Absorption of electromagnetic waves at oblique resonance in plasmas threaded by inhomogenous magnetic fields

Abstract

There has been significant interest lately in the study of Electromagnetic (EM) waves interacting with magnetized plasmas. The variety of resonances and the existence of several pass and stop bands in the dispersion curve for different orientations of the magnetic field offer new mechanisms of EM wave energy absorption \cite{PhysRevE.105.055209,Juneja_2023,vashistha2020new}. However, earlier studies have investigated only special cases of magnetized plasma geometry (e.g., RL mode $(\vec{k}||\vec{B}_{ext}$) or $(\vec{k}\perp\vec{B}_{ext})$ X,O-mode configuration). In these specific cases, EM waves encounter specific resonances (e.g. for $(\theta=0)$ cyclotron resonances, and for $(\theta=\pi/2)$, hybrid resonances). A general case of EM wave propagation is at an oblique angle with respect to the externally applied magnetic field $\vec{B}_{ext}$ has been considered here. Furthermore, the magnetic field is chosen to be inhomogeneous such that the EM wave pulse encounters a resonance layer within the plasma medium. A 2-D Particle-In-Cell (PIC) simulation using the OSIRIS 4.0 platform has been carried out for these studies. A significant enhancement in absorption leading to almost complete absorption of laser energy by the plasma has been observed. A detailed study characterizing the role of the external magnetic field profile, EM wave intensity, etc., has also been carried out.