The Decay and Recovery of the Pulsed Emission of Oxide-Coated Cathodes

Abstract

The decay and recovery of the pulsed emission of cathodes consisting of BaO on nickel are studied. The emission of the cathodes is measured in diodes of cylindrical geometry having water-cooled copper anodes spaced 0.019 inch from the cathode. Most of the diodes show a decay of anode current when first put in pulse operation. Decays of 2–50 percent are observed during 150-μs pulses. The decay tends to disappear when the tubes are aged under pulse conditions. The peak current is a linearly decreasing function of the logarithm of the duty cycle, even when there is no perceptible decay during the pulses. The rate of decrease is independent of the pulse repetition rate and decreases with cathode temperature. Current-voltage characteristics during the pulse and recovery periods are obtained by short sampling pulses. A comparison of these characteristics with computed ideal characteristics does not discriminate unambiguously between a variation of emission and a variation of internal cathode impedance as a source of current decay. Studies to separate the contributions of these effects are in progress.

Oxide Coated Cathode Plasma Source of Linear Magnetized Plasma Device

“…The natural logarithm of the cathode emission current is proportional to the square root of the discharge voltage ( Fig. 7(c)) [3,9,18,19] . Fig.7 Cathode emission current densities as a function of cathode temperature (a) and discharge voltage (b) for argon plasma.…”

“…Though we can operate the coating source with the maximum discharge current density as large as 9 A/cm 2 to 10 A/cm 2 , a 1-5 mm diameter coating will usually be blown off the cathode in this extreme working condition. This phenomenon is called sparking [9,14,18,19] . The discharge current increases to an abnormal value sharply during a sparking event.…”

“…The natural logarithm of the cathode emission current is proportional to the square root of the discharge voltage (Fig. 7(c)) [3,9,18,19] .…”