Rotation braking with n = 1 nonaxisymmetric magnetic perturbation in the EAST tokamak

The influence of energetic particles (EPs) on the ideal internal kink mode, in rotating tokamak plasmas, is numerically investigated by simultaneously solving MHD-kinetic hybrid equations together with a toroidal momentum balance equation utilizing the MARS-Q code (Liu et al 2013 Phys. Plasmas 20 042503). The neoclassical toroidal viscous (NTV) torque, induced by precessional drift resonances of trapped energetic particles, acts as the momentum sink term to damp the plasma flow. Quasi-linear initial value simulations show local reduction of the flow amplitude and enhancement of the flow shear near the q = 1 rational surface (q is the safety factor) due to EP induced NTV. Both effects in turn destabilize the internal kink mode. These numerical findings are robust against the initial linear stability of internal kink, the initial plasma flow profile, as well as the equilibrium distribution model for EPs.

Section: Introductionmentioning

confidence: 99%

Ideal internal kink stability in presence of plasma flow and neoclassical toroidal viscosity due to energetic particles

Zhang¹,

Liu²,

Yu³

et al. 2021

“…Modeling results indicate that the neoclassical toroidal viscous (NTV) torque plays a potentially important role. However, quantitative discrepancy still exists between the predicted NTV and the experimental observation, especially in the plasma core region [18,22]. Besides NTV, other types of toroidal torques due to 3D fields may also play roles in flow damping.…”

Section: Introductionmentioning

confidence: 99%

“…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

“…Figure 11 shows the profiles of the NTV torque density induced by even and odd parity RMPs for the equilibrium with q 95 = 4.5 by NTVTOK code modeling [55]. The NTV torque density induced by even parity RMPs is overall larger than that induced by odd parity RMPs, suggesting stronger effects on edge plasma rotation [56] and perturbation fields penetration [57]. In this case, the NTV torque contributed by ions is comparable to that by electrons, and their directions are The results show that even parity RMPs induce larger NTV torque in the plasma edge with stronger resonant and non-resonant harmonics, which could significantly impact plasma toroidal flow and the penetration of perturbation fields [57].…”

Section: Mode Coupling Effect In Plasma Responsementioning

confidence: 99%

Extension of ELM suppression window using n = 4 RMPs in EAST

Xie

Sun

et al. 2023

Self Cite

The q95 window for Type-I Edge Localized Modes (ELMs) suppression using n=4 even parity Resonant Magnetic Perturbations (RMPs) has been significantly expanded to a range from 3.9 to 4.8 in EAST, which is demonstrated to be reliable and repeatable over the last two years. This window is significantly wider than the previous one achieved using n=4 odd parity RMPs, which is around q95=3.7±0.1. Here, n represents the toroidal mode number of the applied RMPs and q95 is the safety factor at 95% of the normalized poloidal magnetic flux. During ELM suppression, there is only a slight drop in the plasma stored energy and density (≤10%). The comparison of changes in the pedestal profiles suggests that ELM suppression is achieved when the pedestal gradient is kept lower than a threshold. This wide q95 window for ELM suppression is consistent with the prediction made by MARS-F modeling prior to the experiment, which located it at one of the resonant q95 windows for plasma response. The Chirikov parameter taking into account plasma response near the pedestal top, which measures plasma edge stochasticity, significantly increases when q95 exceeds 4, mainly due to the denser neighboring rational surfaces. The modeling of plasma response reveals a strong coupling between resonant and non-resonant components across the pedestal region, which is a characteristic of the kink-peeling like response observed during RMP-ELM suppression in previous studies on EAST. These promising results demonstrate the reliability of ELM suppression using the n=4 RMPs in EAST and expand the physical understanding on ELM suppression mechanism.