Whistler waves in plasmas with magnetic field irregularities: Experiment and theory

Abstract

The properties of whistler waves propagating in a large laboratory magnetoplasma with magnetic field irregularities have been studied. Two types of ambient magnetic field inhomogeneities have been considered: (i) a localized “lenslike” perturbation and (ii) an elongated “ductlike” irregularity. The magnetic field was perturbed by immersing into the plasma, without creating any significant plasma density disturbances, additional current-carrying coils. It has been found that the presence of magnetic field irregularities causes the whistler wave’s diffraction and affects their patterns substantially. Plasma regions with locally enhanced magnetic field strength focus oblique whistlers; oppositely, local magnetic field minima debunch the whistler waves. In case of prolonged magnetic field irregularity formation—encompassing several whistler wavelengths along its size—the diffraction effects are distinctly pronounced; even the comparatively weak magnetic field disturbances at the level of 10% lead to strong modifications of the whistler waves’ pattern. Theoretical calculations are presented which confirm the related experimental measurements. The obtained results are of great importance for laboratory plasmas as well as magnetospheric physics, and represent a new look at the problem of whistler waves’ scattering and ducting, caused not by the plasma density ducts and gradients, but by magnetic field irregularities.