Effect of the magnetic field on the electron kinetics under AC/DC electric fields: benchmark calculations and electron cyclotron resonance

Abstract

This work presents a numerical study of the electron kinetics under AC/DC electric fields and DC magnetic fields crossed at arbitrary angles. The physical phenomena are studied both in model gases (Reid-ramp and Lucas-Saelee) and in real gases (N2 and Ar). The simulations are carried out with an upgraded version of the Monte Carlo open-source code LoKI-MC. The code is compared against several independent benchmark calculations available in the literature. In addition, new benchmark calculations for electron kinetics solvers are produced in conditions of coexistent AC electric and DC magnetic fields, accounting for the effect of the crossing angle between the fields and discriminating the evolution along the AC cycle. The role of the magnetic field is discussed, distinguishing the configurations with DC and AC electric fields. In DC electric fields, the oscillatory motion caused by the magnetic field decreases the efficiency of the electron acceleration, which manifests on the power absorbed by the electric field and on the electron mean energy. Notably, an exceptional behavior is found in Ar for small regions of E/N and B/N , where: for constant B/N , the mean energy decreases with increasing E/N ; and, for constant E/N , it increases with increasing B/N . These phenomena were firstly reported by Ness and Makabe in 2000 and are now confirmed by means of Monte Carlo simulations. In AC electric fields, when the magnetic field value is such that the electron cyclotron frequency is similar to the angular frequency of the electric field, the synchronization of the cyclotron motion with the electric field enhances electron acceleration, through the well-known electron cyclotron resonance. However, for conditions where the mean collision frequency is much higher than the cyclotron frequency, the synchronization tends to breakdown and the magnetic field is detrimental for the electron acceleration, as in the DC electric field case.