O. Neubauer(1) and U. Braunsberger(2)
(1)Institut fur Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Juelich, Germany
(2)Institut fuer Hochspannungstechnik, Technische Universitaet Braunschweig, Postfach 3329, D-38023 Braunschweig.
Forschungszentrum Juelich "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 coil sets on the inboard side of the TEXTOR-94 vessel, each with four helical conductors. Two additional conductors are needed for compensation purposes. The coil sets will be energized by a 4-phase current at selected frequencies (DC, 50Hz and a band between 1 kHz and 10 kHz). By counterconnection of phase 1 with 3 and phase 2 with 4, respectively, 8 load circuits plus one for the compensation coils will be formed.
For operation in the range 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.
In the ideal case the 16 coils are arranged in 16 equidistant toroidal steps, thus compensating the inductive 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 each system gets a remaining fraction of the coupled voltages from its neighbours. In this case a system of 9 inductively coupled resonant circuits has to be fed.
To determine the required parameters of the power supplies the whole matrix of inductive coupling factors has to be calculated. Since there are no analytical solutions for this geometry, numerical calculations methods have been used together with measurements. The voltages resulting from the 4-phase current in the coil sets and the coupling matrix form an asymmetric system. The additional coil pair located at the top and the bottom of the DED coils is necessary to compensate this effect.
The operating conditions for the desired currents each require a different set of voltages, compensating currents and capacitors which has to be calculated before operation. The transient behaviour of the system and the influence of tolerances and failures have to be investigated.
A central control unit with an appropriate algorithm has to be established. The results of parameter calculations and simulations as well as measurements of the described system are presented.