Dynamics of an RF Discharge in a Magnetic Field under Strong Initial Preionization

We demonstrate experimentally the possibility to create and sustain a strongly ionized plasma at low gas pressures by the electromagnetic radiation of the intensity which is below the conventional breakdown level. The conditions of ignition and sustaining the plasma are found, and the plasma parameters are measured. The necessary condition for the discharge formation is strong preliminary ionization of an initial gas. Significant electron heating in the RF field, which ensures the effective gas ionization takes place due to Coulomb collisions with protoplasma ions. Such collisions are much more frequent than the electron-neutral collisions. We propose a qualitative analytical model of the discharge evolution, which describes the effects observed.