Chamber design?.....

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Quantum
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Chamber design?.....

Post by Quantum » Mon Aug 31, 2009 12:26 pm

Having now reached the point where I'm starting to design a chamber, the four main questions seem to be: size? shape? number of ports? size of ports?

As I'm planning to use the chamber for other purposes besides fusoring, I want something fairly large, certainly larger than 12 inches (300 mm).

Cylindrical would be easier to construct, but does have some limitations if you want a large number of ports aligned with the centre, so spherical seems the logical choice.

It makes sense to add more ports than you will ever need, (although I would expect a lot of people would say 'the fewer ports, the better')

Ports obviously need to be large enough, and, as I'm planning to construct the shell from flat plate, larger ports mean less compound curvature is required in the plates, (This will be the biggest challenge, as I see it.)

No automated/CNC equipment will be used. No large presses will be used. It will effectively be 'made by hand'.

I've come up with a preliminary design for an 18 inch (500 mm) spherical chamber, with 6 x 8 inch (200 mm) ports, (10" conflats) and 8 x 2 3/4 inch (70 mm) ports (4 1/2" conflats), with a shell thickness of (nominally) 1/8" (3.2 mm). This will be decreased a bit by compound curvature/grinding). The chamber will be electro-polished inside and out.

As the chamber will have surface area of ~1000 square inches, total pressure on the chamber will be around 7.5 ton.

I've included an image of the basic layout of the proposed design below.

Any comments/suggestions/feedback will be appreciated.
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Doug Coulter
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Re: Chamber design?.....

Post by Doug Coulter » Mon Aug 31, 2009 1:51 pm

Ash,
What you have pictured here is a good design -- and available at Lesker as a stock item, so a few people think so.

You can get plenty of things pointed at the center of a cylinder too, though. The tank I acquired surplus has quite a few, though some are different distances from center and angled in, in addition to all the ones that either circle another "center" and the stuff that is around the bottom periphery. I bring my evapration heat leads and thermocouples from those on the bottom and so don't have to take them out to run the fusor I do in a side arm in this one.

The main problem with the big tank is the one 6" door -- there's a lot of tank in there to only be accessed that way, what I call the "ship in a bottle problem". Your design would be better in that regard, but it you want a nice hinged door to get into it with, the price is going to shock you.

Being able to get at least one hand into the tank while looking through a window is necessary, getting two hands in there (preferably from opposite sides ) is VERY nice. For a lot of things, where you can tolerate the seep through of viton, you may want to consider using opposing big flanges as doors you can get into and out of quick, with another one as a window so you can see your hands and the work.

A smaller cylindrical tank in the background is a lot better access. It's a 6" ID Tee, with a bunch of flanges welded on to point at the center. In that one, the whole back comes off with only a few bolts, and the window is also removable, so you can get at things from both ends. Those are viton sealed, so it's fast, easy and cheap to get in and out of. Assuming one can tolerate that much viton, it's the way to go. It has 4 additional 2.75" conflats welded on that either point to center or come in from below for evap power and so on. We fabbed a SS screen on the bottom port of the Tee that goes to the vacuum system so the field in the tank is pretty uniform in fusor mode.

Both are useful -- which I use for something depends on other factors. The Tee tank is diff pumped and therefore tolerates dirty processes better than the clean big tank with the turbo. Both have done evaporation and fusors. But I wouldn't do some kinds of say, reactive sputtering, or buckyball making in the big clean tank -- that one wants to stay clean as a reference. I have another cylindrical tank elsewhere that's also turbo pumped, long and skinny (6" by 30") and it's also useful. I ringed the circumference of that one with a few sets of 2.75" CF flanges at various points along the length, and use that one for fooling with particle beams (the long aspect is nice for that).

So, different strokes -- might be wise to plan on a standard size attachment to the vacuum pumps, as you may want to accumulate other main tanks sometime down the road for doing different things.
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Quantum
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Re: Chamber design?.....

Post by Quantum » Mon Aug 31, 2009 3:16 pm

That's a very nice tank, Doug.

