Validation of Impurity Ion Flows Measured by Coherence Imaging Spectroscopy in the Compact Toroidal Hybrid*

Two-dimensional profiles of line-integrated impurity emissivity and velocity in the Compact Toroidal Hybrid (CTH) experiment are obtained with Coherence Imaging Spectroscopy (CIS), a polarization interferometry technique. CIS ion velocities inferred in CTH are on the order of 5 km/s and have been validated by comparison with two dispersion spectrometers yielding good agreement to well within the CIS and spectrometer measurement error bars of 2 and 3 km/s, respectively, for multiple sightlines within the CIS field of view. The CIS-observed flow response to a complete reversal of the magnetic field and current directions is limited, indicating ion flows in CTH are determined by other factors. CIS measurements utilizing current-drawing probes in the plasma edge indicate a 5 km/s reversal of the edge ion flow. Ion flow measurements with varying probe currents and magnetic field configurations along with contributions from other parameters, such as external magnetic fields and thermal drifts, are presented.