Isothermal internal kink instability in a toroidally rotating tokamak plasma

The properties of the internal kink instability in a tokamak with a toroida lly rotating plasma is analysed from the ideal magnetohydrodynamic (MHD) eq uations, for plasmas satisfying an isothermal equation of state. The plasma equilibrium is assumed to have large aspect ratio, circular cross section, poloidal beta value (beta(p)) of order unity, and a rotational frequency c omparable to the sound frequency. For an isothermal plasma, the rotational effect on the internal kink mode can be expressed in terms of a 'rotational beta value' (beta(Omega)) of the plasma. This quantity is defined in the s ame way as beta(p), with the kinetic energy density of the rotation (u(Omeg a)) replacing the plasma pressure. The rotation is found to be strongly sta bilizing if u(Omega) is an increasing function of the minor radius (beta(Om ega) < 0). In the opposite case, the rotation is destabilizing unless the p ressure profile is much more peaked than the kinetic energy density profile . (C) 2000 Elsevier Science B.V. All rights reserved.