Ion Temperature and Flow Velocity Measurements on SSX-FRC

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2005
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Swarthmore College. Dept. of Physics & Astronomy
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Thesis (B.A.)
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Full copyright to this work is retained by the student author. It may only be used for non-commercial, research, and educational purposes. All other uses are restricted.
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Abstract
An Ion Doppler Spectroscopy (IDS) diagnostic was used to measure the flow velocity and temperature of a plasma created by SSX-FRC. The diagnostic was based on the principles of Doppler spectroscopy, namely, that the wavelength of a moving light source is shifted proportional to its velocity and the width of an emission line varies with temperature. The emission line at 229.7 nm of Carbon III, an impurity ion in the hydrogen plasma, was imaged and its location and width measured. The IDS system being a work in progress, the minimum resolvable linewidth is higher than the linewidth we expect to see based on previous experiments and so detailed temperature and velocity measurements could not be carried out. SSX's PMT's allow detailed time resolution and the plot of temperature variation with time shows that the width of the line peaks between 30 and 50 J1S before it drops to the minimum resolvable width. Considering the basic plasma physics of the system, it is thought that the wide line is due to velocity shear: oppositely directed jets resulting from magnetic reconnect ion create both a red- and a blue-shifted emission line, which overlap and are imaged as a single, very wide, line. A simple analytical model of a fluid system with velocity shear was created to investigate whether or not shear could cause the widening. The lineshapes this model returned were wide and double-peaked due to overlap, supporting the shear hypothesis.
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