Kinetic thermal ion effects on maintaining high beta plasmas above the Mercier criterion in the Large Helical Device

Abstract

It is found that kinetic thermal ions have a significant stabilizing effect on Large Helical Device (LHD) plasmas from the kinetic magnetohydrodynamic (MHD) simulations. The simulation results for the LHD plasmas at high magnetic Reynolds number show that the high beta plasmas can be maintained since the saturation level of the pressure-driven MHD instabilities is significantly reduced by the kinetic thermal ions. This results from the fact that the response of the trapped ions to the instabilities is weakened by the precession drift motion in the three-dimensional magnetic field. Thus the supercritical stability of the LHD plasmas well above the Mercier criterion can be attributed to the precession drift motion of the trapped ions in the three-dimensional magnetic field.