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From: abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ))
Newsgroups: net.physics
Subject: Limitations on High Electric Fields
Message-ID: <523@mhuxm.UUCP>
Date: Wed, 19-Feb-86 00:26:06 EST
Article-I.D.: mhuxm.523
Posted: Wed Feb 19 00:26:06 1986
Date-Received: Thu, 20-Feb-86 00:06:22 EST
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 25

Question:

I am aware that the breakdown electric field in air
is typically quoted as 10kV/cm.  In various dielectrics
the breakdown can be higher--400kV/cm in insulating
GaAs is a typical figure for that material.

My question--what is the breakdown field in a vacuum?
What influences it?

In extreme high voltages, pair production may occur.
From a negatively charged electrode, cold emission
can occur sending electrons into the vacuum.  Another
possible effect is due to the lack of a perfect vacuum,
and I recall that in geiger counters a low
pressure is purposely selected to get large currents
because of special properties in the 1 torr or so range.
Do the residual gases always dominate the breakdown process
in practically attainable vacua?  Or possibly can
UHV systems achieve much greater dielectric strengths?

Does anyone have a practical answer to these questions,
or better yet, a good reference?

--Joe Abeles