Influence of secondary-electron emission from MgO surfaces on voltage-breakdown curves in Penning mixtures for insulated-electrode discharges

Voltage-breakdown curves in a Ne+0.1% Ar Penning mixture for insulated-electrode discharges are strongly influenced by changes in the surface properties of a deposited MgO cathode. A model has been developed to calculate an effective secondary-electron-emission coefficient γ in Penning mixtures as a function of the insulator-energy-band parameters. Incorporation of the calculated γ into the breakdown criterion results in good agreement between calculated and measured voltage-breakdown curves for differently prepared MgO cathode surfaces. The calculated results show that the value of γ for argon ions depends on the state of the MgO surface, and this occurs through a change in the width of the band gap of MgO. The results also show that a nonzero value of γ (Ar+) significantly lowers the breakdown voltages and changes the shape of the breakdown curves at higher values of P0d.