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Re: Book came in

Hi Jim, All,
    It was 19.84 kV per centimeter.  The graph shows 20 kV.  Go figure.
They are
using cable-line generators with an impedance between 50 and 75 ohms.

Barry



Tesla List wrote:

> Original Poster: Jim Lux <jimlux-at-jpl.nasa.gov>
>
> 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