TSSP: List Archives

From: "Malcolm Watts"
Date: Mon, 13 Nov 2000 08:54:16 +1300
Subject: Re: [TSSP] NSVPI - Latter Results

Hi Barry, all,

On 11 Nov 00, at 12:28, B2 wrote:

> Hi Paul, All,
> 
> > Let me guess that the resistive phase is a short period of constant
> > resistance during which the arc gets established. It looks to be on
> > the order of nanoseconds and is presumably relevant to fast pulse
> > discharges in accelerator and fusion supplies. I take it we can
> > ignore this resistive phase, since tesla gaps conduct for many tens
> > of microseconds?
> 
> > Paul Nicholson,
> > Manchester, UK.
> 
>     There ought to be an initial loss due to channel formation
>     (resistive loss).  Succeeding losses are possibly caused by plasma
>     maintenance, ionizations and reionizations at the voltage
>     reversals, and cathode spot formation and reformation on the
>     opposite electrodes at voltage reversals.  
> 
>     Mitigation of the first loss could be via externally triggering
>     the gap.  The energy loss (resistive phase) is now in the trigger
>     circuit.  Even there, the losses could be minimized with optimized
>     triggering, i.e., fast risetime and multiple streamer formation
>     with concomitant multichanneling leading to lower overall channel
>     resistance and inductance.
> 
>     Mitigation of the remaining two losses could be via a scheme that
>     I am still pondering.  Suppose two spark gaps are constructed. 
>     Suppose each gap is isolated by a high voltage high "pulse"
>     current diode.  This scheme would force the gaps to be
>     unidirectional during the entire conduction period.  Ion and
>     cathode spot leftovers would be preserved (within the normal decay
>     time constants).  Since each gap would be incuring only half of
>     the losses, it would quench faster.  There is the possibility that
>     a trigger circuit could be designed to also aid in gap
>     deionization and quenching.  There is the question as to whether
>     such diodes can be obtained with low enough switching losses.  
> 
>     Anyone think that any part of this would be feasible?

It would be very feasible for small coils using UF recovery diodes 
which can stand repetitive peak currents in the 10's Amps range but 
I'm not familiar with any devices with UF characteristics in the kA 
range. At least the idea is benchtop testable. Snubbing might also be 
usefully investigated at the same time.

Regards,
Malcolm


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.