Fusion Message Board

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 Pumps
Date: Jan 19, 2:50 pm
Poster: Pierce Nichols

On Jan 19, 2:50 pm, Pierce Nichols wrote:

>The bakeout cycle, I believe, has been discussed before here, but here goes again.

Ok, I must have missed it. Sorry for putting you to the trouble. Couple more questions:

>I assume that you know the down side of sorption pumps in that you must forever keep the pumps under LN2 even after valve off from the main chamber. This is especially true of the first pump in the manifold. If the pump which is sealed gets warm again, the outgassing sorbant can give rise to possible dangerous pressures. The other option is to open the forepump valve on the first pump, once the second pump is finished, valved off and the third pump is brought on line. At this time the LN2 bucket can be slipped off of the first sorption pump. Warming of the valved off second and third sorption pumps to room temp is not dangerous, as they have small amounts of contained gas compared to the first.

I noted that the commercial units all had release vents sealed by greased viton plugs. Looks like an easy enough precaution to take, and beats the stuffing out of aluminum shrapnel embedded in the walls of my garage.

>The aspirator is OK, I suppose, but it is limited by water's vapor pressure at any given temperature and water backstreaming might be a severe problem.

What about air aspirators? I wasn't planning on using a water aspirator for exactly the reasons you cite. In any case they are much much much cheaper than mechanical roughing pumps. While they can only go to about 20 torr, a sorption pump can take over from there and go deep.