Argon impurity pumpout by ICRF waves in C-Mod L- and I-mode plasmas

Pumpout of argon ions by ICRF waves has been observed in C-Mod deuterium L- and I-mode plasmas with substantial hydrogen dilution. Previous work on C-Mod analyzed this effect through the observed reduction of core argon x-ray brightness. Up to a 90% reduction on time scales of ~10ms follows injection of ICRF power. Time traces for different lines-of-sight suggests that this effect is stronger at mid-radius than in the plasma center. This motivates the need to invert the brightness data into inferred impurity charge state density profiles to understand where impurities are being pumped out and how many ions are being pumped out. C-Mod x-ray and VUV spectroscopy data are used to constrain ImpRad, a Bayesian optimization framework that samples transport coefficient inputs into the AURORA impurity transport forward model until synthetic brightness profiles from inferred density profiles match the experiment. TORIC and CQL3D simulations are performed to calculate the ICRF power coupled to the argon. We hypothesize that, at an optimal hydrogen-to-deuterium ratio, the ICRF heats the argon increasing the radial excursion of the banana orbits until the ions drift out of the plasma. To confirm this, the ASCOT full-orbit solver is used to track argon ion trajectories during pumpout.