Re: negative streamer propagation?

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

Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 

Tesla list wrote:
 >
 > Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net>

 > Your observations are consistent with impulse testing of long rod-plane
 > gaps. They also appear to be consistent with initial breakout measurements
 > made by Terry some time back which showed that corona/Trichel pulses
 > develop at lower voltages during negative voltage excursions.

Ok.

 > The reason for the polarity difference for long spark propagation appears
 > to be that, in a non-uniform (divergent) E-field, any free electrons in the
 > gap will be increasing accelerated as they move towards a positive
 > electrode since they are moving into an increasing stronger (converging)
 > E-field. This increases the probability that they'll gain sufficient energy
 > to create secondary electrons as they collide and ionize neutral gas
 > molecules, supporting further avalanche breakdowns and streamer growth. In
 > the case of a negatively polarized electrode, free electrons will be
 > repelled by the diverging E-field into a region with a lower E-field. This
 > tends to reduce the odds that they'll gain sufficient energy to create
 > secondary electrons, and choking off further streamer growth.

Makes sense. Negative corona spreads uniformly over a large ares of the
terminal surface, as if the electrons could not "see" clearly where the
positive terminal is. Positive corona has a plume appearance, with
electron "rivers" feeding larger and brighter channels flowing into
a single point in the terminal.

Antonio Carlos M. de Queiroz