Hello anons, I'm working on a project that requires a medium vacuum (about 10^-2 torr) and am looking for advice on where to even start and common pitfalls. Most of the stuff I find online is either for high/ultra high vacuum or shit-tier degassing setups. Do you guys have any good resources?
Kind of depends on your application - what are you looking to do?
>>16982132I'm working on a schizoproject that I don't really want to talk about because I will get told it's stupid. I need a high voltage passthrough and some sort of filter on the vacuum pump inlet.
>>16982116It should be easy to get that with just a scroll pump if the tip seals are new.
>>16982203>medium vacuum>high voltage>filter on vacuum pumpOkay, so you're trying to do something plasma physics-y and you expect to be introducing or producing materials you don't want to get sucked into the pump - possibly bits of probes/electrodes you're expecting to ablate, particles from sputtering, or chemical residue. I assume your schizo project is something fusion, material modification, or electric universe related. It probably is stupid, but you're on an anonymous south-Indonesian artisan cookie-baking forum and we've all had stupid ideas before, so I encourage you to share specifics if you're willing, and especially if it relates to expected experimental conditions that might result in safety concerns.If you understand the risks involved in this sort of DIY project, read on for my general DIY plasma advice.If you don't want to go aluminum or stainless for the body of the chamber, consider thick-wall acrylic (>3/8" thickness). borosilicate (Pyrex) is a good option as well, but it's hard to find stuff thick enough to use safely. the common rig for degassing setups (stainless steel bucket with a 1/2" to 1" thick acrylic lid) actually isn't a bad option here. A decent electric rotary vane pump from Harbor Freight or wherever is good enough to get you down to a low-to-medium baseline vacuum, especially if your chamber is on the smaller side. The acrylic is good for drilling and threading bits for gas, vacuum, and feedthrough access - slap an O-ring between the bucket and the lid and you'll get a decent seal.Acrylic's not bad for holding a vacuum, I use them as a material for cheap viewing windows on higher vacuum experiments because they're easy to machine into shapes compatible with standard ASA and ISOK flanges. Outgassing (gradual release of gases adsorbed by the plastic material in atmospheric pressure) isn't really a concern at the pressures you're planning to operate in, either.
>>16982484For high voltage, the main pitfalls are shielding, grounding, and stability. Shielding and grounding are mostly safety issues, you want every piece of your chamber and your power supply to be properly shielded and grounded to avoid getting zapped or zapping your other components. Other than that, your choice of high voltage source depends on what you're doing.If you just need arcing, anything with a simply flyback transformer will do, for plasma demos I use in class or take to outreach talks, my favorite DIY choice is pulling the guts out of a plasma lighter - ten bucks gets you a USB-chargeable switching source that'll output at least 5 kV. You can connect the leads to electrodes and get yourself a poor man's switching source. These run at constant voltage so they won't produce stable discharges, but they'll last a few seconds at a time. This is my preferred option because the discharge you get is very-low power which means even if you fuck up, your risk of damage or harm is negligible. However, if you need a nice, stable glow discharge you need something that will run in constant current/power mode. Standard fluorescent sign ballasts are a good option there, they're affordable, will get you to the voltages you need and then drop into a constant current mode when it hits breakdown, and have fault protections and other safety features - but even so, be extremely careful running anything high voltage and run off mains. Under no circumstances use older or sketchier shit like neon sign or microwave oven transformers - these can generate plasmas, but they almost completely lacking in safety features and are notorious for frying DIYers.For filters, I assume you're dealing with particles or residue that you don't want getting into the pump. A fine mesh cut to shape and welded or adhered between some metal rings or something could work if they're made to a size that can fit over the vacuum intake without getting pulled in.
>>16982203High voltage as in “needs a SHV connector” or high voltage as in “needs oil/SF6 and a vacuum insulator stack”?
