大气压脉冲调制微波发卡氩等离子体射流的电离行为研究

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

大气压微波等离子体射流具有高密度、高活性的优点,但是难以调制出特定需求的等离子体射流形貌,从而限制了微波等离子体射流的应用范围.本文构建了脉冲微波发卡谐振放电装置,产生了大气压脉冲调制微波氩等离子体射流.实验表明,脉冲调制微波等离子体射流存在三种典型的放电形态:当脉冲频率为10 kHz时,氩等离子体射流呈现周期性变化,且在发卡的开口端形成了拱形的等离子体形貌;当脉冲频率为30 kHz时,氩等离子体射流呈现非周期性变化,等离子体形貌为月牙形;当脉冲频率为60 kHz时,氩等离子体射流呈现大尺度非周期性变化,此时形成了类椭圆形等离子体形貌.此外,微波瑞利散射实验测定了氩等离子体射流的时空电子演化过程,得出电子密度峰值为4.06×10^(21) m^(−3),电子数在10^(13)的量级且随入射功率呈周期性变化.结合实验和仿真结果,三种放电形态的形成机制可归因于局域增强电场的共振激发、微波等离子体射流中的电离波推进、脉冲调制微波氩等离子体中不同粒子的时空分布等共同作用.

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 10 kHz,the argon plasma jet changes periodically with an arched plasma morphology at the open end of the hairpin electrode.When the pulse frequency is 30 k Hz,the argon plasma jet presents a nonperiodical change,and the plasma morphology exhibits a crescent-shaped pattern.When the pulse frequency is 60 kHz,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 4.06×10^(21) m^(−3),the number of electrons is on the amplitude order of 10^(13),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.