Evolution of Isotopic Purity During Hydrogen Campaign in DIII-D *

A recent hydrogen campaign at DIII-D involved switching the dominant hydrogenic fuelling species from deuterium to hydrogen and then back to deuterium. Due to strict isotopic purity constraints, efforts were put towards conditioning the walls using multiple actuators. Connections between isotopic ratios in the core and diverter of the tokamak and various experimental inputs were studied, including plasma shape, gas puff, glow time, vessel baking, boronization, and heating power.  Three primary diagnostics were used: midplane spectroscopy for the measurements in the plasma core, a high resolution multi-chord diverter spectrometer with multiple view chords along the diverter, and a neutron scintillator to measure neutron generation to obtain a volume averaged concentration of the deuterium.