Experiment and simulation on the micro-hollow cathode sustained discharge in helium with different geometries of the second anode

Abstract

The micro-discharge with a hollow cathode and a second anode with different geometries is experimentally and numerically studied. Effects of the second anode on the micro-hollow cathode sustained discharge (MCSD) in helium are investigated. Three kinds of electrodes with different geometries are used as the second anode. The results show that when needles are inserted into the plate to be used as the second anode, the formation of MCSD can be promoted, and MCSD can be obtained at a low cathode current. Moreover, the distribution of needles has an important influence on the formation of MCSD. The cathode breakdown threshold currents for the three cases of the second anode from low to high are as follows: 13 needle-plate, five needle-plate, and plate with no needles. At the same cathode current, a stronger MCSD and a higher second anode current can be obtained when needles are inserted into the second anode plate compared with that when only a plate is used as the second anode. In the present experiment, the volume of MCSD reaches approximately 10 cm3 with an electron density of 4–5 × 1017 m−3 and an electron temperature of 2–3 eV. The experimental and simulated results show that the MCSD originates from cooperative formation between the micro-hollow cathode discharge in the cavity and the discharge around the second anode. Compared with that when only a plate is used as the second anode, when needles are inserted into the second anode, the electric field, electron temperature, and electron production rates near the second anode increase, and a stronger discharge is generated near the second anode. When the needle-plate is used as the second anode, the electron density in both the axial and radial directions in the MCSD region is higher than that when the plate without needles is used as the second anode. Before the formation of MCSD, the electrons generated by the strong discharge near the second anode extend toward the first anode, thus promoting the formation of MCSD.

Absolute atomic nitrogen density spatial mapping in three MHCD configurations

“…The MCSD breakdown voltage is much lower in our case, likely because the pressure differential may extract charged particles from the MHCD electric field and pre-ionizes the gap between the MHCD and the substrate. In 2023, He et al [31] reported a similar regime in experiment using a third electrode covered with several needles. A relatively low voltage applied on the third electrode (200 V) is necessary to induce the breakdown.…”

Numerical simulation and experimental diagnostics of fast electron kinetics and plasma parameters in a microhollow cathode discharges in helium

“…However, it should be noted that fluid models [25][26][27][28][32][33][34][35] do not take into account nonlocal ionization by fast electrons in negative glow plasma in short glow discharges and discharges with a microhollow cathode. The main consequence of the nonlocality of the ionization source in the negative glow region is that the electric field strength in this region takes values close to zero, and the temperature of the main group of electrons is low and amounts to tenths of 1 eV [36][37][38][39].…”

“…Note that in recent years, hybrid models of gas-discharge plasma have gained great popularity, in which heavy particles (ions, excited particles, neutrals) are described by the fluid approximation equations, and electrons by the PIC/MCC method [34][35][36][37][44][45][46][47][48][49][50][51][52][53]. The idea of this method is as follows: the trajectory of an electron starting from the cathode is calculated according to the equations of motion mechanics in a given electric field; in this case, the elastic and inelastic scattering of an electron is taken into account as a random process.…”

“…As a result of such numerical solutions, the empirical distribution of the ionization source is determined and the system of fluid equations for electrons and ions is closed. Despite the success of numerical calculations [34][35][36][37][44][45][46][47][48][49][50][51][52][53], such models are often limited by computational resources and do not allow taking into account the completeness of the processes occurring in a nonequilibrium plasma: a large number of elementary processes, gas heating, etc.…”