Nonlinear effects in the positive column of a strongly modulated mercury-rare gas discharge

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Abstract
The properties of the positive column of strongly modulated low-pressure gas discharges in mercury-rare gas mixtures have been studied, both experimentally and theoretically. The current was modulated sinusoidally with a modulation depth of 50%. Calculations have shown that in a limited frequency range nonlinearities in the system have an effect on the time-averaged electron temperature, electron density and excited atom density, and on their waveforms. This behaviour was confirmed by experiments, in which the electron temperature and density were measured by means of microwave techniques and the excited Hg atom densities by measuring the optical absorption and emission. For higher modulation depths differences occur between the results of the calculations and experiments. These discrepancies were found to be more pronounced in pulsed discharges, and are ascribed to changes in the high-energy tail of the electron velocity distribution function.