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: Teflon Coating/Capacitance Manometer
Date: Jan 17, 10:25 pm
Poster: Richard Hester

On Jan 17, 10:25 pm, Richard Hester wrote:

A good point - sounds like something one should do as a matter of course to avoid heating up the pump connections. Since the flange I'm thinking of using for pumpout is on the end of a 3-4" side arm, it shouldn't be too hard to screen.
For folks setting up their own systems, if the side arms for pumping are attached at an angle, then errant beams wouldn't get too far inside... This is a bit more of a pain than having them stick straight out, and maybe not quite as good from a conductance standpoint, but may be worthwhile to avoid splattering electrons on valve innards and joints.

BTW, You mention setting up a capacitance manometer for your new system - which one did you find? I've seen both MKS and Edwards units as surplus. Duniway stocks the Varian units new, and offers reconditioned MKS sensors and readouts. Johnstone Associates also mentions used capacitve sensors. I found my Baratrons in a couple of junk shops that had dismantled some semiconductor processing equipment.

To those considering using them, the capacitive sensors mentioned above conform to the same overall appearance and put out a 0-10V signal, so they are pretty much interchangable as long as the readout unit can supply enough +/- 15V to run them. This is more of an issue with the temperature controlled units, which take 250-500mA from both supplies. The lower pressure units are all temperature controlled. The 0.1 Torr full scale unit I have is also position sensitive, and must be mounted vertically for optimum results.

Richard Hester

Teflon coated vacuum fittings were the issue - Richard Hull's reply -
>The right angle valve alone makes using the material worthwhile. Just make sure that metal screening covers entrances to this plumbing from the fusor. This should stop the beams and most of the particles which might fry the teflon on that piece. I will be curious how low that stuff can be driven if you plan on going below 10e-6 torr.
>Richard Hull