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Re: low pressure electrical breakdown



James: This is a common problem for plasma experimentalists who switch
large energy, stored in capacitors, to ionize the contained gas. I'd bet
that they have a number of complete papers on this topic. Of course, the
standard solution is to have a vacuum switch.

I recall that the breakdown voltage of "dry air" is in the CRC Handbook of
Chemistry and Physics, as 8KV/cm. I'd bet that it has listings for
pressures other than STP. Another source that comes to mind is a book
called "Building Scientific Apparatus" (again, this is a recollection of
the title). I'd look there, as it often goes into detail about apparatus
building difficulties.

Finally, one of the demos that used to be done in class is the Crooke's
tube with partial vacuum, in which you have the discharge from one end of
the tube to the next. The Leybold version sat on a ground glass fitting
that allowed you to pump a vacuum, starting at atmosphere, and observe the
"Cathode Rays". The rays were not visible at atmosphere, but as the mean
free path increased, the breakdown of air became visible as a purple stream
between electrodes. Most of these Crooke's tubes produced x-rays, and are
no longer acceptable in the classroom. However, I suspect that the Leybold
instruction sheet on "Cathode Ray Tubes" may have given some data on this
breakdown. Karl

Dear all,

Does anyone happen to know of a reference giving the breakdown field and/or
breakdown voltage of air as a function of pressure, between 1 atm and
vacuum?

I know that there have been messages here before about how the breakdown
goes through a minimum at some pressure well below 1 atm. Searching on the
Web, I can only seem to find information that applies above that minimum.
(i.e., they tell me that the minimum breakown voltage would occur at
perfect vacuum).

Thanks,
--
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry

Dr. Karl I. Trappe Desk Phone: (512) 471-4152
Physics Dept, Mail Stop C-1600 Demo Office: (512) 471-5411
The University of Texas at Austin Home Phone: (512) 264-1616
Austin, Texas 78712-1081