Aspects of driven reconnection of low order modes in tokamaks

In tokamaks an important case of driven reconnection is due to the action of time varying external fields with helical pitch resonant with q=m/n rational magnetic surfaces. Such fields may be created for control purposes or exist as ''error fields'' due to machine imperfections. To design a control system it is important to know the plasma response to oscillating fields in a finite frequency band, and also the role of nonlinear coupling of rotating islands. Novel aspects of these two problems are presented. (orig.)