Nonlinear electron magnetohydrodynamic physics. VI. Magnetic loop antenna across the ambient field

Abstract

Laboratory experiments on nonlinear whistler phenomena near a magnetic loop antenna with axis across the magnetic field are presented. The field topologies, radiation efficiency, electron energization and instabilities in the low-frequency whistler regime have been investigated. The time-dependent magnetic fields are fully three-dimensional. Radial and spiral magnetic null points are produced near the antenna but not in the propagating wave fields whose amplitudes can exceed that of the ambient field. Electron energization and light emissions are observed near the antenna. The electron drift excites whistler emissions at frequencies higher than the applied frequency. Source region and propagation characteristics of these waves have been investigated. The results are important for understanding nonlinear effects of loop antennas in plasmas and nonlinear effects in strong whistler turbulence.