Internal kink mode stabilization and the properties of auxiliary heated ions

The stability of the internal kink mode is analyzed in terms of the essential properties of auxiliary heated ions. A fundamental difference between fusion born alpha particles and auxiliary heated ions is that the latter are typically anisotropically distributed. The effect of anisotropy, which is usually ignored in the fluid contribution of hybrid kinetic-magnetohydrodynamic codes, provides a stabilizing effect for populations that have a large passing fraction. The effect on internal kink mode stability is further modified by crucial finite orbit effects if the distribution is asymmetric in v(parallel to), such as for unbalanced beam ion populations. Additionally, such heating scenarios transfer momentum to the background plasma thereby especially modifying the kinetic response of thermal ions. In contrast, anisotropic distributions with large trapped fractions incur improved kinetic stability, but at the cost of increased fluid instability, which is partially due to the effect of anisotropy on the equilibrium. (C) 2005 American Institute of Physics.