OSCILLATIONS OF LOW-CURRENT ELECTRICAL DISCHARGES BETWEEN PARALLEL-PLANE ELECTRODES .1. DC DISCHARGES

The oscillatory behavior of dc discharges between parallel-plane elect rodes (1 cm spacing) at low pressures (0.5-3 Torr) is measured and com pared with models. For hydrogen these discharges are unstable for wide ranges of discharge current below 0.2 mA/cm2 and external circuit res istances above almost-equal-to 4000 OMEGA. Lateral constrictions of th e discharge occur over a much more limited range of currents and press ures than do oscillations. Laser-induced photoelectron pulses produce damped oscillations for discharge currents below those at which self-s ustained oscillations are observed. The frequency of the oscillations varies approximately as the square root of the discharge current and t he damping of the oscillations increases with the discharge current. T hese results agree with simple models developed in an accompanying pap er [this issue, Phelps, Petrovic, and Jelenkovic, Phys. Rev. E 47, 282 5 (1993)]. Some data are presented for argon and nitrogen.