Control of tearing modes in toroidal fusion experiments using "designer" error fields

It is demonstrated that a magnetic island chain formed by a saturated teari ng instability in a toroidal magnetic fusion device can lock to a special c lass of externally generated magnetic perturbation in a stabilizing phase. The theoretical apparatus needed to design such perturbations is outlined. These special perturbations-which are termed "designer" error fields-could be used to control the amplitudes of tearing modes in toroidal magnetic fus ion experiments without the requirement of fast phase modulation. This type of control would be far more feasible in a reactor environment than conven tional active feedback control via external magnetic perturbations. (C) 200 1 American Institute of Physics.