I may still go that route myself. One reason I'm trying to avoid internal 'corners' is that they are more difficult to electropolish. another is the increased volume inside the tank.

I imagine four large and four small ports around the centre of a cylindrical tank would be sufficient,

This is also the main disadvantage of a large 'Tee', where the extra volume is considerable, along with, presumably, three very large ports.(and three very large seals)

The main advantage of the Lesker design is that you can use bolts with nuts, rather than threaded holes. (Not much room for a helicoil in a conflat), Lesker also use a 3/16 shell on their's.

I'd considered fitting 'extension tubes' either side of my design for any 'linear' stuff, and for 'manipulators', if required.

A vertical cylinder may be the best way to go. Overcoming the electropolishing issues may be simpler than producing compound curves in 3/16 stainless plate.

I'd assumed a diff pump wouldn't be suitable for sputtering, etc., due to oil contamination. Is this not a problem?

I imagine a filter that prevented oil contamination would hamper high vacuums.

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Re: Chamber design?.....

Post by gamempire » Tue Oct 13, 2009 2:34 am

Hi Ash,

You mentioned that you'd be using your chamber for other things, which definitely helps justifying the time and/or cost in getting a nice vacuum chamber. As my fusion project has started to come to a close for the time being as I'm now in grad school, I've been starting to work on some new plasma physics stuff with several professors, using all the wonderful equipment from my project.

viewtopic.php?f=6&t=2846#p12356

You can see some of the pictures of my spherical vacuum chamber there. One of my biggest regrets was not going with a few larger CF ports (6" and 8"), and just using adapters where needed. Its much easier to mount my grid using a barrel connector onto my HV feedthrough and then insert the entire piece into the system, but few grids will fit through the opening of a 4.5" CF.

The other thing you have to worry about is mounting of the chamber. The original way mine was setup is attached below. I will tell you, with a chamber that weighs over 120 pounds, its not fun when you have to open it up along the horizontal axis while having to disconnect it from the pump as well. There is a 13.25" conflat on the axis, and I used a copper gasket in the begining. But after the 2nd time opening that, I kind of got fed up with the price of a 13.25" gasket, and just bought a viton gasket to use in stead. I haven't had any problems in the range pressure range of fusor operation, so you should be fine for using them on the larger seals (I'd still use copper when you can for the smaller ports).

About a week ago I started construction on a vertical mount for the chamber. Lesker has a picture on their website for mounting spherical chamber's that I've attached as well. Basically, for my stand, each of the 4 arms will connected to 3 of the bolts on the center conflat to hold it aloft.

Feel free to ping me if you have any questions.

-Josh
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Re: Chamber design?.....

Post by Quantum » Wed Oct 14, 2009 8:01 pm

Josh, I've also had to put my project on hold as I've landed a job with a world leader of vapour deposition and ion etch machines, and I'm working away from home.

While mine will have conflat (CF) flanges, I'll also use viton seals when I can.

Mine won't split in the middle, but will have 8 inch ports. It won;t have stalks, mainly due to electro-polishing issues, but these can be bolted on if required.

I'll probably weld mountings to the shell (well, mounting points, anyway)

By the way, we use a lot of aluminium chambers with viton seals at work, especially for atomic layer deposition machines (which initially surprised me) We also use a lot of rectangular stainless chambers, but these tend to have very large turbo pumps.

For high temperature work or for ultra high vacuum work I believe you do need copper or silver plated copper gaskets.

Also, aluminium chambers can't be used much over 400 degrees C.(Although some of our aluminium chambers do have 700 or 800 degree C 'tables')

By the way, we use gold plated gaskets too, and solid 24 karat gold gaskets for some corrosive processes.

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Doug Coulter
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Re: Chamber design?.....

Post by Doug Coulter » Wed Oct 14, 2009 8:32 pm

I see some nice things here. I own the twin of that small Pfeiffer pump station, and love it. I use it to test some things before putting them on a bigger systemm, and added a tee off it to do things like making glow tubes and pumping down tanks to transfer D into without the air in there first. With a small tank, it's the ideal hobby fusor system in my opinion. No diff pump waiting, accidents with inrush pushing diffoil into the backing pump, comes down fast and clean with an IR bakeout source in the tank, just a sweet thing.

