HR: 0800h
AN: SM51A-1283    [Abstracts]
TI: Dissipation of Magnetic Energy Into Electron Heating and Ion Acceleration Near Magnetic Loop Antennas
AU: * Urrutia, J
EM: urrutia@ucla.edu
AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547 United States
AU: Strohmaier, K D
SM51A-1283 AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547 United States
AU: Stenzel, R L
SM51A-1283 AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547 United States
AB: Low frequency whistler waves are excited with magnetic loop antennas in a large laboratory plasma (1 m diam, 2.5 m length, 10¹² cm^-3, 5 G). Strong light emission is observed on every other half cycle of the applied sinusoidal loop current. Internal probe measurements reveal that electrons are heated when the wave magnetic field creates magnetic null points. These prevent the magnetic energy from propagating in the whistler mode. Such null points are formed when the axial component of the rf magnetic field opposes and exceeds the ambient field, which occurs for one polarity of the rf field. In the other polarity the magnetic energy propagates in the whistler mode without significant dissipation. Time-resolved measurements show that the electron heating starts near the antenna and propagates radially inward and axially outward from the loop, roughly following the pattern of the electron current. In addition to electron heating, a density perturbation is observed near the loop. During the rise of the loop current, the electrons perform an E × B drift away from the loop wire. This creates a strong space charge electric field which accelerates the ions away from the loop. A density cavity is created around the loop wire. Bursts of energetic ions are inferred from time-of-flight measurements. Depending on time and spatial scales, the density perturbations can modify the induced electron currents, hence effect the wave excitation. Both electron heating and ion acceleration dissipate some of the applied rf energy, hence reduce the radiation efficiency. Work supported by the Air Force Research Laboratory.
DE: 2487 Wave propagation (0689, 3285, 4275, 4455, 6934)
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2772 Plasma waves and instabilities (2471)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005