Date of Degree
PhD (Doctor of Philosophy)
Craig A. Kletzing
Two sets of related experiments are presented here. In the first, measurements of shear Alfvén waves are used to test the predictions of a variety of different electron collision operators, including several Krook collision operators as well as a Lorentz collision operator. New expressions for the collisional warm-plasma dielectric tensor resulting from the use of the fully-magnetized collisional Boltzmann equation are presented here. Theoretical predictions for the parallel phase velocity and damping as a function of perpendicular wave number k⊥ are derived from the dielectric tensor. Laboratory measurements of the parallel phase velocity and damping of shear Alfvén waves were made to test these theoretical predictions in both the kinetic (vte ≫ vA) and inertial (vte ≪ vA) parameter regimes and at several wave frequencies (ω < ωci). Results show that in the inertial regime, the best match between measurements and theory occur when any of the Krook operators are used to describe electron collisions. In contrast, the best agreement in the kinetic regime is found when collisions are completely ignored.
In the second set of experiments, whistler waves were launched and received by a pair of dipole antennas immersed in the plasma at two positions along the background magnetic field. According to cold-plasma theory, there is absorbtion of the whistler wave when ω = |ωce| = eB/me due to resonance with the electrons. The whistler frequency was swept from somewhat below up to the electron cyclotron frequency |ωce|. As the frequency was swept, the wave was resonantly absorbed by those parts of electron phase space density which were Doppler shifted into resonance. The transmission of the wave through the plasma was measured. This measurement of transmission can be converted into a measure of the parallel electron distribution function. This diagnostic is designed to attempt to measure modifications to the parallel electron distribution function due to interactions with inertial Alfvén waves.
Copyright 2009 Derek Jon Thuecks
Thuecks, Derek Jon. "Laboratory investigations of dispersive Alfvén waves and their role in electron acceleration." dissertation, University of Iowa, 2009.