OSCILLATIONS OF LOW-CURRENT ELECTRICAL DISCHARGES BETWEEN PARALLEL-PLANE ELECTRODES .2. PULSED DISCHARGES IN H-2

Measurements are made of damped oscillations in the current and voltage induced by a voltage pulse applied to the stabilizing resistor of discharges in H-2 at pressure times electrode spacing values of 0.3 to 1 Torr cm (40-133 Pa cm) operating at voltages of 300 to 2100 V. The use of pulses less-than-or-equal-to 1 ms long and repetition rates of 10 Hz results in low ion bombardment of the cathode. For pulse currents of 0.01 to 5 mA (2 X 10(-7)-10(-4) A/cm2) and an electrode separation and area of 1 cm and 50 cm2, the frequencies and damping constants are 10-300 kHz and 2 X 10(3)-10(5) s-1, respectively. The current densities are small enough so that space-charge distortion of the electric field is small, but not negligible. At currents below those for oscillation growth, the steady-state discharge voltage decreases as expected for a constant negative differential resistance. Values of 1000 to 4000 OMEGA are obtained depending on pressure and cathode condition. Transient models, developed in an accompanying paper, relate the frequencies, damping constants, and onset of oscillation growth to ion transit times, electron ionization coefficients, and ion-induced electron yields. The growth of discharge current immediately after the application of the voltage pulse is also used to determine discharge parameters.