Effect of ECH/ECCD on energetic-particle-driven MHD modes in helical plasmas

Abstract

The effect of electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) on energetic-particle (EP)-driven magnetohydrodynamic (MHD) modes is studied in the helical devices LHD, TJ-II and Heliotron J. We demonstrate that EP-driven MHD modes, including Alfvén eigenmodes (AEs) and energetic particle modes (EPMs), can be controlled by ECH/ECCD. In the LHD device, which has a moderate rotational transform and a high magnetic shear, co-ECCD enhances toroidal AEs (TAEs) and global AEs (GAEs), while counter-ECCD stabilizes them, which improves the neutron rate compared with the co-ECCD case. Counter-ECCD decreases the core rotational transform and increases the magnetic shear, strengthening the continuum damping on the shear Alfvén continua (SAC). In the TJ-II device, which has a high rotational transform, moderate magnetic shear and low toroidal field period, helical AEs (HAEs) appear when the HAE frequency gap of the SAC is changed by counter-ECCD combined with a bootstrap current and neutral-beam-driven current. On the other hand, both co- and counter-ECCD are effective in stabilizing GAEs and EPMs in the Heliotron J device, which has a low rotational transform and low magnetic shear. The experimental results indicate that the magnetic shear has a stabilizing effect regardless of its sign. Modeling analysis using the FAR3d code shows that the growth rates are reduced by both co- and counter-ECCD in Heliotron J, reproducing the experimental results. ECH only affects EP-driven MHD modes, and the experimental results show that the effect depends on the magnetic configuration. In Heliotron J, some modes are stabilized with an increase in ECH power in the low-bumpiness magnetic configuration, while some modes are destabilized in the high- and medium-bumpiness magnetic configurations.

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

“…On the other hand, the ECCD is not injected in the Heliotron J discharge 61484, showing unstable n = 1 EPM and n = 2 GAE. In addition to the reference cases, a set of equilibria are calculated modifying the rotational profile mimicking the effect of the ECCD for different current drive intensities and orientations [7,48]. The electron density and temperature profiles are reconstructed by Thomson scattering data and electron cyclotron emission.…”

“…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. In particular, the electron cyclotron current drive (ECCD) [3][4][5][6][7] can improve the stability of the pressure/current gradient driven modes and the Alfven Eigenmodes (AE) in tokamaks [8][9][10][11][12][13] and Stellarators [14][15][16][17][18].…”

Summary of the 27th IAEA Fusion Energy Conference in the categories of EX/W, EX/D, and ICC

“…The ECH effect on energetic particle modes (EPMs) and global Alfvén eigenmodes (GAEs) is reported from Heliotron J [8]. ECH power is scanned from 120 kW to 280 kW shot by shot to study the influence of ECH on EP-driven instability.…”

Suppression of toroidal Alfvén eigenmodes by the electron cyclotron current drive in KSTAR plasmas

“…The correlation between performance degradation and AE activities has been investigated widely. At present-day experiments, various AE control tools such as electron-cyclotron (EC) waves, external magnetic perturbations and fast-ion pressure gradient change have been investigated and tested in tokamaks [20][21][22][23][24][25][26] and helical devices [27][28][29][30]. Among the various control tools, the electron cyclotron current drive (ECCD) is one of the most promising techniques because a flexible deposition of the EC waves is possible on the location where the AEs are excited.…”

“…Among the various control tools, the electron cyclotron current drive (ECCD) is one of the most promising techniques because a flexible deposition of the EC waves is possible on the location where the AEs are excited. Particularly it has been found that the current drive effect in the helical devices is more apparent [27][28][29][30] than in the tokamaks since the plasma current level in tokamaks is substantially high.…”