On magnetic islands and drift surfaces in Helias configurations

This work is devoted to the study of magnetic islands and resonances of drift surfaces which can take place in the magnetic field of a Helias configuration and which affect the particle confinement properties. It is shown that due to internal magnetic field perturbations which are periodic in major and minor circumference of the torus large islands occur in the magnetic configuration and, in particular, in the drift surfaces. In contrast to external perturbations which arise from errors in the coil system and which can be kept below a tolerable level these internal perturbations may originate from the the finite beta effect or - in the time dependent case - from MHD instabilities in the plasma. In the present analysis the amplitude of these perturbations is considered as an arbitrary parameter. The paper summarizes the results of numerical computations with time independent magnetic perturbations leading to island formation in magnetic surfaces and drift surfaces of alpha particles. (orig.)13 refs.Available from TIB Hannover: RA 71(2/340) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman