatures of D-D fusion are more than sufficient for the D-T reaction, which consumes tritium, requiring an excess of tritium production - the lithium is non-negotiable. Extracting excess tritium... somehow... is how such a reactor is meant to work. Neither the lithium blanket nor the selective extraction of tritium have been tested in a fusion reactor at scale.You might ask, "What about that D-D Helium-3, the other 50% of the time?" Unfortunately, Helium-3 has a rather large neutron cross-section, so large in fact that some suggest injecting Helium-3 specifically to absorb fusion neutrons to reduce neutron flux. The very process that's creating it is both destroying it and consuming neutrons, meaning you have to do more D-D and D-T fusion to maintain the necessary neutron flux to actually do tritium breeding (which in turn makes more Helium-3) - you basically need to overwhelm the Helium-3 just for your breeder cycle to function. Again, the lithium is non-negotiable.Bottom line, the only way they can get Helium-3 is by obtaining or co-producing tritium. Fission reactors make tritium just by sitting in deuterated water (can't do this with fusion because the reactor needs that extra tritium continuously, hence the blanket), but "fission bad, fusion good," so that's off the table.Also, all that lithium is gone forever. Rare and useful lithium, not abundant and unused deuterium, is the actual fuel in practice.
>>16277498I'd assumed they'd got a source somehow. Otherwise their entire project seems incredibly deceptive. They're portraying themselves as though they've got a plausible idea for a reactor but there seems to be absolutely no substance whatsoever, yet they're pulling in potentially a 9 figure investment.
>>16277501The company has always been incredibly deceptive.
>>16277498Yeah, it's concerning how much the fusion community either completely ignores the issues with lack of abundance for a lot of their fuels/catalysts/etc. or just writes it off as "oh, we'll deal with that once we have fusion working."I remember reading an article talking about ITER, where they casually dropped that a practical ITER/DEMO-type reactor would need to consume, I think, something like a quarter-ton of a tritium a year to maintain operations. As I recall, that's about as much tritium in one year as the US nuclear weapons program produced over about 50 years!It's the same with folks looking at muon catalyzed fusion. Sure, it works, but we don't have the technology to efficiently generate muons in *remotely* a high enough concentration to make μCF practical. Which makes the papers wanking about ideal configurations and parameters for catalyzing reactions seem moot, and all the claims by companies investigating it seem scammy.
>>16277498>>16278496Yeah, I didn't even mention that we're meaningfully further away from D-D fusion than we are from D-T fusion - it seems like a small difference in necessary fusion conditions, but it legitimately requires different fusion reactor parameters than D-T fusion does. Nearly all tokamaks I'm aware of, including the plan for DEMO reactors, are going for D-T fusion.
Did you know that plasma can actually result in black flames?https://www.youtube.com/watch?v=EhePz0Jlz_k
>>16278496Yeah, after ITER is done with experiments, there will be less than 5kg of tritium left in the civilian inventory with effectively no way to make more since nearly every candu reactor will be close to decommissioning.I know the UKAEA is finally starting up some projects foe tritium breeding and extraction from a blanket, but I don't see a clear path to it ever being sustainable. There's just no way to have enough coverage of the walls by the blanket with all of the feedthroughs for diagnostics,fuel injection and heating to actually capture enough of the fusion neutrons.Even in the most optimistic scenarios, it'd only possible to cover the burned fuel + radioactive decay ,which means there needs to be a way to recover close to 100% of the unspent tritium. This doesn't seem possible even if it's somehow possible to filter out of the vacuum system since so much of it will adsorb and diffuse into the walls
>>16280126>after ITER is done with experiments, there will be less than 5kg of tritium left in the civilian inventory with effectively no way to make moreFucking hell, did no one bother to think this shit through??
>>16280396no, because that's an "eNgInEeRiNg pRoBlEm," and certain physicists (especially the ones who like to be in charge of things more than they like doing science) have a habit of considering themselves above having to solve such problems, and thus very frequently find themselves utterly stymied by the 'simple' engineering problems that they'd neglected. just because a problem is 'simple' to calculate mathematically doesn't mean it won't fuck your shit up if you failed to account for it in your design phase.muon catalyzed fusion is probably the epitome of this for fusion - it's one of the dumbest ideas in the history of fusion research. muons aren't even truly a catalyst, since they consume themselves simply by existing wuth a half-life of 2.2 microseconds, requiring constant production at scales beyond anything ever achieved by orders of magnitude, and a muon production system that doesn't take more energy than the muons could possibly produce via fusion. no such production system exists, and there aren't even theoretical designs for one.
>>16279085>>16278496>>16280126>>16281122Isn't it generally assumed that practical fusion reactors would have a neutron multiplier-lithium 6 breeding blanket?
>>16280126oh
>>16281122This is a fairly overwrought take. These ideas are fine. There's no problem with people working on MCF. All ideas come before they can be executed in practice. It would be nice if we had a way to solve it, but a physicist is typically not capable of doing it because it isn't their job. They don't have that background. That's why they say it's an engineering problem. This is like computer scientists being mad that other scientists write such comparatively bad code.
>>16281935ITER will only have a burn fraction of 0.36%, so the remaining 99.64% of unturned fuel will somehow need to be recovered, separated from other elements of the gas stream and reinjected. This technology doesn’t exist yet, and will likely not even be ready when ITER starts up. Also downtime for maintenance will be enough that the blanket will not be able to make up even for the burned fuel. Since tritium diffuses through materials so easily, some of it will end up in the coolant stream too, which will need to be decontaminated. Scaling up the detritiation procedure from CANDU reactors is unworkable with the flow rates you need and would end up using a significant fraction of the total power needed to run the reactor.Nobody’s even built a blanket yet so there’s no experimental data on its performance and there are uncertainties even in the crosss section data used in simulations. There are also concerns with enhanced corrosion and MHD effects which inhibit heat transport in liquid blankets. Furthermore, the whole blanket system will need to be inside of the vacuum vessel which greatly complicates things.https://iopscience.iop.org/article/10.1088/1741-4326/abbf35/meta The most comprehensive review on the tritium fuel cycle came to the conclusion that it is nearly impossible to actually achieve a sufficient tritium breeding ratio, and the necessary technologies are decades away.The COLEX process, the only known process for isotopically separating out lithium-6 in sufficient quantities is effectively illegal in most of the world, since oak ridge ended up releasing 330 tons of liquid mercury into the environment when they were using it for weapons in the 50s and 60s and are still cleaning it up.
Why not just attach fusion reactors to fission reactors so you can use the fission reactor to generate tritium and then use that as your fuel in your fusion reactor?
>>16282424A 1 GW plant needs around 55 kg tritium per year, while fIssion reactors designed specifically to produce tritium produce less than 0.5 kg. So you’d need to build it attached to over 100 fission reactors
>>16282152you're missing my point - it's not that the ideas in isolation are bad, it's that they're incomplete and thus insufficient for solving the problems they intend to solve, and it's not for lack of knowledge but rather lack of attention, especially when completing those ideas has ALREADY demonstrated that current obsessions of the field (D-T) are untenable for simple reasons while the bulk of the work is being done on more computationally difficult but less useful problems specific to a COMPLETED D-T reactor. it's like doing fine grain ecosystem modeling for reintroducing Tyrannosaurus to a locale before you've even considered how to create a living example... and the geneticists are telling you it's literally impossible with every tool they'll likely have this century, even with huge advances. modeling those ecosystems might even be useful, but you shouldn't pretend it's the next step - and ESPECIALLY not that it is the NEXT-TO-LAST step - you need to take before recreating Jurassic Park.if any take is overwrought here, it's defending this habit. if the compsci experts call the code shit, it probably is. walled gardens are fucking retarded; reality doesn't wall itself off to insulate the ego of a single field expert when they're being retarded outside their limited scope of expertise - if the problem exceeds that scope (as, apparently, fusion power exceeds the scope of fusion researcher expertise), then the scope of their expertise is simply too limited to solve the problem, and in turn limited in its ability to even progress towards a solution coherently:the simple engineering reality is that D-D fusion is the only fuel cycle that's feasible, even in theoretical engineering designs. D-T fusion needs the reality of tritium to be different than what it is - you can't "iNnOvAtIoN" your way out of needing literal magic. muon fusion is even more overtly a rebuke of the simple realities of muons in service of an untenable solution, hence its pertinence.
>>16282467>build a couple terawatts worth of fission power plants>fuel a single 1 GW deuterium-tritium tokamak with the tritium>call it all fusion power>no public reeing over it since it's "clean fusion, not dirty fission"
>>16282573Someone put this man in charge of the DoE.
