HR: 0800h
AN: NG21B-0524    [Abstracts]
TI: Laboratory experiments on whistler instabilities and triggered emissions
AU: * Urrutia, J M
EM: urrutia@ucla.edu
AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547, United States
AU: Stenzel, R L
AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547, United States
AU: Strohmaier, K D
AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547, United States
AB: Strong electron energization is observed (3 to 30 eV) in propagating whistler spheromaks and stationary relaxing field-reversed configurations [http://www.iop.org/EJ/abstract/0741-3335/49/5A/S02]. It is ascribed to the free electron acceleration by an inductive electric field along the toroidal null line (separator). Non-Maxwellian distributions are observed, and temperature anisotropies are likely. These can give rise to whistler instabilities. Spontaneous excitation of whistler modes with B_wave \ll B₀ are observed (ω/2 π ≈ 7~MHz, v_phase ~eq 1.3× 10⁶~m/s). These magnetic oscillations detach from the whistler spheromak and propagate along and oblique to the ambient magnetic field. Their space-time dependence, polarization, spectra and parameter dependence have been measured. In order to measure the spatial growth rate, small amplitude whistler waves are excited from a separate antenna. It is observed that these trigger a stronger whistler emission at an upshifted frequency. Both convective wave growth against drifting electrons is seen as well as temporal growth in the current layer. Thus the source region exhibits absolute and convective instability mechanisms. These observations are relevant to triggered whistler emissions in the ionosphere and magnetosphere. Work supported by NSF/DOE.
DE: 2772 Plasma waves and instabilities (2471)
DE: 7839 Nonlinear phenomena (4400, 6944)
DE: 7867 Wave/particle interactions (2483, 6984)
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting