TEMPORAL AND CONSTRICTION BEHAVIOR OF LOW-PRESSURE, CATHODE-DOMINATEDARGON DISCHARGES

Measurements of quasi-steady-state voltage-current characteristics, lo w-current voltage and current oscillations, and constriction formation are reported for cathode-dominated discharges in low-pressure Ar. Pul sed a discharges (similar to 5 ms long at 1-3 Hz) reduce heating and i mprove the accuracy of differential voltage measurements. Values of pr essure p times the separation d of the parallel-plane electrodes are 0 .12 to 2 Torr cm corresponding to discharge breakdown voltages of 2 kV to 230 V. Discharge currents range from 2 mu A to 40 mA. The quasi-st eady-state discharge voltages decrease from their breakdown values in direct proportion to the current, i.e., the negative-differential-volt age-to-current ratio is constant. At currents below the onset of self- sustained sustained oscillations and at the higher pressures, the freq uency and damping of transient oscillations are in agreement with a pe rturbation model based on changes in ion-induced electron emission at the cathode caused by space-charge electric fields. At the higher curr ents and low pressures transient voltage and current waveforms show th e growth of low-frequency oscillations accompanying the onset of const rictions. Rotation of the constricted discharge is observed at these p ressures. At the higher pressures the constrictions are stable during the pulse and emission scans parallel to the electrodes provide quanti tative data on constricted discharge areas and emissivity per unit cur rent as the discharge increases in size with increasing current. Compa risons are made of these experiments with recent models where possible .