The Positive Streamer Mechanism of Spark Breakdown

The essential conditions for streamer onset in spark breakdown are discussed, with particular reference to the production of photo-ionizing radiation in the initial avalanche. It is shown that the process of electron-ion recombination can adequately account for the production of the necessary radiation, and is probably the predominant process. It is also shown that the yield of photons by this mechanism, and consequently the threshold for streamer advance, is critically dependent upon the space-charge field produced by the initial avalanche While Meek's criterion in its quantitative form gives the order of this critical space-charge field and enables the breakdown voltage for uniform electric fields to be calculated, the newly proposed conditions for photon production give a new physical significance to the criterion.