Thermal ion kinetic effects and Landau damping in fishbone modes

Abstract

The kinetic–magnetohydrodynamic (MHD) hybrid simulation approach for macroscopic instabilities in plasmas can be extended to include the kinetic effects of both thermal ions and energetic ions. The new coupling scheme includes synchronization of the density and parallel velocity between thermal ions and MHD, in addition to pressure coupling, to ensure the quasineutrality condition and avoid numerical errors. The new approach has been implemented in the kinetic-MHD code M3D-C1-K, and was used to study the thermal ion kinetic effects and Landau damping in fishbone modes in both DIII-D and NSTX. It is found that the thermal ion kinetic effects can cause an increase of the frequencies of the non-resonant $n=1$ fishbone modes driven by energetic particles for $q_\mathrm {min}>1$ , and Landau damping can provide additional stabilization effects. A nonlinear simulation for $n=1$ fishbone mode in NSTX is also performed, and the perturbation on magnetic flux surfaces and the transport of energetic particles are calculated.

The role of fast ions in spontaneous neoclassical tearing mode instabilities in NSTX

“…Ideal modes have been theoretically suggested asthe implicit trigger for spontaneous NTMs [9]. In the NSTX discharge #134020, the ideal mode is calculated to be unstable using the particle in cell/MHD hybrid code M3D-C1-K [14]. The input thermal and fast ion pressure profiles obtained from TRANSP are consistent with those used in section 3.…”

“…The ideal mode predicted using M3D-C1-K is pressure driven [14]. The fast ion pressure is 17% of the total pressure, and that removing the fast ion pressure results in the simulated growth rate going imaginary.…”

“…The input equilibria are consistent with The frequency and growth rate of an ideal mode calculated using M3D-C1-K for the scaled q 0 . Redrawn from figure 13 of [14]. Measured mode frequency and q 0 in black horizontal and vertical lines, with the shaded area indicating the measurement uncertainty for q 0 .…”

“…Simulated ideal mode frequency and growth rate in asterisk and square, connected with dotted lines for visualization. [14] © Cambridge University Press. Reprinted with permission.…”

“…Therefore, this fast ion effect is important for an NTM to overcome the stabilizing ion polarization current in its early growth phase, even though it does not directly explain the formation of a seed island. Moreover, a simulation has shown that fast ions can even affect the onset phase, by indirectly driving the ideal modes [14] which can provide a seed island implicitly [9].…”