Study of Alfvén eigenmode stability in Quasi-Poloidal Stellarator (QPS) plasma using a Landau closure model

Abstract

The aim of this study is to analyze the linear stability of Alfvén Eigenmodes (AE) in QPS device heated by a tangential NBI. The analysis is performed using the gyro-fluid code FAR3d, that solves the reduced MHD equations for the thermal plasma coupled with moments of the kinetic equation for the energetic particles (EP). The AE stability is calculated in several operational regimes of the tangential NBI: EP β between 0.001 − 0.1, EP energy between 12−180 keV and different radial locations of the beam. The analysis is performed for vacuum and finite β equilibria as well as QPS configurations with 2 and 3 periods. The EP β threshold in the vacuum case is 0.001 and the AE frequency is lower as the energy of the EP population decreases. Toroidal Alfvén Eigenmodes (TAEs) with f = 80 − 120 kHz and Elliptical AE (EAEs) between f = 120 − 350 kHz are triggered between the middle-outer plasma region (r/a > 0.5). The AE stability improves in the simulations with finite β equilibria and 3 period configurations with respect to the vacuum case with 2 periods because the continuum gaps are slender, leading to a higher threshold of the EP β, above 0.03 for the AEs triggered by the helical mode families. Helical effects are not strong enough to destabilize Helical Alfvén Eigenmodes (HAEs), the AEs with the largest growth rates are triggered by the n = 1 and n = 2 toroidal families.

Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma

“…In addition, the nonlinear version of the code was applied in the analysis of sawtooth-like events, internal collapse events, EIC burst and MHD burst observed in LHD plasma [63,64,[79][80][81][82] as well as the AE saturation in DIII-D plasma [62]. The AE stability in plasma with multiple EP species for LHD, DIII-D, ITER and CFETR plasma [53,54,83] as well as predictions of the AE stability in future devices as JT60SA [84] and new devices exploiting different symmetries of the magnetic trap as CFQS and QPS [71,85] were also analyzed using the FAR3d code.…”