Ionization behavior of hairpin argon plasma jets resonantly generated by microwave pulses at atmospheric pressure

Abstract

<p indent="0mm">Atmospheric pressure microwave plasma jet has many advantages, such as high density and high activity. However, their application is limited because it is difficult to modulate the morphology of the plasma jet for specific requirements. This study constructs a pulsed microwave hairpin resonant discharge device to generate an atmospheric pressure pulsed microwave argon plasma jet. The results show that the plasma jet has three typical discharge forms on different pulse frequencies. When the pulse frequency is <sc>10 kHz,</sc> the argon plasma jet changes periodically with an arched plasma morphology at the open end of the hairpin electrode. When the pulse frequency is <sc>30 kHz,</sc> the argon plasma jet presents a nonperiodical change, and the plasma morphology exhibits a crescent-shaped pattern. When the pulse frequency is <sc>60 kHz,</sc> the argon plasma jet presents a largescale nonperiodic change with similar oval plasma morphology. In addition, the spatiotemporal electron evolution process of the argon plasma jet is measured by a microwave Rayleigh scattering device, which reveals that the peak electron density is <sc>4.06×10²¹ m⁻³,</sc> the number of electrons is on the amplitude order of 10¹³, and the number of electrons changes periodically with the pulsed power. Combining the experimental and simulation results, it can be concluded that the formation mechanism of the three discharge forms is attributed to the resonance excitation of the locally enhanced electric field, the ionization wave propulsion in the microwave plasma jet, and the temporal and spatial distribution of different particles in the pulsed microwave argon plasmas.