Effect of Different Discharge Modes of Hollow Cathode Discharge on Electromagnetic Wave Propagation

This paper studies the discharge characteristics of helium hollow cathode discharge plasma and its effect on microwave transmission. The voltage-current (V -I) characteristics and Paschen curve were measured during the experiment. It is found that there are two types of discharge in this hollow cathode discharge. When the supply voltage is lower, the plasma is a "conventional" discharge and exhibits abnormal glow discharge (AGD) properties which are characterized by low current and high voltage. This is a discharge in a hollow cathode (D-HC). When the supply voltage is gradually increased, the discharge reaches a hollow cathode discharge (HCD), the voltage is drastically reduced, and the current is several dozens of times the value of the D-HC, and the slope of the V -I curve is significantly reduced, which marks that the hollow cathode effect (HCE) is reached. To further investigate the internal discharge principle of hollow cathode and the effect on electromagnetic wave propagation, the electron energy distribution function (EEDF) of the plasma in the hollow cathode discharge is diagnosed based on the Langmuir probe theory, and the energy distributions of the main body electrons and some of the fast electrons are analyzed under different discharge modes. The results show that with the increase of the current and the emergence of the HCE, the peak of the main slow electron EEDF changes from gradually increasing to gradually decreasing, the pendulum effect starts to appear, the number of main electrons gradually decreases, while the hollow cathode effect becomes more obvious. It is observed that at higher currents, the EEDF also shows high-energy helium peaks as well as peaks for cathode sputtering material. And then, the effect of hollow cathode discharge plasma on electromagnetic wave transmission is investigated using numerical simulation methods.