Calculations for the coupled resonant circuits of the dynamic ergodic divertor coils at TEXTOR-94 and consequences for their power supplies

“Forschungszentrum Julich” and the partners of the “Trilateral Euregio Cluster” (TEC) have developed a concept for the Dynamic Ergodic Divertor (DED) at TEXTOR-94. The DED introduces a new element to the idea of the Ergodic Divertor (ED) which, at TORE SUPRA, demonstrated its benefits in improved radiation efficiency of impurities and better impurity screening. The coil arrangement of the proposed DED consists of four sets of coils on the inboard side of the TEXTOR-94 vessel, each with four helical conductors. The coils set will be energized by a 4-phase current of up to 15 kA at selected frequencies (DC, 50Hz and from 1 kHz to 10 kHz). The inductive fraction of the coil voltages will be supplied by series capacitors thus forming resonant circuits and considerably reducing the dimensions of the power supply. An ideal coil configuration of 16 equidistant toroidal steps shows no coupling between the 4-phase systems. At TEXTOR-94 the DED coils of one set start and end at the same toroidal angle. Due to edge effects there is a residual coupling increasing the reactive power and forcing a transfer of active power. In this case a system of coupled circuits has to be fed. The inductances have been determined. Consequences and solutions for the power supplies have been derived. The final design comprises two compensation coils located at the top and the bottom of the DED coils as well as precisely tuned capacitors and decoupling transformers to compensate the effects of asymmetry