Two-dimensional numerical simulation of pre-ionizeddirect-current glow discharge in atmospheric helium

In this paper, the effect of pre-ionization on the small-gap and large-gap direct-current glow discharge atatmospheric pressure are investigated based on a two-dimensional self-consistent fluid model. For both thedischarges, the results show that with the enhancement of pre-ionization, the charged particle distributiongradually shifts toward the cathode along the discharge direction, making the cathode fall zone shrinkcontinuously. The width of the positive column region, negative glow space, and cathode fall zone continuouslyextend along the vertical discharge direction, and the distribution of electron density and ion density are moreuniform. For the electric field, with the enhancement of pre-ionization, the longitudinalal componentdistribution of the electric field in the cathode fall zone gradually contracts toward the cathode, and the overallelectric field near the cathode decreases and becomes more uniformly distributed. The transverse componentdistribution of the electric field gradually decreases and shrinks toward the wall. The overall electrontemperature in the discharge space decreases with the enhancement of the pre-ionization level, and the electrontemperature distribution in the cathode fall zone gradually shrinks toward the cathode. In addition, the overallpotential of the discharge space also decreases. The introduction of pre-ionization significantly reduces themaintaining voltage and discharge power of the direct-current glow discharge. Furthermore, the potential dropin the small-gap discharge is always concentrated in the cathode fall zone as the pre-ionization increases, whilethe potential drop in the large-gap discharge is gradually shifted from the cathode fall zone to the positivecolumn region. This simulation shows that the pre-ionization not only effectively enhances the dischargeuniformity, but also largely reduces the maintaining voltage and energy consumption of the direct-current glowdischarge. This work is an important guideline for further optimizing the electrode configuration and theoperating parameters of the plasma source