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: Vacuum Lingo, URL
Date: Aug 05, 10:08 am
Poster: Richard Hull

On Aug 05, 10:08 am, Richard Hull wrote:

One of the most difficult areas for the fledgling hands-on fusion aspirant is obtaining a good vacuum system.

The basic understanding of beginning vacuum technology is quite simple. The physical embodiment at the amateur hands-on level is another matter completely. To get a quick intro and learn more, try this URL

This drops you into the wonderful world of the "Belljar" which is a small quarterly publication on amateur vaccum techniques conducted and edited by steve Hansen. It has lots of basic info at the touch of a host of hot buttons. There are numerous links to other related sites as well. It is virtually a must check source for all vacuum neophytes. I have subscribed to the BJ since issue one in the early 90s.

One issue that I will mention is that of units in the vacuum world. Most old hands who work daily in vacuous surroundings all use the Torr as the standard unit. This is most used where the vacuum attained is over a vast range of pressures.

Atmospheric pressure is taken as 760mm of mercury. 1 Torr = 1mm Thus a coarse vacuum might be 50mm or 50 torr. A good roughing pumped vacuum will be in the 50-2 milltorr range, (50 - 2 X10E-3mm).
A deeper vacuum might be 10E-5 torr or so. Good practice would be to use torr, always.

The bulk of rough vacuum work is in the 1 torr to 1 millitorr range. For those of us working solely with roughing pumps, the millitorr which is 1 millionth of a meter of mercury, is shortened to the often used "micron". Thus a 1mm vacuum would be 1000 microns. A good rough vacuum would be 100 microns = 100 millitorr = .1mm. The fusor usually works at a pressure of 10 microns = 10 millitorr = .01mm.

I personally prefer micron for all fusor discussions. The functional pressure range for all fusors are in the 20 to 1 micron range. Micron is just an easier to speak and handy term if one is in the fusor world only. Most good roughing pumps are rated in microns. Most thermocouple gauges read in microns. All good "vacuum heads" are quite comportable with both Torr and microns there being only a power of ten conversion - (decimal place move).

For fusorites this is just another technology to master with a slew of new terms to become familiar with.

Richard Hull