Radio Frequency Breakdown in Penning Geometries with Nonlinear Fields

Radio frequency breakdown in air (10−3 to 10−6 Torr) is studied analytically and experimentally for two electrode configurations which lead to nonlinear Mathieu-like differential equations for the confined electron motion. Experimental data are identified with two energy-gain mechanisms which are described as the collisional and resonance modes. Breakdown voltages are predicted from stability plots which show several resonance minima where the observed rf breakdown voltages are very low. Resonance minima predicted by a linear analysis are shifted by nonlinear effects, from which it is shown that the collisional mode is apparently triggered by excitation of the 7.7-eV level of the nitrogen molecule with subsequent electron emission from the cathode surface. The resonance mode is found to be largely surface independent.