OSCILLATIONS IN MAGNETICALLY CONFINED COLD-CATHODE DISCHARGES AT VERY LOW PRESSURES

Abstract

Radio-frequency oscillations in a cold-cathode discharge with magnetron geometry have been observed in the pressure range 10−10 to 10−6 Torr. The discharge exhibited two distinct states. In state I, at low magnetic fields, no stable r-f. oscillations were observed and the low-frequency noise was large. In state II, at high magnetic fields, coherent oscillations of very narrow linewidth were observed in the frequency range 15 to 100 Mc/s. The frequency of oscillation was given approximately by f = (nVa)/(πra2B); (Va is the anode voltage, ra the anode radius, and B the magnetic field). Pressure had little effect on f other than a sudden change in mode number (n) from 1 to 2 at higher pressures. It is concluded that a dense rotating electronic space charge exists even at the lowest pressures examined. Calculations of the frequency of oscillation based on this model are in reasonable agreement with the measurements.