Re: Magnetizing current in SSTCs, my previous posting

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I wouldn't argue about the femto-seconds but I
>wonder about the ratio of electric energy that gets put into
>disassociating the electrons vs. the energy that goes into heating up the
>air.  Would not that ratio be quite large?  In other words, would not the
>air have to become substantially heated up before the coil-system's
>energy becomes substantially dissipated into the seen-and-heard spark?

I'd argue with femtoseconds... Most breakdown theories have the air getting 
ionized by collisions with fast moving electrons from other previously 
ionized atoms (the so-called avalanche theory). Time scale would be on 
order of nanoseconds (depending on field, gap length, and gas density, 
tying in with mean-free-path of the electrons).

There IS field emission (i.e. the field itself causing the electron to be 
stripped), but it takes real high fields.  Most breakdown theories assume 
that the "first" electron comes from "somewhere else" (photoelectric 
emission, stray cosmic ray, etc.), and that as long as the "first" electron 
collides sufficiently hard with something else before it recombines 
(microseconds time scale), the avalanche can get going.

The question raised above is whether there is significant thermal 
ionization or if the ionization would be mostly from the E-field.  The 
usual theory on breakdown has the leader process (which is quite fast) 
making the initial "connection" across the gap by means of successive 
avalanche, and then, once the path is established, ohmic heating gets the 
rest of the column hot, where thermal ionization can be dominant.