Dynamics of rotating tearing modes under phase locked feedback control

Low-order single-helicity rotating resistive modes in a tokamak can, in principle, be stabilized in amplitude by means of externally applied fields, provided that control of the phase difference between mode and field is achieved. Possible feedback loop schemes are presented and the non-linear dynamics is studied analytically and numerically. Other physical effects currently observed in modern tokamaks are discussed and interpreted in the general framework of phase locking phenomena.