>>16982484I understand the risks of this sort of project, I've been doing high voltage stuff for years and am excited to finally have the money to dip my toes in a vacuum project. I do need to see the inside though. On the topic of the vacuum, what connectors work and what sort of tubing do I use? I'm also looking to get a pirani gauge for it and found one on ebay, but it has one of those KF connectors. Should all my connectors be KF? Are there common pitfalls that I'm going to run into and scream and cry?>>16982489>>16982561It will be between 10 and 30kV and extremely low current. My plan was to just feed wires through and hook it up to the apparatus in the chamber. Is that going to cause problems? It's an idea for additive manufacturing I had, and there are going to be metal particles on the order of 1 micron being produced. I have a plan on how to filter them once the vacuum has been pulled all the way down, but while it's being pumped I'm worried they will get into the pump and break everything. I actually want to avoid glow discharge or other plasma phenomenon. A interesting note that I didn't mention previously is that I am considering placing a servo in the chamber. Is that going to cause problems? What would be the best 3d-printing filament for placing in the vacuum?
>>16982570>My plan was to just feed wires through and hook it up to the apparatus in the chamber. Is that going to cause problems?I haven't done anything with vacuum but I am an electrician that has had liquids drawn up a cable under the insulation.I would recommend running bare solid copper wires through the acrylic so you don't get leaks though the cables. If you are experinaced with HV you know the risks and how to minimize them.
>>16982570If you're just looking to do simple stuff, KF/CF/ASA flanges are largely unnecessary, you can get away with drilling holes in the acrylic viewport and inserting threaded MPT ports for your gas and vacuum lines. You can also get away with vacuum gauges using those same threads although if you have your eye on a particular gauge there are very simple MPT to KF flanges you can buy online (some Chinese companies sell quick, cheap, and dirty flanges and bellows and shit which will do in a pinch for medium vacuum territory).>It will be between 10 and 30kV and extremely low currentHow low do you think "extremely low current" is? Because I'm imagining nano to micro amps.
There are youtubers who do diy replication of serious experiments. They sometimes have a vacuum setup. I remember one discussing it in detail, e.g. he had to use special bolts with slits so that air doesn't get trapped in them. Search there.
>>16982570You won't easily find a filter for particles that small without it being impossible to pump through. The smallest mesh ones are 250 microns. I think the pumps can survive without one.High voltage feedthroughs aren't very expensive https://www.lesker.com/feedthroughs/power-feedthroughs/part/eft3013098b and are also easy to make (pic related). >>16982583 is correct that you need a solid conductor to avoid leaks.At vacuum levels that bad, connectors almost don't matter, and neither do the materials you use. The servo should also be fine even with standard oil or grease lubricant. Solid graphite lubricants become abrasive under vacuum.>>16982665Avoiding blind holes is almost always better than using vented bolts, either way it isn't necessary at pressures this high.
>>16984542He could build an electrostatic trap, try to keep any particles generated in the main part of the chamber. It won't do much to stop stuff from getting sucked in if you suddenly turn the vacuum on and let air pressure suck shit up, but in vacuum conditions it might be enough.
>>16984542This. You can get away with a LOT of shit at these kinds of vacuum pressures. It’s only UHV conditions where a lot of this outgassing and surface condition stuff and special seals and gaskets and shit become important. I’ve got a plasma demo I do for my students and the setup is literally just a thick acrylic cylinder with two thick acrylic disks I milled to put a rubber gasket on as the caps, and two metal gas valves I took from an old lab room threaded through the bottom with some fucking teflon tape on the threads. My electrode feedthroughs are just some holes with aluminum rods stuck through that go to a pair of disk electrodes and some cheap vacuum epoxy coating the point where the rods go in. Gets down to 3-4 Pa, no problem with a little electric pump and I just use a fluorescent light ballast for a source. Whole setup was like $200 when I made it.>>16985374I’ve seen dusty plasma guys do this kind of shit all the time - put a couple of ring electrodes and not the chamber and hook the up to a low voltage source and you can get a nice trapping potential for any particles in the chamber.
>>16985722>electrodes into the chamber and hook them up to a low voltage sourceFuck you, autocorrect.
