Low frequency Alfven waves induced by toroidal flows

The magnetohydrodynamic (MHD) spectra of toroidally rotating, axisymmetric tokamaks are analyzed. The continuous spectrum equations for the coupled lo calized Alfven and slow modes are derived. The effect of flow on this spect rum is threefold: Doppler shift, centrifugal, and Coriolis effects enter. B y exploiting a low-beta, large aspect ratio expansion, the newly found low frequency Delta m=0 Alfven gap [van der Holst , Phys. Rev. Lett. 84, 2865 ( 2000)] located on the rational mode surfaces is analyzed. This gap is creat ed by the geodesic curvature of the field lines, together with finite press ure, and by centrifugal and Coriolis effects. It is determined by a three m ode interaction involving a central Alfven mode and two sideband slow modes . From the same scheme, another new purely flow-induced gap inside the Delt a m=0 gap is found. Also, toroidal flow-induced Alfven eigenmodes (TFAE) ar e found in the Delta m=0 gap. All of these waves may be useful for MHD spec troscopy. Since the gap structures as well as the global wave are in the lo w frequency regime, they will have important implications for stability. (C ) 2000 American Institute of Physics. [S1070-664X(00)05410-0].