Formative processes of cold-cathode Penning discharges at low pressures

Abstract

Formative times td, the time intervals between application of stepped discharge voltages and appearance of discharge currents, for cold-cathode Penning discharges were investigated to reveal their formative processes. Experimentally, a spontaneous discharge initiation belongs to either of two distinct patterns, in that td values (1) scatter over a broad time range and are distributed exponentially, or (2) concentrate in a short time range where the difference between the maximum and the minimum is far smaller than the mean. Low discharge voltages result in initiation in pattern (1), while high voltages result in initiation in (2). Magnetic field and pressure do not explicitly affect an initiation-pattern decision. A thin pin fixed on a cathode plate is effective in causing initiation in pattern (2). The discharge was revealed to be triggered by an electron extracted from the cathode by a strong electric field. Two models for the formative processes were presented. Every electron extracted from the cathode is assumed to be, in one model, reabsorbed by the cathode after a flight unless it collides with gas molecules, or in the other model, captured in the Penning trap. Discharge-formative properties were formulated from those models. They include discharge-current waveforms, dependence on discharge conditions of means, dispersion-to-mean ratios, and distribution patterns of td values. The experimental results agree quantitatively with theoretical results derived from either of the two models. This agreement shows that both the models are valid. For an actual discharge, in which model its formation proceeds is decided by the condition for the discharge.