Measurements of the Internal Magnetic Field and n=3 Level Populations of Injected Deuterium Using the B-Stark Motional Stark Effect Diagnostic on DIII-D

We describe the latest results from the newly upgraded B-Stark diagnostic system installed on the DIII-D tokamak. This system is a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of the Stark-split $D_\alpha$ emission from injected neutral beams. We present a thorough study of the performance of the diagnostic in measuring the magnitude and direction of the internal magnetic field over a range of plasma conditions. Measurements were made with toroidal fields in the range $1.2-2.1$ T and plasma currents in the range $0.5-2.0$ MA. We also present results from a study of the level populations of the $n=3$ state of the injected deuterium neutrals over a range of plasma densities, $1.7-9.0 \times 10^{13}~{\rm m}^{-3}$, and neutral beam voltages, $50-81$ keV. These results are compared against the calculations from an atomic physics code, part of the ADAS package.