Neutral particle density modulation in the positive column of a low-pressure mercury discharge modulated at low frequencies

Abstract

A clockwise hysteresis between electron number density and discharge current has been observed in the positive column of a mercury discharge modulated at low frequencies. The hysteresis is shown to be associated with changes in neutral density during the modulation cycle. Rates of neutral density change produced by step transients in discharge current have been measured by monitoring the current required to produce the main Tonks-Dattner resonance of the column. A comparison of these rates with probe measurements of ion wall current indicated that between 2 and 6% of the ion wall flux was retained on the column wall for periods greater than 500 milliseconds. It is shown that this phenomenon satisfactorily accounts for the hysteresis observed when the discharge current is modulated sinusoidally.