STABILIZATION OF EXTERNAL KINK MODES IN A TOKAMAK WITH ROTATING PLASMA

An analytical theory of stabilization of external kink modes in a toka mak with rotating plasma is developed, which is of interest in connect ion with experiments on the DIII-D tokamak demonstrating such a stabil ization. It is assumed that, in addition to the main poloidal harmonic , the mode includes one or more side-band poloidal harmonics with sing ular points lying inside the plasma. Near these singular points, plasm a inertia and related toroidal effects, the compressible part of plasm a pressure and longitudinal viscosity, are allowed for. These effects are described kinetically taking into account the toroidal trapping of the resonant ions, which is essential if the toroidal velocity is sma ll compared to the ion thermal velocity. Thereby, the theory presented includes both ion Landau damping and its weakening due to toroidal tr apping. Near the singular points high-beta effects, which result in th e finiteness of the Mercier index s, are allowed for. It is shown that the influence of plasma rotation on the external kink modes is most s ignificant in the case of s < 0, i.e., when the development of the ins tability in a non-rotating plasma is most highly favored. In this case , the plasma rotation plays a stabilizing role, even when the ion Land au damping is neglected. The analysis presented also confirms the hypo thesis of Bondeson and Ward on the stabilizing effect of ion Landau da mping if this damping is not too small.