MAGNETIC ISLAND CONTROL ON THE COMPACT AUBURN TORSATRON

The understanding and control of magnetic islands is an important issu e in confinement of toroidal plasmas. A series of recent experiments o n the Compact Auburn Torsatron (CAT) [Fusion Technol. 18, 281 (1990)] have investigated the control of magnetic islands. As a by-product, th e minimization of the size of magnetic islands has been accomplished t hrough the application of externally applied error fields. Both the ph ase and amplitude of the applied correction field at a given rational surface are varied in order to control the island chain on a rational surface. The experimental results have been interpreted within the fra mework of a Hamiltonian description of the magnetic field in toroidal geometry. In particular it has been demonstrated that first order pert urbation theory is sufficient to predict the variation of island size for a wide range of externally applied fields. Using this theoretical approach a novel technique of error field determination through the me asurement of the local rotational transform has been developed. The ph ysical mechanisms which lead to spatial spreading of the electron beam used in the surface mapping have also been studied.