Modeling of the ECCD injection effect on the Heliotron J and LHD plasma stability

J Varela,K Y Watanabe,S Yamamoto,A Azegami,L Garcia,K Nagasaki,K Nagaoka,D A Spong,A Cappa

doi:10.1088/1741-4326/abad84

Abstract

The aim of the study is to analyze the stability of the energetic particle modes (EPM) and Alfven Eigenmodes (AE) in Helitron J and LHD plasma if the electron cyclotron current drive (ECCD) is applied. The analysis is performed using the code FAR3d that solves the reduced MHD equations describing the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particle (EP) species, including the effect of the acoustic modes. The Landau damping and resonant destabilization effects are added via the closure relation. The simulation results show that the n = 1 EPM and n = 2 global AE (GAE) in Heliotron J plasma can be stabilized if the magnetic shear is enhanced at the plasma periphery by an increase (co-ECCD injection) or decrease (ctr-ECCD injection) of the rotational transform at the magnetic axis (). In the ctr-ECCD simulations, the EPM/AE growth rate decreases only below a given , similar to the ECCD intensity threshold observed in the experiments. In addition, ctr-ECCD simulations show an enhancement of the continuum damping. The simulations of the LHD discharges with ctr-ECCD injection indicate the stabilization of the n = 1 EPM, n = 2 toroidal AE (TAE) and n = 3 TAE, caused by an enhancement of the continuum damping in the inner plasma leading to a higher EP β threshold with respect to the co- and no-ECCD simulations.

Highlights

The external injection of electron cyclotron waves (ECW) [1, 2] modifies the plasma stability of nuclear fusion devices by the generation of non inductive currents in the plasma
electron cyclotron current drive (ECCD) injection in LHD [19] attains the stabilization of the energetic-ion-driven resistive interchange mode (EIC) [20, 21], Toroidal and global Alfven eigenmodes (TAE / Global Alfven Eigenmodes (GAE)) [22] as well as pressure gradient driven modes [23]
The aim of the present study is to simulate the stabilization of the energetic particle modes (EPM), Global Alfven Eigenmodes (GAE) and Toroidal Alfven

Summary

Introduction

The external injection of electron cyclotron waves (ECW) [1, 2] modifies the plasma stability of nuclear fusion devices by the generation of non inductive currents in the plasma. ECCD injection in LHD [19] attains the stabilization of the energetic-ion-driven resistive interchange mode (EIC) [20, 21], Toroidal and global Alfven eigenmodes (TAE / GAE) [22] as well as pressure gradient driven modes [23]. NBI lines parallel to the magnetic axis are injected in LHD plasma with an energy of 180 keV and a power of 16 MW [34]. The LHD device has two NBIs perpendicular to the magnetic axis injected in the plasma periphery with an energy of 32 keV and a power of 12 MW [35]. The aim of the present study is to simulate the stabilization of the energetic particle modes (EPM), Global Alfven Eigenmodes (GAE) and Toroidal Alfven.

Numerical scheme

Equilibrium properties

Simulations parameters

Conclusions and discussion