基于场致二次谐波的大气压脉冲流注放电时变非均匀电场测量研究

Time-varying Non-uniform Electric Field Measurement of Atmospheric-pressure Pulsed Streamer Discharge Based on Electric Field Induced Secondary Harmonic

诊断大气压脉冲流注放电空间电场是实现流注放电精准调控和揭示等离子体不稳定性机制的重要基础。基于场致二次谐波的空间电场测量方法具有非侵入式、时空分辨率高等优点。然而,流注放电时变非均匀电场对二次谐波信号产生过程的影响规律尚不完善,真实电场标定系数随流注放电不同阶段的变化规律尚不清晰。该文首先计算二次谐波信号产生规律和电场空间分布的影响;然后,基于等离子体流体模拟,分析二次谐波信号对流注放电不同阶段时变非均匀电场的敏感程度;最后,基于纳秒脉冲激光场致二次谐波电场测量平台,实验获得了重频脉冲作用下组合电极结构产生的单根负流注轴向电场演变规律,分析脉冲重复频率对空间电场的影响机制,并针对流注放电时变非均匀电场特点提出电场致二次谐波测量优化若干建议。

Spatial electric field diagnostics of atmosphericpressure pulsed streamer discharges are crucial for accurately modulating streamer discharge characteristics and unveiling plasma instability mechanisms.The electric field induced secondary harmonic method has advantages of nonintrusiveness and high spatial-temporal resolution.However,effects of time-varying non-uniform electric field on the secondary harmonic generation are unclear.Meanwhile,the actual electric field calibration factor may be dependent on the streamer discharge stages.Secondary harmonic signal generation and effects of the external electric field profile are analyzed.Sensitivities of the secondary harmonic signal on the time-varying non-uniform electric fields of different streamer discharge stages are analyzed based on the plasma fluid modelling.Furthermore,based on the nanosecond pulsed laser secondary harmonic generation measurement platform,spatial axial electric field evolutions of single repetitively pulsed negative streamer are experimentally obtained in a combined electrode structure.Effects of the pulse repetition frequency on the spatial electric field are unveiled.Several suggestions of improving E-FISH measurement are proposed based on timevarying non-uniform electric fields of streamer discharges.