Electron heating mechanism in radio-frequency microhollow cathode discharge in nitrogen

Abstract

A two-dimensional particle-in-cell/Monte-Carlo code has been developed to study the electron heating mechanism in radio-frequency microhollow cathode discharge (rf-MHCD) operated in nitrogen at 100 Torr. The influence of secondary electron emission coefficient (γ) on the electron density and total ionization rate, the occurrence of α ionization rate and γ ionization rate, and the electron heating rate are calculated. The results show that compared with the condition of γ = 0, the maximum electron density at γ = 0.1 shows an increase of 60% and the maximum total ionization rate increases by nearly one order of magnitude, which indicates secondary electron heating in rf-MHCD plays an important role. Through the detailed distribution of γ ionization rate and α ionization rate by two-electron model, it is found that γ ionization rate is about 90% of the total ionization rate and the spatial distribution of γ ionization rate presents the same characteristics of the total ionization rate. Therefore, we can further confirm secondary electron heating is the main heating mechanism in rf-MHCD. From the distribution of electron heating rate, it also shows the decisive role of secondary electron heating. With the increase of γ coefficient, α ionization rate increases. This means the electrons which are from fast electron group transferred into slow electron group in the plasma are heated again by sheath oscillation and do contribute to the occurrence of α ionization collision.