LHCD Suppression of Impurity-Induced RE Current Quench in C-Mod Simulated with CQL3D-GENRAY

In Alcator C-Mod lower hybrid current drive experiments (LHCD), Reinke [1] has examined rare discharges which undergo an abrupt thermal quench (TQ) to low Te due to radiation from incoming tungsten flake material. The plasma current is maintained nearly constant, and the discharge recovers from the TQ. This is simulated using the coupled CQL3D Fokker-Planck/Ampere-Faraday [2] and GENRAY ray tracing codes, based on experimental traces of the background densities, temperatures, and one-turn voltage, with Zeff an adjustable parameter aimed at keeping Ip at the experimental value. Simulations show that the LHCD and collisional absorption broadens the current density profile. The effect of broadening is similar to recently-reported MHD TQ healing in DIII-D discharges [3]. These simulations support a new, hopefully robust, disruption control approach. [1] M.L. Reinke et al., Nucl. Fusion 59, 066003 (2019). [2] R.W. Harvey et al., Nucl. Fusion 59, 106046 (2019) [3] X.D. Du et al., Nucl. Fusion 59, 094002 (2019); X. D. Du, Personal communication (2020).