Toroidal modelling of core plasma flow damping by RMP fields in hybrid discharge on ASDEX Upgrade

Toroidal modelling of core plasma flow damping by RMP fields in hybrid discharge on ASDEX Upgrade

Toroidal modelling of core plasma flow damping by RMP fields in hybrid discharge on ASDEX Upgrade 150 150 UKAEA Opendata
UKAEA-CCFE-PR(20)05

Toroidal modelling of core plasma flow damping by RMP fields in hybrid discharge on ASDEX Upgrade

Resistive plasma response to the n = 1 (n is the toroidal mode number) RMP field is systematically investigated for a high-beta hybrid discharge on ASDEX Upgrade. Both linear and quasi-linear response are modelled using the MARS-F and MARS-Q codes, respectively. Linear response computations show a large internal kink response when the plasma central safety factor q0 is just above 1. This internal kink response induces neoclassical toroidal viscous (NTV) torque in the plasma core, which is significantly enhanced by the precessional drift resonance of thermal particles in the super-banana regime. Quasi-linear simulation results reveal a core plasma flow damping by about 25%, agreeing well with experimental observations, with the NTV torque playing the dominant role. Sensitivity studies indicate that the internal kink response and the resulting core flow damping critically depend on the plasma equilibrium pressure, the initial flow speed, the coil phasing and the proximity of q0 to 1. No appreciable flow damping is found for a low betaN plasma. A relatively slower initial toroidal flow results in a stronger core flow damping, due to the enhanced NTV torque. Weaker flow damping is achieved as q0 is assumed to be farther away from 1. Finally, a systematic coil phasing scan finds the strongest (weakest) flow damping occurring at the coil phasing of approximately 20 (200) degrees, again quantitatively agreeing with experiments. This study points to the important role played by the internal kink response in plasma core flow damping in high-beta hybrid scenario plasmas such as that foreseen for ITER.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IOP (Institute of Physics)
Published date:
23/06/2021
The published version of this paper is currently under embargo and will be available on 28/07/2021