Braking due to non-resonant magnetic perturbations and comparison with neoclassical toroidal viscosity torque in EXTRAP T2R

The application of three-dimensional (3D) resonant magnetic perturbations, for the purpose of controlling edge localized modes (ELMs) in high confinement (H-mode) tokamak fusion operations, routinely leads to a significant reduction of the plasma density during the discharge, a phenomenon termed 'density pump-out'. Understanding the density pump-out phenomenon due to 3D fields is a longstanding challenging issue. This work reports a selfconsistent toroidal model that allows initial value simulation of the density pump-out effect. The model successfully reproduces pump-out phenomenology in DIII-D ELM suppression experiments. The radial particle flux, associated with the 3D neoclassical effects (the neoclassical toroidal viscosity, NTV), is found to play an important role in producing the observed large density pump-out. The key physics is associated with the drift kinetic Landau resonances between the toroidal precession of trapped thermal ions and electrons from one side, and the magnetic field perturbation from the other side. Such resonances, occurring near the top of the pedestal region, substantially enhances the radial particle flux associated with NTV. As a general consequence of the resonant NTV flux, larger density pump-out occurs in plasmas with lower collisionality and slower toroidal rotation.

Section: Role Of Particle Flux Ambipolaritymentioning

confidence: 89%

Role of 3D neoclassical particle flux in density pump-out during ELM control by RMP in DIII-D

Liu

Paz-Soldan

et al. 2020

“…Plasma flow damping, induced by non-axisymmetric magnetic fields, has been observed on many devices [16][17][18][19][20][21][22]. Modelling results indicate that the neoclassical toroidal viscous (NTV) torque plays a potentially important role.…”

Section: Introductionmentioning

confidence: 99%

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

Zhang¹,

Liu²,

Piovesan³

et al. 2020

In ASDEX Upgrade hybrid discharges, it is found that an externally applied n = 1 field preferentially distorts the plasma in the core, leading to significant flow damping there and elsewhere across the plasma radius. MARS-F/Q modeling of a neoclassical toroidal viscous NTV) torque that results from an amplified internal kinktype displacement in the plasma core is qualitatively consistent with the measured internal displacements, beta dependence, and rotation damping. 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 q 0 to 1. No appreciable flow damping is found for a β N 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 q 0 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, 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. ‡ Deceased Toroidal modelling of core plasma flow damping by RMP fields in hybrid discharge on ASDEX Upgrade2

“…The NTV in tokamaks with toroidal non-axisymmetry has been of great interest in the fusion research community due to its importance to understand the physics of kinetic plasma response to the applied 3D fields and to effectively utilize the 3D fields as a control method of tokamak performance. As such efforts, a number of experiments on the physics of NTV have been conducted in the various tokamak devices along with significant theoretical and numerical progresses [4][5][6][7][8][9][10][11][12]. A common observation in the 3D tokamak experiments is an alteration of toroidal plasma rotation toward neoclassical offset [13], of which characteristics depend on the operational conditions.…”

Section: Introductionmentioning

confidence: 99%

Observation of resonant and non-resonant magnetic braking in then= 1 non-axisymmetric configurations on KSTAR

Kim

Choe

et al. 2017

Toroidal rotation braking by neoclassical toroidal viscosity driven by non-axisymmetric (3D) magnetic fields, called magnetic braking, has great potential to control rotation profile, and thereby modify tokamak stability and performance. In order to characterize magnetic braking in the various 3D field configurations, dedicated experiments have been carried out in KSTAR, applying a variety of static , 3D fields of different phasing of , 0, and . Resonant-type magnetic braking was achieved by phasing fields, accompanied by strong density pump-out and confinement degradation, and explained by excitation of kink response captured by ideal plasma response calculation. Strong resonant plasma response was also observed under phasing at , leading to severe confinement degradation and eventual disruption by locked modes. Such a strong resonant transport was substantially modified to non-resonant-type transport at higher , as the resonant particle transport was significantly reduced and the rotation braking was pushed to plasma edge. This is well explained by ideal perturbed equilibrium calculations indicating the strong kink coupling at lower is reduced at higher discharge. The 0 phasing fields achieved quiescent magnetic braking without density pump-out and confinement degradation, which is consistent with vacuum and ideal plasma response analysis predicting deeply penetrating 3D fields without an excitation of strong kink response.