We handled the Tee field-funny by putting a SS screen over the leg that points down to the pumps to get a uniform cylindrical field. As I'm working mostly with cylindrical grids here, that's what I wanted anyway.

And, in a test I did, with a cylindrical grid at an odd angle in the big tank, I got a spherical ray pattern anyway (I was testing a new HV feedthrough design but hey, why not put a grid on it?). This with a cylindrical vane grid at a 45 deg angle to everything. This implies, as I've said before, that the applied field is far from the whole story anyway -- I should have seen influence from tank shape, but did not.

Electro-polishing works no matter the shape of the thing -- I do that here all the time. I get my basic materials in that state anyway, and just clean up the welds by the good old elbow grease method. That kind of thing is mainly important for real high vacuums (eg better than e-9 mbar), or real high field uniformity, neither of which you're going to have in even the sphere design with all those holes in the sphere, unless you take some fairly extreme other measures. No one here is doing that, and to the extent I have, it didn't make squat difference to operating fusors.

You can do sputtering and evap with a diff pump, we've done it here with fine success, but again, we're not trying to put a billion transistors on a chip either. For most uses, a diff pump with a trap, or the expensive oil does fine. In fact, for most uses, a cold water trap and diffoil-20 is fine.

As some other posters have mentioned (and not just this thread), it sure is nice to be able to take the thing down fast to try new things -- and get back to vacuum quick too. Though I have a lot of respect for what, for example (sorry Andrew) Seltzman has done, it smacks of technical hubris to me to assume I can make something that hard to work on and get anywhere fast with it as I learn new things I want to try -- which may not fit in the nice looking, neat and compact apparatus one initially envisions. That's putting what I think rather mildly. The T with both ends coming off with 8 total bolts is the one we try most new things in, as it's the easiest to get into and out of, and rates as the better thing for most of our experiments where the diff pump limitations aren't a big deal.
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Re: Chamber design?.....

Post by Quantum » Thu Oct 15, 2009 9:23 pm

Doug, electropolishing of complicated shapes is extremely difficult. In order to get even electropolishing you need an even current density, but current takes the path of least resistance. Therefore, electropolishing of internal corners is not easy.

At work we only use turbo pumps for vapour deposition and ion etching. Diff pumps would be a lot cheaper. You have stated in other threads that your attempts at sputtering were not that successful.

There is nothing wrong with cylindrical or box shaped chambers for most applications (we use them at work) but spherical chambers are easier to electropolish and have minimum surface area to volume ratio.(fusors have been built out of pickle jars).

Unfortunately, I've had to put my project on hold while I'm working away (I may get 'laid off' in a month or so) but the experience I'm getting working for a world leader in plasma technology is invaluable, priceless even. I'm hoping to make some more progress on my own project over the winter period.

first will be constructing some BIG heatsinks (fan cooled) for the BIG diodes for my mark 2 rectifier (which I will use for DC welding as well as electropolishing) along with working on my high voltage power supply and starting on my chamber.

While the machines we build at work are exclusively for the semi-conductor industry, and cost around a quarter of a million to half a million US (individually, not 'clustered'), I'm aiming to build my system for around one percent of this price.(certainly only a few percent).

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Re: Chamber design?.....

Post by Doug Coulter » Fri Oct 16, 2009 1:24 am

Ash,
I've done pro electropolishing for quite a few years, with pro solutions that have decent "throwing power" and it's a lot easier than electroplating, which is also a business setup I own and do regularly, and which is much tougher, frankly. There are no inside corners in your design as shown, and anyway "even" matters how? If part of your .1" thick SS walls are 1 mil thinner, do you actually care as long as it's all smooth? If you're taking off even a mil, you didn't do something right in your prep, a whole mil roughness is far worse than what I start with here. Even straight off the lathe or mill.

