Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm51a1283u&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM51A-1283
Other
2487 Wave Propagation (0689, 3285, 4275, 4455, 6934), 2723 Magnetic Reconnection (7526, 7835), 2772 Plasma Waves And Instabilities (2471)
Scientific paper
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.
Stenzel R. L.
Strohmaier K. D.
Urrutia Jorge
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