Laboratory Experiments on Dispersion and Damping of Kinetic and Inertial Shear Alfven Waves

Details Laboratory Experiments on Dispersion and Damping of Kinetic and Inertial Shear Alfven Waves Laboratory Experiments on Dispersion and Damping of Kinetic and Inertial Shear Alfven Waves

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm23b1401t&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM23B-1401

Physics

2704 Auroral Phenomena (2407), 2772 Plasma Waves And Instabilities (2471), 7829 Kinetic Waves And Instabilities, 7831 Laboratory Studies And Experimental Techniques

Scientific paper

Experiments to test the dispersion relation of shear Alfvén waves as a function of perpendicular wave number were performed using the LArge Plasma Device (LAPD) at UCLA. The waves are launched using a 48-element antenna which can be "tuned" for the perpendicular structure of the Alfvén wave, allowing for good control over the perpendicular wave numbers of the wave. Amplified magnetic search coil probes placed along the length of the chamber are used to measure the wave across the center of the wave pattern. The measured signals are processed to separate the signal into perpendicular wave number components. Signal components at two different locations for the same wave number are cross-correlated and the propagation time with the probe separation leads to the parallel phase velocity for each wave number. Relative amplitudes of each wave number between two probes are also found and allow the damping to be determined. The parallel phase velocity and the damping rate are then compared to the theoretical dispersion relation and damping for both the kinetic and inertial cases. In both the kinetic and inertial limits, the theoretical dispersion relation and damping curves are taken from warm-plasma theory with the inclusion of charged-particle collisional effects via a Krook collision operator. Experimental results in the inertial limit show good agreement with warm-plasma theory when electron-ion collisions are included. In the kinetic limit, good agreement with warm-plasma theory can be achieved only if the effects of electron-ion collisions are reduced significantly. These experimental results will be shown, and the apparent difference in electron-ion collision effectiveness for the two shear Alfvén wave limits will be discussed.

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