>>16282563I’m going to ignore the Jurassic park segue since that’s frankly distracting and irrelevant and be charitable but no, your point is clear. It’s just not relevant or as far as I’m aware even all that accurate. The ideas are of course incomplete. We haven’t achieved ignition in a meaningful way so of course they’re not handled. But what do you want? You’re complaining about physicists not having handled engineering problems and saying “that’s an engineering issue?” If the engineers find that a problem, they should find a new career since that’s exactly what their job demands. Also, the D-T fusion is being worked on already. Everyone knows this issue. Every idea of a fusion reactor that I’m aware of has in mind that they want to produce enough tritium to sustain the reaction with the reactor itself. There is also no walled garden. Fusion is heavily multidisciplinary. I don’t know what you’re talking about.As I’m also sure you’re aware, D-D reactions have issues of their own so I really don’t understand this complaint. It’s hardly as if everyone is ignorant of all of this. These are all well known issues and it’s not clear what you’re even proposing. Thinking up more ideas is exactly what needs to be done. It’s exactly how all problems are solved. Would you like people to just give up and stop thinking?
>>16282563>the simple engineering reality is that D-D fusion is the only fuel cycle that's feasible, even in theoretical engineering designs.It's not feasible, though. D-D fusion is far less likely to occur than D-T at any temperature we can achieve. If you take the Chinese data for the world record the highest temperature we've observed in a tokamak is something like 150 million degrees. D-D only has similar reactivity to D-T at something like 10 billion degrees. We probably would have better luck figuring out how to generate more tritium than trying to get our reactors 10 -100x hotter than the current world record.
>>16283287>I’m going to ignore the Jurassic park segueit's an analogy, not a segue, and you're again missing the point - it's not even about ignition.i'll boil the whole history of this down for you: initial fusion interest was powered by the abundance of deuterium, but on inertia from that hype and through efforts to "keep the dream alive" in the wake of the difficulty of D-D ignition, theoretical and putative experimental work congealed around designs for a fuel that is easier to ignite but currently LITERALLY impossible to obtain at scale, barring the "lithium blanket + active fusion gas sorting" gamble defeating the inconvenient conclusions of materials science. they abandoned the fusion problem of harder ignition with an abundant fuel for a whole suite of problems from non-fusion fields that they can helpfully ignore until AFTER they achieve D-T ignition.>If the engineers find that a problemthey are expected, by theorists and the hyped (and, evidently, yourself), to engineer systems unconstrained by realities that hype wishes to ignore. it's not going to happen, and not their actual job.>no walled gardenbeing interdisciplinary doesn't mean there aren't still walls (see: ignoring conclusions of materials science). there's also a wall between practical considerations and academic ones - not always directly a problem, but when theorists are promising a practical solution (i.e. a power plant), that wall makes their promises further from practical reality and thus further from truth. you even invoked that wall yourself with your little "that's the engineers' job" outburst.>produce enough tritium to sustain the reactionand this is precisely the part that has only vague and handwavey explanations, that have never been tested, and that have very discouraging results when modeled in detail (see >>16282292 for an example) that are simply ignored because the entire D-T plan falls apart unless the reality of tritium changes to what they've dreamed up for it.
>>16283721 (cont.)meant to reply to >>16283204>D-D reactions have issues >>16283287this is correct to some extent, but also not exactly the same kind of barrier - D-D doesn't require brand new imaginary technology to sort tritium, He-4, and He-3 from an active fusion gas feed continuously while also having the solid lithium blanket be able to sufficiently and SELECTIVELY release bred tritium into the fuel mix without deteriorating and adding problematic amounts of lithium to the fuel mix and disrupting the plasma conditions, and doing all of this with less energy than what can be extracted from the whole system. any aspect of that not working kills D-T at the feasibility step, which is what you do BEFORE the design step when creating a practical solution.with D-D, the barrier is ignition - a high barrier, yes, but there are proven ways to increase plasma temperature. they are difficult, but pass the feasibility test with flying colors compared to the feasibility test of the D-T fuel cycle.>Thinking up more ideasGOOD ideas, FEASIBLE ideas. not throwing shit at the wall just because you want volume - or because you can't figure out a feasible path for an idea you fell in love with before you fully understood how infeasible it actually was, and now you're just desperate.the good news here is that a 10-100x hotter temperature for D-D fusion is, while expensive, difficult, and, yes, still potentially impossible, a direction that has a clear path to feasibility (especially with a larger reactor - while a monumental effort, ITER isn't the biggest reactor it's possible to build; we're quite far from the engineering/materials science constraints of the largest reactors we can build).MCF research has become obsessed with achieving ignition above all else, including the original purpose of MCF - THAT is why everyone is so obsessed with D-T fusion. using it as an actual fuel was originally an afterthought, largely to fund D-T projects as power generation research.
>>16283721>they are expected, by theorists and the hyped (and, evidently, yourself), to engineer systems unconstrained by realities that hype wishes to ignore. it's not going to happen, and not their actual jobEvidently the ones who choose to work on it disagree.Some believe room temperature semiconductors are not possible to create. Others disagree. They either choose to work in the field or don't based on their belief about this. Either we get given conclusive proof this is unachievable (which you have not actually presented, only asserted), or it's well within reasonable expectation for a physicist to do the part that he can do (the physics), and leave the engineering to someone experienced in engineering, i.e. the engineer.>when theorists are promising a practical solution (i.e. a power plant)No theorist is doing this beyond hypemen like Michio Kaku. >this is precisely the part that has only vague and handwavey explanations, that have never been testedThis is precisely the point of developing new ideas and testing them with new experiments.I'll restate the question so we can get to the point:What do you actually want people to do? Do you want people to stop thinking about a topic you personally disagree with them on? Do you want physicists to stop thinking about physical problems (their job), because you personally have some issue with them not being involved with engineering work, which is a field outside of their job and which they are not at all trained to do effectively?>a high barrier, yesYou need to have temperatures higher by a factor of 10 before the D-D reactivity is even close to the D-T reactivity at 100 million degress, as I'm sure you're aware, and we do not currently have any ability to sustain temperatures of that sort. A challenge of that sort would no less difficult than sitting down and thinking about solutions to our tritium problem and it makes absolutely no sense not to pursue both based on people's professional opinions.
>D-D fusion isn't practical because its reaction cross-section is too small>D-T fusion isn't practical because we can't reliably source half the fuel>D-Dμ fusion isn't practical because we haven't solved efficient muon productionIt sounds like the common theme here is that practical fusion is a pipe dream.
>>16239982You can make fusors for 2-3k
>>16282424The only real advantage of a fusion reactor over fission is the comparatively low radioactivity, practically advanced fission reactors would be just as good in the eyes of the people who build power plants. There might be a use for fission-fusion hybrids if there is a need for super high neutron economies and it somehow works better than accelerator driven schemes but then again they can build breeders without that as well.
>>16282292Isn't ITER just a glorified physics experiment? They could probably utilize tritium much better in a practical power plant. And as for "The necessary technologies are decades away", a practical fusion power plant is decades away too so there is plenty of time to get COLEX unbanned and design a decent blanket.
>>16284314It's not achievable right now, yes. Of those three, I think muon-catalysed fusion is the only one that's really complete fantasy as of now. The others, you can see some kind of problem-solving pathway that could maybe get you there, even if the challenges are very difficult. It's not clear at all how to do anything with muons.
>>16284574MCF sounds like it could be practical as a neutron source since the reaction area can be pretty small and stuffed into something like a fission reactor, it doesn't need to reach breakeven if its just a neutron generator
>>16284565This is true only on the timescale of hundreds to thousands of years. Neutron irradiation of reactor materials would actually produce significantly more waste per energy produced than a fission reactor, even if you don’t include any of the tritium contamination. This is true even if you make as many components as possible with alloys specifically designed for low activation.https://iopscience.iop.org/article/10.1088/1741-4326/ac62f7/metahttps://scientific-publications.ukaea.uk/wp-content/uploads/GILBERT_2019_NUCL-_FUSION_59_076015.PDFhttps://library.psfc.mit.edu/catalog/reports/2020/20ja/20ja054/20ja054_full.pdf
>>16236530So after doing some reading on RF stuff, I think I finally get the idea of a matching network - the impedance of your plasma and the connected circuits varies with amplitude, frequency, phase, etc. and so the matching network is there to adjust things slightly to maximize how much power gets dumped into generating the plasma versus getting reflected back out into the circuit or something like that.But I still don't understand why you can't just use normal probes and shit. Is it like an interference thing? Does the RF fuck with the circuits or what?
>>16284909The potential between the probe and plasma is time varying, so it completely messes up the shape of the probe traces. Since current varies exponentially with voltage, it can’t even be fixed by time averaging and the result depends on the magnitude of the RF voltage. So you need some sort of circuit to compensate for the RF effects in the probe to filter out the AC current at the frequency of the power supply and its harmonics. There is also a frequency dependent capacitive voltage drop across the layer of contaminants on the probe tip which is hard to correct for.
