Date of Award

Spring 2003

Document Type

Restricted Thesis

Terms of Use

© 2003 Matt Landreman. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Physics & Astronomy Department

First Advisor

Michael R. Brown

Abstract

In plasma physics it is a commonly cited and often valid approximation that magnetic fieldlines are "frozen" to the plasma fluid. However, in certain situations in solar and astrophysics, as well as in fusion engineering, this approximation of "ideal magnetohydrodynamics" leaves out important physical processes. Large gradients in the field can arise, causing effects that were previously negligible to become significant, and allowing the fieldlines to slip through the plasma. Mysteriously, this "magnetic reconnection" effect appears to be much more significant than a back-of-the envelope calculation would suggest. Reconnection is investigated in the Swarthmore Spheromak Experiment (SSX), a laboratory plasma device. The reconnecting field configuration in SSX is both largely reproducible and also more three-dimensionally complicated than in previous experiments elsewhere. The principle diagnostic discussed herein utilizes an array of small pick-up loops to measure the magnetic field. Use is made of a novel inexpensive highspeed multiplexing data acquisition system, which for the first time permits observations of a plasma's complicated dynamics in all three dimensions and their variation from shot to shot. Custom visualization software has been developed to explore the complicated four-dimensional datasets. The magnetic probe exhibits an uncertainty of 2%, and it correctly reproduces the theoretical expected fields for simple known current geometries. The probe provides evidence that both a driven and a slower steady-state variety of reconnect ion do in fact occur in SSX, and several unique three-dimensional properties distinguish the plasma configuration from previous "two-dimensional" experiments. An unfortunate inherent curvature in the geometry prevents conclusive testing of a magnetic quadrupole phenomenon reported in recent computational studies of collisionless reconnection. Various higher-order terms in the generalized plasma Ohm's law can be computed, suggesting that the J x B Hall force and the pressure gradient force may be the key phenomena in SSX among those neglected in ideal magnetohydrodynamics. Reconnection is correlated with the detection of high-energy ions emanating from the site of spheromak collision. Recent modifications to the SSX device to permit "full-merging" of the plasma have produced images of a more tempestuous and less controlled reconnection geometry, although the physical processes involved seem to be the same as those in the original configuration.

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