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RE: VACUUM TECHNOLOGY


 > From: "SROYS"  <SROYS-at-radiology.ab.umd.edu>
 > Date:         Fri, 10 Feb 1995 09:34:01 EDT
 > Subject:      Re: Vacuum technology

 SR> I have heard the term vacuum quench gap, but what exactly would a 
 SR> vacuum quench gap do that an air-blast gap wouldn't and what are 
 SR> some construction details?  I have an old Sargent-Welch vacuum pump 
 SR> (like you would find in a high school), and I was wondering if that
 SR> would  give a hard enough vacuum or would I need some sophisticated
 SR> (i.e. -  expensive) vacuum system.
 SR> Steven Roys (sroys-at-radiology.ab.umd.edu)

"Vacuum Gaps" make it sound like some difficult technology. This one
was pioneered by Richard Hull: it is simply a series static spark gap
that is quenched with air moving from normal pressure into a low 
pressure box or chamber. The air is kept at low pressure in the box
or chamber by mounting a vaccum cleaner motor.

I have a pretty nice vacuum gap that is quenched with a series wound
240 volt commercial shop vac powerhead. The vacuum motor assembly is
mounted in a tightly constructed wooden box. One section, side, or 
hole is left open in the box construction where sections of hard 
copper water pipe are mounted in a row. This row of pipe sections
with tiny gaps between them forms the series of static electrodes. 
When the vacuum motor is turned on, the air pressure in the box is 
lowered, and the only inlet is the narrow spark gaps formed between 
the copper electrodes. Air moving into the low pressure box speeds 
up rapidly as it is forced into the narrow spaces between the elec-
trodes. The rapidly moving air removes heat directly from the elec-
trode face, and it also acts to physically stretch and cut the arc.

The series wound motor I am using can have the RPM adjusted by using
a variac to control the input voltage; this in turn varies the 
pressure, and therefore the quenching action, of the gap. These gaps 
are a bit tricky to build and de-bug, but they are efficient, quiet, 
and will quench well at high power. The electrodes are cheap, and
easily replaced when they wear out.

Richard Quick

... If all else fails... Throw another megavolt across it!
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