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The JET Magnet Power Supplies and Plasma Control Systems

E. Bertolini, P. L. Mondino, P. Noll

Fusion Science and Technology / Volume 11 / Number 1 / Pages 71-119

January 1987

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During a Joint European Torus pulse, the main tokamak loads [the toroidal coils, the transformer coils, the plasma equilibrium coils, and the additional heating devices (not described in this work)] require a total amount of energy of 10000 MJ and a peak power in excess of 1000 MW. The main power source is the U.K.'s Central Electricity Generating Boards' electric power system supplemented by two identical local motor flywheel generators. Since the tokamak loads require a direct-current (dc) supply, the alternating-current power from the energy sources is converted into dc by a combination of thyristor bridges (static units for the plasma position and shaping control, for the additional heating devices, and partially for the toroidal coils) and diode bridges, directly connected to the output of the two generators for the tokamak transformer coils and partially for the toroidal coils. The ohmic heating circuit modulates the flow of power from the flywheel generator to the transformer coils, and its duty is to establish and control the plasma current: It can deliver currents up to 80 kA and supply voltages up to 40 kV. Together with the static units (poloidal vertical, poloidal radial, and poloidal shaping magnetic field amplifiers) to control the plasma position and shape, it constitutes the poloidal circuit. The toroidal circuit is made up of two toroidal field (TF) static units and by the other flywheel generator conventor: It produces and controls the TF current during the pulse, with a maximum current of 67 kA and maximum voltage of 9 kV. The operation of the power supplies is coordinated by the control and data acquisition system (CODAS), which supplies approximate waveforms to each power supply controller, following a predetermined sequence of commands issued by the central timing system. The plasma position and current control is made up of a feedback system built in a conventional way, using magnetic probes and flux loops as sensors and analog electronics for measurement of position, comparitors, and controllers. The control voltages are transmitted to the power sources of the poloidal field to control plasma current, plasma position, and shape. Experimental evidence of the correct functioning of all power supplies and of their control is given by summarizing the key features of a 3.65-MA pulse.

 
 
 
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