In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.Subject: Re: Sorption and ion pump
Date: Jun 11, 4:58 pm
Poster: jim luxOn Jun 11, 4:58 pm, jim lux wrote:
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>Sorption pumps are great and are perhaps the best forepump, hvpump and uhv pumps around. I have seen three in a valved bank before with no other pump whatsoever in sight!! On small systems (like the fusor, a sorption pump of moderate size should do BETTER than any mechanical pump! Both in the depth of vacuum pulled and it is not just a matter of clean......., it is immaculate!!!!! you can beat them period!!
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>Again, have plenty of bread ready for LN2 and prepare for a gang o' trips to the welding supply house that pumps th' stuff.
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I was looking for some pumping volume (integral of speed) specs for a sorption pump. I found one that said 100 mTorr-liter per gram of 13A adsorbent. For a chamber some 12" in diameter (30 cm)(=4.5 l) to pump from say, 30 torr (easy with a cheap roughing "oilless" pump) down to perfect, you are looking at 135 torr-liter, or 1.35 kg of adsorbent.. Starts to look reasonable..
With decent insulation, your LN2 should last a while. The big storage dewars (GP45 type) run about 1-2% a day loss. Once you've cooled it, just make sure you keep it cool. LN2 is about $100 for 170 liters around here. And, if you are fortunate to work at a place that uses a lot, you can probably get a liter here and there for free...