Electric power circuit for plasma stabilization in ASDEX Upgrade

ASDEX Upgrade, a reactor-relevant divertor tokamak now under construction at Garching, requires a sophisticated plasma stabilization system for both the horizontal and vertical position control owing to the strongly elongated plasma. On the basis of nonlinear circuit simulation it is shown that 4-quadrant, phase-controlled thyristor converters operating in circulating-current control mode can meet these requirements. Two pairs of stabilizating coils for active plasma position control are installed. That pair of coils, located between the vacuum vessel and toroidal coils, are inductively coupled to the plasma in a way such that in the event of plasma disruption, a current would be induced in the coil which exceeds the maximum permissible coil current limit. To avoid this, two force-commutated DC thyristor circuit breakers connected in series with these coils are installed. Maximum current and voltage per circuit breaker: 30 kA/1.6 kV. In addition, a pyrobreaker protects the coils in case of malfunctioning of the thyristor switch or the current control system. A short overview of the fast digital controller will also be given, together with the present status of construction. (author). 8 refs.; 10 figs