Argon pumpout by ICRF three-ion heating in Alcator C-Mod and WEST

Pumpout of argon (Ar) ions by ICRF waves has been observed in C-Mod deuterium L- and I-mode plasmas with substantial hydrogen dilution, with a reduction in Ar reaching up to 80% [1]. X-ray and VUV spectroscopy are used 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 measurements match the experiment. The analysis is repeated using atomic data from ADAS, FLYCHK, and SCRAM to illustrate errors in interpreted transport using different data sources. The inferred density profiles agree well with the turbulent transport code TGLF when the ICRF is off, but significantly differ when the ICRF is on. These Ar experiments were then repeated in WEST confirming that pumpout is triggered at an optimal hydrogen-to-deuterium ratio as well as illustrating the dependence on ICRF frequency. TORIC5 simulations of the ICRF electric fields support transport analyses for both C-Mod and WEST shots. In this talk we will discuss the physics of the observed Ar pumpout and will discuss the potential to utilize a three-ion heating scenario to actively pumpout tungsten in SPARC.



Work supported by US DOE under DE-SC0014264. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

[1] J.E. Rice et al., 2022 Nucl. Fusion, 62 086009