Beam-plasma interactions in a hollow cathode

A new hollow-cathode effect has been observed in the residual plasma of a mercury arc discharge. A pair of negatively biased plane parallel electrodes were found to give rise to an orderly sequence of high frequency electrical bursts. The bursts made negligible contribution to ionization in the plasma. Similar bursts were subsequently observed in a self-sustained hollow-cathode discharge. The timing of the bursts and their variation with pressure in the range 2 to 15 mTorr are in good agreement with a simple theory based on multiple-mode resonant interaction of secondary electrons with a decaying plasma. In the present tube, the frequencies of the oscillation within each burst are predicted to lie between 100 MHz and 20 GHz.