Random walk of electrons in a gas in the presence of polarized electromagnetic waves: Genesis of a wave induced discharge

Abstract

The average number of collisions N of seed electrons with neutral gas atoms during random walk in escaping from a given volume, in the presence of polarized electromagnetic waves, is found to vary as N=B(Λ/λ)2/[1+C(Λ/λ)]2, indicating a modification to the conventional field free square law N=A(Λ/λ)2, where Λ is the characteristic diffusion length and λ the mean free path. It is found that for the field free case A=1.5 if all the electrons originate at the center and is 1.25 if they are allowed to originate at any random point in the given volume. The B and C coefficients depend on the wave electric field and frequency. Predictions of true discharge initiation time τc can be made from the temporal evolution of seed electrons over a wide range of collision frequencies. For linearly polarized waves of 2.45 GHz and electric field in the range (0.6–1.0)×105 V/m, τc=5.5–1.6 ns for an unmagnetized microwave driven discharge at 1 Torr argon.