The influence of electrical waveform on the electron density and collision frequency of low-pressure gas discharge plasma

Abstract

In this experimental research, the effect of electrical waveforms including direct current (DC), sinusoidal, sawtooth, triangular, modified sinusoidal and square wave on the plasma electron density and collision frequency of the positive column of low-pressure gas discharge (PAr = 10 Torr, PHg = 6 × 10−3 Torr, R = 18 mm, Irms = 400 mA) was examined. Time-resolved plasma electron density and collision frequency were measured by fast time-resolved microwave interferometry with simultaneous current and voltage measurements. In the case of direct current excitation, the striation with 800 Hz fluctuation was observed. In a sine wave, the striation was observed at 50 Hz while it was disappeared at 5 kHz. In the square waveform, the collision frequency that keeps the plasma density constant could be controlled by tuning the excitation frequency. It was also found that a rapid change in the electrical current signal, like the sawtooth waveform, causes a total reduction in the electron density and collision frequency. Studying the rectangular pulse periods, showed that the maximum density and collision frequency, as well as their evolutions, could be controlled. Regarding the obtained results, it was concluded that one could effectively control (increase or reduce) the electron density and collision frequency with respect to the critical time intervals for practical applications such as plasma antennas and plasma RCS reduction.