Study on the periodic discharge characteristics of atmospheric-pressure dual-pulse-modulated microwave Ar plasma jet

Atmospheric pressure microwave argon plasma jet, due to its high electron density and abundant active particles, holds significant application prospects in fields such as material modification and biomedicine. However, the irregular fluctuations in their spatiotemporal distribution limit precise control and hinder practical applications. To address this, this paper employs a dual-pulse modulation approach to investigate the periodic evolution characteristics of the microwave plasma jet and the influence of the duty cycle of the high-frequency pulse on the periodic evolution characteristics of the argon plasma jet. The experiments reveal the following findings: (1) When maintaining a high-frequency pulse 50% duty cycle, as the number of pulse cycles increases, the plasma jet gradually transitions from an unstable transient discharge to a stable discharge, ultimately forming a stable plasma jet. The mechanism underlying this evolution process can be explained as follows: In the initial discharge, the lack of residual electrons leads to transient random discharge fluctuations. In subsequent cycles, residual seed electrons and active particles continuously accumulate, promoting the stability of the discharge process. Eventually, the residual electrons and active particles further accumulate to saturation, driving the ionization wave to form a stable plasma jet and maintaining a stable discharge morphology. (2) Increasing the duty cycle of high-frequency pulse advances the timing of initial discharge, stable discharge, and the formation and maintenance of a stable plasma jet. This is because longer pulse duration prolongs the accumulation time of seed electrons and active particles, while shorter pulse interval reduces the decay time of seed electrons and active particles, accelerating the accumulation of charges and excited state particles. Furthermore, a higher duty cycle of high-frequency pulse promotes the broadening of the secondary ionization peak and extends the duration of secondary ionization enhancement, enabling faster establishment and maintenance of the discharge channel. The research results reveal the periodic discharge regularity of the dual-pulse-modulated microwave Ar plasma jet, providing an important reference for the precise control of the stability and spatiotemporal distribution of parameters of the atmospheric pressure microwave plasma jet.