Impurity transport mitigation via electron cyclotron heating in the Prototype-Material Plasma Exposure eXperiment (Proto-MPEX)

Proto-MPEX is an existing linear device, the prototype of the Material Plasma Exposure eXperiment (MPEX). The latter is currently under construction at ORNL to address the challenges of plasma-material interactions (PMI) in a high duty-cycle and safe operating fusion reactor. In this work, a coupled SOLPSCOMSOL-->GITR workflow, which we call "Simulated Transport of RF Impurity Production and Emission (STRIPE)", has been developed and employed to study the erosion and redeposition of Al impurities in Proto-MPEX. Recent experiments on the Proto-MPEX, shows significant amount of impurities, generated from the helicon window, deposit at the target for helicon-only conditions. This study investigates the mitigation of impurity release and its transport in Proto-MPEX via electron cyclotron heating (ECH). Increased edge temperature due to the ECH leads to an increased ionization in the periphery of the device. This along with the strong parallel transport and temperature screening effect due to the overall increase in plasma temperature, has found to significantly reduce the radial movement of Al-impurity and thereby, its transport towards Proto-MPX target (small central region with 0.02m radius whereas device radius is 0.1m ). Furthermore, a shorter connection length between the target and the RF-antenna also reduces the radial impurity transport and leads to the avoidance of impurity deposition at the target. These findings provide possible solutions to mitigate impurities transport in MPEX.