Ion kinetic effects on linear pressure driven magnetohydrodynamic instabilities in helical plasmas

Abstract

The linear MHD (magnetohydrodynamic) stability for high beta plasmas in the inward shifted Large Helical Device (LHD) configurations has been investigated for a wide range of magnetic Reynolds numbers $S$ using numerical simulations based on the kinetic MHD model with kinetic thermal ions where the beta is the ratio of the plasma pressure to the magnetic pressure. It is found that the dependence of the linear growth rate of the resistive ballooning modes on the $S$ number changes from $\unicode[STIX]{x1D6FE}\propto S^{-1/3}$ to $\unicode[STIX]{x1D6FE}\propto S^{-1}$ by the kinetic thermal ion effects so that the resistive ballooning modes are significantly suppressed as the $S$ number increases. For a high $S$ number comparable to experimental values, the most unstable modes are interchange modes. The kinetic thermal ion effects change the most unstable interchange mode from the ideal mode to the resistive mode. This transition of the interchange modes by kinetic thermal ion effects is consistent with the shift of the marginal stability boundary for the ideal interchange modes observed in the LHD experiments.

Magnetohydrodynamic hybrid simulation model with kinetic thermal ions and energetic particles

“…For the toroidal Alfvén eigenmode (TAE) investigated in this paper, we can conclude that the kinetic thermal ions are essential for β bulk0 =4%, but are not for β bulk0 =1%. With the new kinetic-MHD hybrid simulation presented in this paper, energy channeling from energetic particles to thermal ions through the energetic-particle driven geodesic acoustic mode (EGAM) [46,47] and the stabilization of pressure driven instabilities in the Large Helical Device (LHD) plasmas by the kinetic effects of thermal ions [44,45] have been demonstrated. The energetic-particle distribution function analyses in the simulations of Alfvén eigenmode bursts and frequency chirping have proved to be useful methods for elucidating the nonlinear physical mechanisms [55][56][57].…”

“…This model is similar to that used in Refs. [44,45]. The spatial profile of the TAE simulated with this model is shown in Fig.…”

Precession drift reversal and rapid transport of trapped energetic particles due to an energetic particle driven instability in the Large Helical Device

“…MEGA has been successfully used to study wave-particle interactions in multiple tokamaks [22][23][24][25][26] as well as the LHD. [27][28][29][30] In this work, an m=n ¼ 1=1 EIC mode is not observed, which may be due to the fixed boundary condition chosen or other effects that will be investigated in a later study. This Letter is instead focused on the destabilization of an m=n ¼ 2=1 mode, closer to the plasma center than the EIC, by an anisotropic population of energetic particles in a high-performance deuterium LHD plasma.…”

Simulations of energetic particle driven instabilities in CFQS

“…The energetic particles are described by the drift-kinetic equations. The modules of gyrokinetic approach is included in MEGA, but the gyrokinetic module is turned off in the simulations presented in this paper, because of three reasons: (1) the Larmor radius of energetic particle ρ EP in CFQS is very small and the product of the perpendicular wave number and ρ EP is much less than the unity; (2) normally the mode linear properties like frequency and mode structure are only weakly influenced by finite Larmor radius effect [17,18]; and (3) drift-kinetic approach is more efficient for computing A c c e p t e d M a n u s c r i p t resources. The δf particle-in-cell (PIC) method is applied, and the equations of motion for each marker particle are solved using a fourth order Runge-Kutta method.…”