You don't need to do the whole tank at one time, you know, you can do pieces with a formed lead cathode and a little solution puddle if you want to get that fancy -- and you'll only need a cheap switcher supply (surplus) to provide the current, nothing special at all (this varies with solution composition, some will run fine at pretty low amps/sq). I think, no need. I just clean up the welds and let it go at that, but I do buy some big stuff polished already, because it comes that way and it's pretty. If you want cheap and fast, just evap or sputter something nice (say Ti or Al, or even gold is cheap at micro-inch thickness) over the rough SS. It's actually hard to avoid under some circumstances anyway -- it's what you're going to have like it or not, unless you take precautions. Hot ions on metal will re-sputter everything on the tank walls at any rate, despite what's underneath. (and your insulators and windows, unless you protect them)

In reality, you only even need this if you're pushing e-8 mbar and (way) below, and having to get there fast. Your fusor will run e-2 or e-3 range, so 100 times less than that for basic purity is still only e-5 or so -- a good system will hold that overnight with the pump *off* after outgassing, and almost any decent high vacuum pump (diff or turbo) will get you there in two minutes tops (plus the warmup time of the diff pump, if used). Sputtering runs in the same region as fusors do, with some fudge depending on the process details (plain,reactive, atomic layer deposition etc).

So, still no need for EP. Just make it clean and smooth the old fashioned ways.
And if you want to gild your lilly, get out the phosphoric, sulfuric and citric acids and polish away.
50 ppm or so chloride ion helps a little bit, as does a tiny bit of something like polyethylene glycol.

Now, as someone who pays a payroll, and considering the other costs of semi manufacture you mention -- the people cost more than the gear, by quite a bit. Anything the cuts yield is a very big deal even a pointy headed MBA understands, so -- no risk, kick out the diff pumps, and their maintenence and contamination accidents. Save even *one* time of expensive people standing around while one has to wash a very complex "dish" due to backstreaming accident, and the turbo is better than free -- in that situation. Here I find just the time to get back to good vacuum faster and with less complexity for the operator alone is worth that -- and so do they as it happens every time you run the process -- save thirty minutes a day for a whole team? No brainer. I love turbos, but it's because of speed and convenience, purity comes along for the ride, not that I mind that either. I like to add *known amounts and types* of that for testing their effect, not wondering instead if I've got a problem or a good result due to that factor I can't control.

I never said I had trouble with sputtering (though I've not done transistors, and want to someday), only that I'd fried a couple permanent magnets trying to duplicate the pro stuff on the cheap, without cooling -- easy to hit the curie point in vacuum. And I did all my deliberate sputtering testing with just a mech pump, oil type, no other pump needed (it was and is a good mech pump and a tight system). Sputtering works all too well, frankly, as in today I had to pull out my uWave ion source tube and clean sputtered copper from the ion extraction electrode off the quartz tube to get it working again (gun cleaning copper remover worked great to remove the pretty Cu mirror). Replaced it with Mg, which doesn't sputter so fast. Sputtering works fine without magnets too -- but you don't get even target utilization, important again if you're paying big money for the targets, and far more (as is the normal case) for the guy who changes it out and re-qualifies the system on the new one. And paying the guy who keeps them in stock and so forth.

They spend those big bucks on the gear, because, believe it or not, the people cost even more, and getting more out of them with mere toolage is the cheapest way. Ask any big company that makes stuff, like the ones I spent the last few decades doing product design for (and developing that same gear as a sideline to help them make even more money to pay me with).

Many people think that their take home pay is what they cost an employer. When you *are* one, you'll know better. Try more like 3x that, at the minimum. Bennies, SS taxes, unemployment tax, disability insurance tax, paid time off, and a few other things add up kind of fast. And oh yea, the paperwork you have to do when you employ someone -- and make sure they have what they need to do their job instead of standing around doing nothing (or worse yet, distracting someone else) while getting paid. And rent/tax on the space they work in, and on and on and on. People aren't the cheap part -- look at the economy now, are we looking at big companies laying off mainly buildings and gear, or people, to save money?

