High Resolution Flow and Ion Temperature Measurements with Ion Doppler Spectroscopy at SSX
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2006
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Swarthmore College. Dept. of Physics & Astronomy
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Thesis (B.A.)
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Abstract
The Swarthmore Spheromak Experiment (SSX) studies magnetic reconnect ion by merging co- and counterhelicity
spheromaks. Typical plasma parameters include electron density ne rv 1015 cm-3 , temperature
Ti + Te rv 30 eV, and magnetic fields IBI rv 0.1 T. This thesis documents the construction of a new highresolution
ion Doppler spectroscopy (IDS) diagnostic. The SSX IDS system features a 1.33 m Czerny-Turner
spectrometer with a 316 grooves/mm echelle grating and a 32-channel photomultiplier tube array. On any
shot, we can observe any of 10 different chords through the plasma with submicrosecond time resolution and
an instrument temperature rv 3 eV. Current studies have focused on the evolution of the carbon III 229.687
nm line which we observe at 25th order, with dispersion 0.0085 nm/mm using 3.7x magnifying exit optics.
We have determined the time dependence of flow velocities and ion temperatures in the plasma. We have
also performed Abel inversions to determine radial profiles of the plasma emissivity. In addition, we have
observed near-Alfvenic bi-directional flows due to reconnection. These results, as well as a possible model
for the flows based on shear, are presented.