This pump look good?

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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jrhunger
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This pump look good?

Post by jrhunger » Wed Aug 04, 2010 4:01 pm

I am looking to build a demo fusor, that in the future will be beefed up to a true fusor. If I get this pump will it be enough for a demo fusor, if I am using this as a power source.

http://cgi.ebay.com/3CFM-VACUUM-PUMP-11 ... 078wt_1137

http://cgi.ebay.com/15KV-30mA-110vac-Ne ... 451wt_1158

Nicker
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Re: This pump look good?

Post by Nicker » Wed Aug 04, 2010 5:18 pm

For the pump I would look for something with a KF fitting.

Price-wise, I'm sure you can get better quality of both items for cheaper, used.

tligon
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Re: This pump look good?

Post by tligon » Wed Aug 04, 2010 5:39 pm

The ultimate pressure specified on that pump is 25 microns. That is not quite good enough to get a fusor into its optimum range. It is good enough to get a plasma.

I've been eyeing those cheap 2-stage rotary vane vacuum pumps on e-bay for a while, wondering if they might actually pump down better than advertised. The price is certainly attractive, and there are two-stage high speed rotary pumps that do the job nicely (I own one that will pull 2 microns). It could simply be that 25 microns is a number refrigeration technicians look for ... these pumps are aimed at the refrigeration service market. That may be the ultimate pressure they typically attain when sucking a freon system dry.

If you are willing to risk it, I'd love to hear how it turns out.

The 30 mA NST is a little on the weak side, but it will make a nice trainer. It is relatively unlikely to kill you and it will make a glow. 60 mA would be nice if you can score one (mine came from a dumpster). Have you found a source of high voltage diodes yet? I've seen some that would do the job in microwave oven parts catalogs (you would need 2-3 in series).

dbrown
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Re: This pump look good?

Post by dbrown » Wed Aug 04, 2010 9:51 pm

E-bay has two stage heavy duty pumps (they really do suck!) that can be had for somewhat more but it will get down to a few microns and have a huge pumping speed (you will need to clean and replace the oil.) As for a power supply, that looks kinda useless and I've seen flyback transformers that are cheaper and offer higher voltage and have somewhat similar overall power rating and again - e-bay. High voltage diodes (15 kV, 1 amp) are cheap and avilable on e-bay, too. I got mine from there.

A web site shows how to use a 15 kV neon sign transformer with Cockcroft Walton Multiplier create a 63 kV supply - that should work:
http://users.tm.net/lapointe/Cockcroft_Walton.htm

tligon
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Re: This pump look good?

Post by tligon » Wed Aug 04, 2010 11:30 pm

You might get 63 kV out of a doctored NST, but if it is only a 15 kV 30 mA unit it still will be seriously underpowered. There would be so little current behind it I don't see how it would work well.

My 15 kV 60 mA unit, modestly overdriven on the primary, can theoretically put out 13 kV peak DC, but it loads down below 10 kV with any plasma glow at all. It probably is able to produce a trace of fusion from head-on collisions, but not with any statistical margin above background. I still use that transformer, but for non-fusion public demonstrations of the basic operation.

My strategy was to tap in to the EMC2 power supplies (at the time, three 20 kV 1.1A units), which produced a satisfying count rate at 18 kV and anywhere from 5 to 25 mA. Anything less than that is training wheels. So lurking on e-bay waiting for a good deal on a nice HV supply with sufficient voltage and current is worthwhile.

Same with the pump. There were a pair of Welch 1402's on yesterday or the day before, eight minutes to go on the auction, and the more expensive one was sitting at $128. They might have possibly needed a little work, but those pumps are ubiquitous and the rebuild kits are easily available if anything is wrong.

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