A hobbyist can afford to think of their time as free (and many do and use that to "cheat" when they say how cheap things are -- but even a hobbyist pays rent, eats, drives a car and so on, and so even that free time has a cost, as does driving to 20 hamfests to make one good score and several bad ones not figured into cost), and this balances the equation a lot differently for them. A hobbyist may decide to spend extra time polishing something by hand, that a business would never do -- they pay some guy, which costs a lot more than the sandpaper does -- that's in the noise for them. So, it's natural for a hobbyist to substitute his time for money, as he often has more of the time than the money. Not that it's actually cheaper if you could be getting paid for that same time, then just buying your solution with that money. This is something people here tend not to be real rational about, so, flames on. And of course, it's always a question of balance. Buying even cheap surplus solutions when you don't understand the magic and can't fix them is a false savings in my eyes -- it gets most when the stuff breaks and they can't do anything about it.

I am finding, at the limit, that there's even more to it than that. For example, I'm having troubles with HV feedthroughs when they are hit by hot ions (they get conductive due to chemical reduction and sputtering onto them). None on the market, even the multithousand dollar ones, solve this, really -- their tank sides are poorly designed to handle hot ions in a not-high vacuum. They all have a thin spot that breaks down even when used well under ratings, after a certain time when hit by hot D+. It would cost more than my lathe did to have one custom made that addresses this issue -- and if it doesn't, I'm out the money, but not the problem. But instead, I bought the lathe (way back), and spent a couple tens of hours working out and making and testing a design that solves this one. This is only about the 20th time that investment has paid for itself, in hobby mode alone. Even if I charged my usual time rate to the project (high 6 figs/yr), I'm still ahead.

So, any good engineer is a guy who can do for a nickel what "any fool can do for a dollar".
If you're honest about all the dollars, and know how to do trade offs, different strokes all can be valid for the same set of issues, in different circumstances. Just learn to be honest about the *true* costs of everything involved, it's eye opening.

Even your own time is expensive -- so a little extra work on tank design to make it easy to change things so you can follow your nose is well worth it. Unless you just want to copy someone else.
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Re: Chamber design?.....

Post by Quantum » Sat Oct 17, 2009 12:00 pm

Doug, I agree with everything you've said.

The reason my tank is of that design is to make it easy to electropolish.

I understood that you'd had some problems sputtering TiN, that the coating was brittle. I remember John Futter suggesting annealing after sputtering to cure this. I undersood you may also have hed some cintamination issues, maybe this wasn't the case.

I appreciate your points about electropolishing, and agree with them.

Glycerine works in place of ethylene glycol.

The point I was making is that I wish to avoid 'corners'.

I also agree with your points regarding diff pumps and backstreaming issues. And the man-hours required to rectify 'accidents'.

While I appreciate that UHV is not required for either sputtering od d-d fusion, I wish top use my chamber for other purposes too, and also wish to construct it 'to he best of my ability' as a pro metalworker.

If I ever get around to experimenting with proton guns and solid B11 targets, I'm assuming I'll need UHV.

As always, I appreciate your comments, Doug.

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Re: Chamber design?.....

Post by Doug Coulter » Sun Oct 18, 2009 1:10 am

Yes, the metalworking on these can be fun, if you like that kind of thing (I do, and now even make my own flanges and feed throughs now, as well as other easier things). I find that good design for buildability is important -- a design that looks good on paper but makes you do welding through a small hole blind isn't so hot. It's a good move to map out all the steps at least in your head before finalizing a design and buying materials!

I've used glycerin too, but it costs more, and pure glycerin has other interesting uses around here (things that go bang ;~). I've actually found that a number of organics in small amounts help, but didn't write down the mish mash I made up. At one point I tried like 5-6 formulas from patents, and didn't get quite what I wanted out of any of them, so I mixed them together prior to dumping them on some poison ivy (good use of old chemicals out here in the boonies if you use discretion) and just for fun, tried the mix. It was the best yet!

