An investigation of neutral effects on ion cyclotron wave propagation in the Auburn Linear Experiment for Space Plasma investigations.

摘要

Low-frequency electromagnetic waves are of central importance to space plasmas, influencing the processes within space-bound plasmas from the solar corona to the Earth's ionosphere. Knowledge of the basic properties of wave propagation through a plasma is of fundamental importance to understanding these plasma processes. These waves communicate information about changes in magnetic field topologies, and are especially important in the dynamics of magnetic reconnection. Of interest is how the propagation characteristics of these waves change as they travel in the Earth's lower ionosphere and in the solar photosphere, where the neutral population becomes significant. The Auburn Linear Experiment for Space Plasma Investigations (ALESPI) is a cylindrical, linear machine capable of producing partially ionized, high density, low temperature plasmas analogous to a photospheric plasma. These parameters allow the study of wave propagation in a plasma regime where the theory is applicable to both this laboratory plasma and a lower density space plasma. The high density, low temperature, quiescent plasma allows detailed study of both shear and compressional waves. In this experiment, the propagation of nonaxisymmetric electromagnetic waves bounded by the vacuum vessel is studied in a plasma with a significant neutral fraction, similar to an ionospheric plasma. The purpose of this investigation is to predict the properties of these waves, especially near and below the ion cyclotron frequency, as these waves propagate outward along the magnetic field lines from a magnetic reconnection event. To accomplish this goal, a wave is produced in a laboratory plasma and allowed to propagate along the plasma column. The magnitude of the magnetic fluctuation due to these waves is then measured at varying distances from the emitter. The dispersion of the wave is analyzed and compared to a model of the wave propagation through a simple bounded plasma. The variation in the fluctuating magnetic field as a function of radius is also investigated and compared to the model. It is shown in this dissertation that in addition to the neutral density and resistivity having a large affect on the dispersion of the traveling wave, it is also necessary to include the temperature-dependent magnetoacoustic wave in the model in order to conform to the experimental data.