Viton is OK, but for a major edge sealing (chamber halves) the large conflat fittings are better, especially with all the electron beams zipping around the inside of the chamber. The copper rings aren't all that expensive and can be reused as many as three or four times.
I do use the viton KF seals for the vacuum lines and such, where the E beams can't bombard the viton. They also don't get quite as hot as the chamber shell during short fusor runs either.
I would personally prefer all conflat fittings, but must tradeoff against expense and ease of disconnect for most all vacuum applications.
Richard Hull
Created on Wednesday, March 07, 2001 12:22 PM EDT by Richard Hull