Theory and calculation of current profile control near rotational surfaces in a tokamak by electron cyclotron waves

The effect of electron cyclotron current drive (ECCD) on nonlinear resistive magnetohydrodynamic (MHD) perturbations in a tokamak is analyzed. Along the ray trajectories of electron cyclotron wave (ECW) beams injected from the low-field side in the ordinary mode (O-mode) polarization, the power deposition, and current drive efficiencies are calculated using fully relativistic analytical expressions. The driven current is inserted in a consistent theory of nonlinear magnetic island evolution, which provides the scaling of the radio-frequency (RF) driven current required to control magnetic reconnection in terms of the plasma equilibrium parameters and optical properties. It is shown that the threshold for error field driven islands can be increased by ECCD and that the current profile around the q=2 rational surface can be shaped to control the evolution of rotating magnetic islands by modulation of the gyrotron power source. © 1996 American Institute of Physics.