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: Questions answered
Date: Dec 24, 9:19 pm
Poster: Tom Ligon

On Dec 24, 9:19 pm, Tom Ligon wrote:

>For those experienced in micron vacuums, you will be in for a surprise as you drift into the higher vacuum regions. Cleanliness is everything. Bakeouts can become a must. Once 10e-6 torr is achieved, you will rather take a severe beating before you will want to take the system back up to air to change internals in the fusor.

We recently obtained a fairly good-sized chamber, 4 ft diameter and about 6 ft long, surplus, for $1000. We knew its history and were not expecting much. It is an old steel pressure vessel adapted for vacuum, with a cruddy interior finish. Its old owners never saw it go below 1e-6 torr.

We hung a 1100 L/sec turbopump on it, and, after getting the obvious leaks sealed up, switched on the turbo. The tank would not pull below 2e-3 at first. When it scootched down below 1e-3 we switched on the RGA to see if the problem was a leak. Nope, just water vapor. Given a few days we got it into the high -7's.

Another chamber, much larger, made of electropolished 316 stainless, pulled down promptly to the low -7's.

That book referenced here recently has instructions for electropolishing. The citric acid needed is available as a cleaning supply from McMaster-Carr.

The company that built that chamber tells us a UV lamp is available that breaks down water vapor, and can reduce the need to bake out in the high vacuum range. I would expect a Fusor would have this effect automatically, as it should produce pretty intense vacuum UV.