Temporal evolution of harmonic characteristics in atmospheric pressure pulsed RF discharges

Evolution of current harmonics excited by the third harmonic series resonance between the external circuit and plasma under varying discharge conditions was experimentally investigated in atmospheric pressure pulsed radio frequency (RF) discharges. Fast Fourier Transform analysis of voltage and current waveforms revealed the following: (1) At a fixed pulse repetition frequency, reducing the duty cycle caused the quasi-steady-state third harmonic resonance point at the tail of the pulse plateau to shift toward the high-power region; (2) under fixed pulse parameters, when the RF power at the trailing edge of the pulse plateau exceeds the resonance threshold, the transient harmonic resonance point during the plateau phase exhibits a progressive shift from the trailing edge toward the leading edge with increasing power; (3) during the pulse rising edge phase, the amplitude and position of the harmonics exhibited complex changes based on the pulse-off time. These results indicate that these changes in resonance points are attributed to the ability of the discharge capacitor to achieve the values required for harmonic series resonance under various operating parameters.