Re: Book came in

To: tesla-at-pupman-dot-com
Subject: Re: Book came in
From: Jim Lux <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Mon, 19 Oct 1998 17:30:20 -0600
Approved: terryf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: "B**2" <bensonbd-at-erols-dot-com>
> 
> Hi All,
>     The book Physics of Pulsed breakdown in Gases by Korolev and Mesyats
> came in the mail, finally.  A quick overview indicates that most of the
> cases are for around atmospheric pressure discharges.  On page 123 there is
> a calculation of when the voltage across a volume discharge, of 1 cubic
> centimeter and 1 centimeter in length, starts to drop.  They calculate 1
> kOhm.  Interesting number?  On page 73 is a graph of the result of a
> simulation verified by experiments.  The graph is for a current limited
> voltage source of 20 kV across a 2 centimeter gap in 500 torr nitrogen.
> The current limiting resistance  was 485 ohms and the interelectrode
> capacitance was 28 pF.     The graph indicates that the current in the gap
> didn't reach 1 Ampere until a time of 30 us had passed.  This was when the
> voltage across the gap started to fall!
> 
> Barry

20 kV across 2 cm is only 10 kV/cm, which is less than a third of the
breakdown for atmospheric air, which is mostly nitrogen. Sure, the
pressure is less, by 500/760, which would be expected to reduce the
breakdown voltage by a comparable amount, but still the breakdown
voltage is way higher than 20 kV (I guesstimate about 40 kV).  

It is well known that the higher the overvoltage the faster the gap
breaks down, so with a massive undervoltage, one could expect the
breakdown to develop very slowly.

I assume the source was DC? Was it a uniform gap, sphere gap, or what?

That the voltage started to drop when the current reached 1 Amp isn't
surprising, as that is when the resistance of the gap starts to really
decrease, increasing the voltage drop across your current limiting
resistor.

-- 
Jim Lux                               Jet Propulsion Laboratory
ofc: 818/354-2075                     Mail Stop 161-213
lab: 818/354-2954                     4800 Oak Grove Drive
fax: 818/393-6875                     Pasadena CA 91109