Date of Award

Spring 2007

Document Type

Restricted Thesis

Terms of Use

© 2007 Vernon H. Chaplin. 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

David H. Cohen

Second Advisor

Michael R. Brown

Third Advisor

Christopher D. Cothran

Abstract

We present 1 μs time resolution calculations of the electron temperature of the Swarthmore Spheromak Experiment (SSX) plasma during magnetic reconnection. The non-LTE excitation kinematics code PrismSPECT is used to simulate emission spectra for a variety of plasma conditions. These model spectra are compared to experimental data from two main diagnostics: a vacuum ultraviolet (VUV) monochromator and a low-resolution soft x-ray detector (SXR). Analysis of simulation results reveals that the plasma quickly (< 10 μs) approaches equilibrium conditions in the density regime of interest; as a result we can safely use steady-state simulations for comparisons with the data. Measured UV line strength ratios depend primarily on the electron temperature in the plasma, so we are able to use measurements of carbon impurity emission lines in conjunction with SXR measurements as a temperature diagnostic. In particular, the C III 97.7 nm / C IV 155 nm line intensity ratio proves to be extremely useful, while the C III 229.7 nm line appears anomalously strong in experimental measurements. Measurements of oxygen and nitrogen lines allow us to conclude that the carbon/ oxygen number ratio in SSX is approximately 1000/ 1, while nitrogen concentrations are negligible. Temperatures derived from the 97.7 nm / 155 nm line ratio average 20 eV for single spheromak shots and 20 eV early in counter-helicity shots, increasing to 35 eV after the two spheromaks merge. SXR measurements suggest a mean electron temperature of 30-35 eV for single spheromak shots and 40 eV for counter-helicity merging. The counter-helicity temperature profile shows a distinct peak at t ~40 μs, the time at which reconnect ion is believed to occur; however, the timing of this peak is not in precise agreement with the peak in the average temperature profile derived from carbon line ratios.

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