Ballooning instabilities in Tokamaks with sheared toroidal flows
The ballooning-mode eikonal representation is applied to the linearized incompressible magneto-hydrodynamic (MHD) equations in axisymmetric systems with toroidal mass flows to obtain a set of initial value partial differential equations in which the time and the poloidal angle are the independent variables. The description of the instability, however, is incompatible with normal mode solutions of the MHD equations because the wave vector becomes time dependent when the velocity shear is finite. The effects of sheared toroidal flows on localized ballooning can be investigated because the initial value formulation of the problem does not constrain the solutions to evolve as exp (iwt). Fixed boundary MHD equilibria with isothermal toroidal flows that model the JET device are generated numerically with a variational inverse moments code. As the initial value equations are evolved in time, periodic bursts of ballooning activity are observed which are correlated with the formation of a ballooning structure at the outside edge of the torus that becomes displaced by 2(pi) in the extended poloidal angle domain from one burst to the next. The frequency of these bursts depends only on the velocity shear and the instability growth rates extracted from the peak values of the bursts are virtually linear. The velocity shear has a stabilising influence on plasma ballooning.
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion, Vol. 30 (1988), No 13, pp. 1805-1812
Record Number: 198910195 / Last updated on: 1994-12-01
Original language: en
Available languages: en