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Re: Pseudospark
Tesla List wrote:
>
> Original Poster: "L. Robertson" <LWRobertson-at-email.msn-dot-com>
>
> Hi ...
>
> I notice in the IEEE pulsed power conferences
> numerous mentions of "pseudo-spark" gaps. Does
> anyone (Richard) have a clear idea of what exactly
> these are? They seem to be used as power switches,
> but some of the descriptions seem to indicate they
> are also used as radiation sources, or am I missing
> something.
>
> Seems to me the DND efforts to supply power to
> rail launchers and other power intensive things
> might on a smaller scale be applicable to our
> efforts.
>
> LR
Larry,
The confusion comes about because this device was first introduced as an
electron beam source when it was initially developed (~1980). During the
time it switches from non-conducting to to an ultra-dense glow, it can
generate a powerful (but brief ~10 nS) high-current electron beam. It's
use in high power switching applications was delayed because it was
thought that its turn-on rate (dI/dt) was too slow compared to existing
high power thyratrons or sparkgaps. A fair amount of research is
continuing in this arena by high power pulse researchers in fusion,
nuclear, and high-power laser research.
A psuedospark switch is a low pressure gas discharge switch. Pressure is
set such that the electron mean-free path is approximately equal to the
electrode gap spacing. Relatively large hollow electrodes are used,
similar to a thyratron's structure. In operation, a hollow cathode
discharge is transformed into a super dense glow discharge, located at,
and around, the edge of the cathode hole. By careful control of
geometries and matching to the external pulse forming network, dI/dt
rates approaching 10^12 A/Sec can be achieved. Triggering may be done by
injecting electrons in/near the cathode hole via a high voltage pulse,
UV laser pulse, or via a sliding spark (sort of like a cross between a
triggering grid of a thyratron and the trigger electrode in a
trigatron).
The downside: since these devices operate at reduced pressures, and are
not (AFAIK) commercially available, a degree of expertise and
theoretical knowledge would be required to design and construct one of
these and make it work properly. They may have the potential to replace
high power hydrogen thyratrons in the future.
-- Bert --
Reference: Gerhard Schaefer, in "Gas Discharge Closing Switches
(Advances in Pulsed Power Technology, V2)", Plenum, 1991