STABILIZATION OF THE IDEAL m = 1 INTERNAL KINK BY ALPHA PARTICLES AND ICRF HEATED IONS

摘要

The plasma potential energy δW_(tot) associated with m = 1 internal kink displacements is calculated for JET equilibria, taking into account the presence of alpha particles and ions heated by ion cyclotron resonance frequency (ICRF) waves. In the latter case the heated ion distribution is modelled as a simple function of ICRF parameters, which is consistent with numerical Fokker-Planck calculations. It is likely that the kink energy is an important parameter in determining the properties of sawtooth oscillations: in the ideal limit, positive values of δW_(tot) indicate that kink displacements are stable. Alpha particles give rise to a stabilizing kinetic term in δW_(tot), but also exert a destabilizing influence owing to their effect on the Shafranov shift. The alpha particle contribution to δW_(tot) is found to be destabilizing when the central value of the safety factor q_0 = 0.75, but stabilizing when q_0 = 0.9. The effect of ICRF heated minority ions can be calculated in terms of fluid and kinetic corrections to δW_(tot). Both trapped and passing ICRF heated ions play a significant stabilizing role. Complete stabilization of the ideal kink mode, due to either alpha particles or ICRF heated ions, is most easily achieved if q_0 lies close to unity or if the radius of the q = 1 surface is small.