高气压直流辉光CH4/H2等离子体放电过程中的占空比效应

Effect of Duty Ratio on High Pressure DC Glow Discharge of CH4/H2 Plasma

对高气压下直流均匀辉光放电的脉冲占空比效应进行了研究。在1.7 kHz脉冲放电条件下,当占空比高于73%时,脉冲间隔后电压需要经过10~20μs的上升时间至稳定;而电流增长明显地滞后于电压的上升,整个增长过程需要的时间约是电压上升时间的10倍。减小占空比,表示电流增长快慢程度的时间常数τ几乎线性增加。这是因为小占空比时,上升通道开始时刻的等离子体电子密度低,放电电流需要更长时间才能稳定。在高气压条件下,粒子碰撞效应显著增强,增加的放电功率被更多地被用于加热中性粒子,表现为Hα、Hβ等发射光谱强度随占空比降低而增加。进一步减小占空比,电子密度n_e衰减到过低,时间常数τ增加到一定值时,放电就难以维持,表现为放电不稳定乃至熄灭。

The effect of duty-ratio on the characteristics of high pressure DC glow discharge of CH4/H2 plasma was investigated by monitoring the current/voltage waveforms and diagnosis of plasma emission spectrum.The results show that the duty-ratio has a major impact.For instance,with a duty-ratio above 73% at 1.7 kHz,it took 10~20 ms(100~200 ms) of rising time for the voltage(current) to be stable.The current increased with the increasing discharge voltage in a rapid-slow manner,considerably lagging behind the voltage.As the duty-ratio decreased,the time constant increased almost linearly,because smaller duty-ratio produced lower electron density at the beginning of ascending channel.At a high pressure,as the duty-ratio decreased,the Hα and Hβ emission intensities increased because the increased discharge power heated neutral particles,significantly promoting particle collision.A duty-ratio too small reduced the e-density and increased the time constant,resulting in an unstable or quenched discharge.