HR: 0800h
AN: NG21B-0525    [Abstracts]
TI: Observation of Gendrin modes in a laboratory plasma
AU: * Strohmaier, K D
EM: kyle@physics.ucla.edu
AF: Department of Physics and Astronomy, UCLA, Box 951547, Los Angeles, CA 90095-1547, United States
AU: Urrutia, J M
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
AB: Gendrin or constant velocity modes are whistlers with oblique phase velocity and parallel group velocity. They exist for ω< ω_c/2, have an angle \cos θ_G = 2ω/ ω_c, parallel phase and group velocities v_gr=v_ph =(c/2)ω_c/ω_p and a frequency-independent wavelength λ=c/f_p. The modes are important for wave particle interactions in the ionosphere and magnetosphere since even without ducting they have no energy spread along \mathbf B₀, hence provide for long interaction lengths. We have excited Gendrin modes in a large laboratory plasma with a magnetic loop antenna of diameter D~eq λ at ω~eq 0.3 ω_c. The linear waves develop a conical phase front whose surface normal \mathbf{k} makes an angle θ =52° ~eq θ_G. A conical surface is not a plane wave but a superposition of all Gendrin modes on the 3-D refractive index surface. The cones translate along \mathbf{B}₀ with little change indicating a parallel energy flow. By integrating the energy density over a cross section transverse to \mathbf{B}₀, the wave damping is obtained and normalized to k_i/k_r~eq 0.03 which shows that both collisional and Landau damping are small. Since the phase velocity is close to the thermal velocity, this implies that the parallel electric field is small, i.e., the inductive electric field is opposed by a space charge electric field. 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