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Re: Improving spark gaps
It is in one of the pulsed power conference proceedings. Don't recall which
year, but I'll try and find the reference again. I know it was in the same
proceedings as a paper by Miley, et.al. on Inertial Electrostatic
Confinement fusion.
These conferences have tons of papers on spark gaps of various kinds.
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> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Improving spark gaps
> Date: Thursday, June 03, 1999 6:37 PM
>
> Original Poster: "B**2" <bensonbd-at-erols-dot-com>
>
> Hi Jim, All,
> I checked the ieee web site under opera. They don't have anything
> that far back. It would be very interesting indeed to find where you
> found this article. There might be others there also?
>
>
> ----- Original Message -----
> From: Tesla List <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Saturday, May 15, 1999 12:10 AM
> Subject: Improving spark gaps
>
>
> Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>
> A useful article that I ran across recently:
>
> MacGregor, S.J., et.al, "Methods of Improving the Pulse Repetition
> Frequency
> of High Pressure Gas Switches" in an IEEE publication of some kind
> (sadly,
> my computer died, taking my bookmark with it, but I'll try to find it
> again). They are at the Univ. of Strathclyde, so you Glaswegan coilers
> out
> there might want to track these folks down.
>
> They're talking PRFs of 100's to 5 kHz, tens of kV, etc. which is
> right up
> the TC alley. High pressure means 1 bar (1 atmosphere) The paper talks
> about
> the variations in breakdown recovery for both pulsed and DC gaps as
> you
> change pressures and gases. All of this is for static (sealed gaps),
> although they talk about applicability to flowing gas gaps.
>
> Interesting stuff:
> 1) They look at the recovery of a gap in Air and in SF6. There is sort
> of a
> plateau effect. After the gap fires, the breakdown voltage starts to
> come
> back up and is at about 50% after 1 mSec, then holds there until about
> 200-300 mSec, when it comes back to 100%. As you might expect SF6 is a
> bit
> better than air, but not much (5-10%, reading from the graph in the
> paper).
>
> 2) Changing the pressure changes the height of the plateau, but not
> the
> time. At 1.5 bar, the plateau is at 90% of eventual gap strength, but
> still
> takes more than a mSec to get there.
>
> 3) They did some experiments with mixes of He and SF6, because they
> thought
> that high thermal conductivity of the He would help, and apparently
> He/SF6
> blends have been used in flowing gaps. It didn't. It's actually worse
> in the
> static gap.
>
> The most important thing they found is that putting a field on the
> gap
> after discharge helps to "sweep" the ions out (as would fast (i.e.
> supersonic) gas flow, like in a Fruengel argon gap). Then, they go
> through
> and talk about how you can stabilize a gap, increasing its recovery
> rate by
> adding corona in a SF6 gap. The corona "inhibits the breakdown in the
> gap
> until the voltage reaches the required value". They have a histogram
> of gap
> breakdown times where the corona stabilized version is tightly packed
> around
> 1 mSec and the unstabilized one is all over from 0 to 2 mSec, with a
> big
> hump at <100 uSec. They used a rod/plane gap, which has a lot of
> corona, as
> opposed to a uniform field gap. Their gap was 20 mm and the rod was 2
> mm in
> diameter in SF6 at 0.5 bar. Finally, they show a graph of a relaxation
> oscillation where the period is 200 uSec (5 kHz) and the voltage on
> the gap
> is 36kV. I assume from the waveform shown that it is a resonant
> charging of
> a capacitor (at least that's what the shape of the rise looks like).
>
>
>
>
>
>
>