Argon 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 [1]. Time traces for different spectrometer lines-of-sight suggests that this effect is stronger at mid-radius than in the plasma center. X-ray and VUV data is therefore inverted to infer impurity charge state density profiles to understand where in the plasma impurities are being pumped out and how many ions are removed. This is done using ImpRad, a Bayesian optimization framework that samples transport coefficient inputs into the AURORA impurity transport forward model until synthetic brightness profiles match the experiment [2, 3]. We hypothesize that, at an optimal hydrogen-to-deuterium ratio, the ICRF directly heats the argon increasing the radial excursion of the banana orbits until the ions drift out of the plasma, causing pumpout. To confirm this, the ASCOT4-RFOF full-orbit solver is used to track argon ion trajectories during RF heating [4]. We will present analysis comparing experimentally inferred argon density profiles against predicted density and brightness profiles from turbulent, neoclassical, and orbit loss transport calculations. We then extrapolate these results to envisage an optimized scheme to actively pumpout tungsten in SPARC.



Work supported by US DOE under DE-SC0014264



[1] J.E. Rice et al., 2022 NF, accepted May 9, 2022

[2] F. Sciortino et al., 2021 PPCF 63 112001

[3] F. Sciortino et al., 2020 NF 60 126014

[4] S. Sipilä et al., 2021 NF 61 086026