I mostly sputtered pure metals as that was my interest then. I've done darn little work with reactive sputtering like you do for TiN. I've made some TiH or so it appears, it's really pretty -- this is because I use Ti grids on the fusor and that's what winds up on tank walls. Probably useless except as a gas buffer in a fusor, and a pain when it gets all over the insulators. Next sputtering I do with be with ITO for some fun projects around things that conduct electricity but pass light. For now, I'm mainly evaping and using Al, Ti, and Au, and will move to Ag soon for something (a borehole DT target design).

I finally did a FT design that uses quartz (preferably) or pyrex tubing(s) in a coupler for the insulator, so you can yank it easily and acid clean it when that happens. Once the details were worked out (I'll post on this later on), it's pretty sweet -- and beats paying for a new feed through if you whack one at the ceramic/tank junction (where the ones I've messed up die -- once they arc through there once, it's over, pretty much, and a little sputtering from the grid makes this happen if you don't keep after it).

If you haven't yet, do get the *free* Kurt J Lesker catalog. I'm not saying buy things there (but I do sometimes) but this catalog is probably the best book on vacuum technique, short and sweet, out there -- after they get those prices, they want the stuff to work for you so they keep the money with no support hassles. They cover a bunch of the things you're interested in. The price is right, the knowledge will save you endless money and work -- and I've checked most of it here, and it's the straight skinny all the way. It is a little biased toward using their stuff instead of homebrew, for the reasons we know -- most of their customers are for-profit and need speed and reliability.

People's definitions of :high" and "ultra high" vacuum tend to be a little blurry depending on where they are coming from (application wise).

What I use, especially for beam type work, is mean free path. Heck, if it's big enough to get a beam without a lot of scatter (or accidental glow discharges etc), you're there. You don't need a mean free path of kilometers for virtually anything -- What lesker defines as UHV IIRC is basically lower than e-9 or e-10mbar, which is pretty tough to get in any chamber you open once in awhile. And it takes a lot of patience in baking and waiting and waiting (followed by yet more waiting), usually sub/ion pumps and getters on top of the turbo and so forth, and is even pretty hard to measure with most gages you can actually get your hands on. The big boys of course add cryo to all that pumping. Too much for the home IMO. (I live a long way from anywhere you can even get cryo liquids).

I've been doing electron and D beams here, and happy anytime I break below e-7 mbar, and actually have good success at higher pressures -- roughly e-5 mbar has a mean free path of about 650 cm -- even a mass spectrometer with a fairly long path and very low energies works fine there with little scattering (but not much above that). So you can do this stuff even with some viton seals if your pump is good. (think saving money, you can reuse the viton more times than a CF copper gasket). Just keep the amount of it low, only use it on the stuff you have to open a lot.

In other words, with a decent turbo or diff pump plus trap, and even with viton seals here and there, it's not hard, and you get there fast (overnight without baking at all if the tank is basically clean), maybe two hours max with baking -- one hour bake, one hour cool down. That's coming down from dirty/humid shop air, if I bring the tank up with argon and work fast (eg don't let a lot of air in there) it comes down much faster. I've seen e-9 mbar in the big system which does have viton seals for a couple of tubing couplers and the big door, but I don't see it often. If I've just evaped Al or Ti, I see it all the time -- either makes a good getter. The trouble of course, is that it's like putting a bullet into a can of spray paint -- it takes good shielding in there to keep the stuff from getting all over the tank (which is fine for me) and the insulators (not good at all). I use a second window inside the main door window to catch crap, which then can be acid dipped to make it clear again. Can't do that with the expensive window/door, so it's a good system. I also use a mica shield on some systems, for the same reasons -- they protect the main window nicely and are disposable-cheap.

So, I'd say that dreaming of "real" UHV, like e-10 or better mbar, is something you custom build a single system for -- it's a whole new world, much harder, and rarely needed for anything. You see that in e microscopes that use field emission, and surface contamination studies, not much else, or beam lines that are kM long -- when you get there, will you hire me?

Re, the priceless education -- get all you can, it's indeed priceless and pays of over and over through life.
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