CQL3D-GENRAY Simulations of Suppression of Impurity-Induced Current Quench Using LHCD in C-Mod
Abstract
In Alcator C-Mod lower hybrid current drive experiments (LHCD), Reinke has examined discharges which undergo an abrupt thermal quench (TQ) to low Te due to radiation from incoming tungsten flake material. This is simulated using the coupled CQL3D Fokker-Planck/Ampere-Faraday and GENRAY ray tracing codes, based on experimental traces of the background densities, temperatures, and one-turn voltage. Simulations show evolution of a quasilinear plateau on the electron distribution, and with onset of the TQ, a collisional decay of the plateau from lower to higher velocity (τslow ~v3) giving an inverted distribution, and consequently a self-consistent instability of the injected LH waves; this broadens the current profile by edge damping. The effect of broadening is similar to recently-reported MHD TQ healing in DIII-D discharges. The LH C-Mod interpretation further supports a new, hopefully robust, disruption control approach.
Supported by USDOE/OFE under Grants DE-SC0018090, DE-SC0016452, DE-FG02-04ER54744, DE-FG02-95ER54309.- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- 2020
- Bibcode:
- 2020APS..DPPB11013H