Laboratory Experiments on Whistler Wave Interactions with Energetic Electrons

摘要

Whistler wave excitation in plasmas has been modeled in a laboratory experiment. The most efficient coupling is achieved with magnetic loop antennas which can deposit 50% of the applied energy into waves in a dense plasma with low ambient magnetic field. Since space plasmas are dilute, it is suggested to eject an expanding plasma plume into space for efficient wave excitation with a small magnetic antenna. The ejected waves have magnetic fields exceeding the ambient field. The properties of such nonlinear whistler modes have been investigated. Their propagation speed depends on amplitude and field topology, they can steepen into whistler shocks and strongly accelerate electrons. In the presence of neutrals, the energetic electrons produce visible light emission. Anisotropic electron distributions are formed which create whistler instabilities and emissions at different frequencies than applied. Scattering of electrons in phase space is evident.