Stabilization of neoclassical tearing modes by electron cyclotron current drive

Abstract

The generalized Rutherford equation for the neoclassical tearing mode is studied. New analytical expressions for the nonlinear stability criterion, the seed island width, and the saturated island width are derived. These are especially useful when the saturated island width is small. A formalism for calculating the current needed to stabilize the mode is established by adding an externally driven current. Inserting the reference parameters of the International Thermonuclear Experimental Reactor (ITER) [ITER-JCT and Home Teams, Plasma Phys. Controlled Fusion 37, A19 (1995)], a value of 160 kA to be driven by Electron Cyclotron Current Drive (ECCD) in order to completely stabilize an m=2 mode is found, well within the capabilities of the ITER ECCD system. If higher currents can be driven, the local βp at the resonant surface can be increased significantly.