Electromagnetic wave transparency of X mode in strongly magnetized plasma

TL;DR

This study demonstrates through simulations that electromagnetic waves in the X mode can pass through strongly magnetized plasma as if it were vacuum, due to particle drift effects preventing charge separation.

Contribution

It reveals that in strongly magnetized plasma, the EM wave transparency occurs because particle motions do not generate charge or current sources, shrinking the stop band to zero.

Findings

EM wave propagates as in vacuum despite plasma presence

Stop band width approaches zero in strong magnetic fields

Particle drifts prevent charge separation and current formation

Abstract

An Electromagnetic (EM) pulse falling on a plasma medium from vacuum can either reflect or propagate inside the plasma depending on whether it is overdense or underdense. In a magnetised plasma, however, there are usually several pass and stop bands for the EM wave depending on the orientation of the magnetic field with respect to the propagation direction. The EM wave while propagating in a plasma can excite electrostatic disturbances in the plasma [1, 2]. In this work Particle - In - Cell simulations have been carried out to illustrate the complete transparency of the EM wave propagation inside a strongly magnetised plasma. The external magnetic field is chosen to be perpendicular to both the wave propagation direction and the electric field of the EM wave, which is the X mode configuration. Despite the presence of charged electron and ion species the plasma medium behaves like a vacuum. The observation is understood with the help of particle drifts. It is shown that though the two particle species move under the influence of EM fields their motion does not lead to any charge or current source to alter the dispersion relation of the EM wave propagating in the medium. Furthermore, it is also shown that the stop band for EM wave in this regime shrinks to a zero width as both the resonance and cut-off points approach each other. Thus transparency to the EM radiation in such a strongly magnetised case appears to be a norm. This may have important implications in astrophysical scenarios. For instance, the plasma surrounding objects like pulsars and magnetars is often threaded with strong magnetic fields.