Cryopump

5 03 2009

Just won this cryopump auction

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17 responses

6 03 2009
A. McEvoy

This cryo might be too small to do very much, but backing up a good turbo it should do something at least.

You will mostly need a turbo/roughing pump combo that is capable of handling your 300+ L chamber. These can be quite pricey. I think it would be wise to calculate how big of a turbo you need based on what pressure you want to get down to. I would assume you want at least 10e-7 Torr and probably closer to 10e-8. At 300+ L, this will be a very big pump. Best of luck!

7 03 2009
M. Simon

I have done some calculations on turbopumps at IEC Fusion Technology.

I would avoid having any kind of diffusion pump in your system. One mistake and you have oil in your system. Oil that is very, very, very, hard to clean out.

BTW turbopumps are available at auction from time to time. Keep your eyes open.

Also note that the ultimate pressure possible with any pump is more a factor of system outgassing than pump capacity. Smaller pumps just take longer. However, outgassing is a fact of life. All I have ever heard from people who actually do this kind of work is “more and bigger pumps please”.

With the turbos you also need to look at the compression ratios for the gases involved. You may need a large pump (300 liter) followed by a smaller pump (10 liter) to get down to the pressures you want with the gases you are using.

You may also want to design your system so that it can be heated to 100 C or 150 C during pump down. That reduces operating out gassing. Such heating means demountable electronics.

7 03 2009
FAMULUS

It sounds like a turbo-molecular pump may or may not need a rough pump:

Turbomolecular blades cannot be built with anything close to such a small clearance, so this type of pump stalls if exhausted directly to the atmosphere. Nonetheless Varian, Inc. since 2006 offers a pump where the last stages have blades optimized for zero flow and can pump against a pressure of one atmosphere.

7 03 2009
7 03 2009
FAMULUS
7 03 2009
FAMULUS

What’s the “Foreline connection”. Is that connection facing the chamber or facing the exhaust?

7 03 2009
FAMULUS

HA. I just purchased this turbo-mol pump rather impulsively:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190286414349#ht_548wt_1155

9 03 2009
A. McEvoy

That is a hefty pump and probably will do the job. Doesn’t look like the auction included a control unit however, so you will have to do some digging for that. You will also want to replace the seals and bearings (hopefully just re-grease them) as it has probably not been used in a long time.

This turbo will need a roughing pump, and since roughing pumps aren’t tremendously expensive, I think that you should be able to find one for cheap, like the one you referenced on ebay. Not only does the roughing pump back the exhaust but you use it to pump down the chamber to the turbo-operating pressure regime.

9 03 2009
M. Simon

What’s the “Foreline connection”. Is that connection facing the chamber or facing the exhaust?

Facing the exhaust.

BTW since molecular pumping is a statistical process it is best if the inlet to the turbopump is connected directly to the reaction chamber with zero piping.

For safety a stainless screen over the pump inlet will reduce the chances that a dropped wrench will put you in the market for a new pump.

9 03 2009
M. Simon

Side note:

I have contacted Tom Ligon – the originator (along with Dr. Bussard) of the amateur fusor movement – about your project. I am keeping him up to date with your progress (he is very interested). He is on tap if you run into serious difficulties or have questions I can’t answer.

9 03 2009
M. Simon

Here is a product page for the 361 series. You can get technical details (like compression ratios for H2, He (similar to D2), and other gases.

http://www.oerlikon.com/ecomaXL/index.php?site=VACUUM_EN_online_shop

9 03 2009
9 03 2009
FAMULUS

M. Simon / A. McEvoy : Awesome. I can’t wait to get my hands dirty!

9 03 2009
FAMULUS
9 03 2009
9 03 2009
10 03 2009
A. McEvoy

The frequency converter is most like what I think you need for that pump, but I am not convinced that is THE one that you want. I would contact someone at Edwardsvacuum.com (parent company of Temescal) and see if they can dig up some info on that pump model. I don’t know if that converter is worth anything near $995 regardless…

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