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.

Radar cross-section reduction by tunable low-pressure gas discharge plasma

“…The experimental results were obtained as outlined by the following procedures. First, we measure the plasma electron density and electronneutral collision frequency of the plasma tubes and describe their temporal and axial inhomogeneity based on our previous work [20]. Then, in the second and fourth parts of this section, we discuss the set of tests and analysis of normal and oblique incidence, respectively, on TE and TM polarization.…”

“…Moreover, the mercury vapour pressure was controlled with a wall temperature from room temperature to 40 • C corresponding to a vapour pressure of 2-6 mTorr. By adding an appropriate amount of mercury vapour to argon gas, the temporal instability could be minimized [20].…”

“…First, we applied a 5 kV AC high voltage to ignite the plasma tube, then 1.5 amp AC with 100-200 volts was injected into the plasma in the glow discharge condition. The operating frequency of the power supply was set at 18 kHz to achieve uniform longitudinal and temporal plasma [20].…”

“…We used an anechoic chamber with flat absorbers (−30 dB in 12 GHz) to isolate the transmitted signal from reflections and multipath or resonance interference. Further measurement details are given in our previous work [20]. Figure 4 shows the schematic illustration of the experimental setup.…”

Investigation into wideband electromagnetic stealth device based on plasma array and radar-absorbing materials

“…Radar stealth technology has always been a research hotspot in the field of anti-detection. The key to radar stealth is primarily to reduce the target's radar cross-section (RCS) to a level that is undetectable by the radar [1,2]. Generally, the RCS reduction methods rely on modifying the target's geometry and loading the target with the radar-absorbing material (RAM) [3].…”