Investigations on the feedback system of ASDEX

The plasma position in ASDEX will be safeguarded from radial displacement by a thyristor-operated vertical field control circuit, from vertical displacement by a radial field control circuit with power transistors. In both control circuits the electrodynamic properties of the non-circular, slit vacuum vessel with its divertor inserts play a big role. The essential magnetic couplings and time constants were therefore determined in a model of ASDEX. These dynamic properties and the inter-related plasma physics are represented by means of feedback technology. The control processes are computed by the root locus method and Laplace transformation. For optimizing purposes, use is made of graphic methods such as conformal mapping in Nichols diagrams. The problems entailed in fast feedback control with thyristors are thereby given special attention