Engineering aspects of the ISTTOK operation in a multicycle alternating flat-top plasma current regime

The main engineering aspects of the tokamak ISTTOK operation in a multicycle alternating flat-top plasma current regime are presented. AC discharges have been obtained feeding the ohmic and vertical magnetic field circuits with a specially designed alternating power supply, based on a single electrolytic capacitor bank and a fast insulated gate bipolar transistor (IGBT) H-bridge, feedback controlled by a discreet power DAC. The horizontal magnetic field has been created by an independent and pre-programmable DC power supply. The optimization of AC operation has also implied the installation of a new set of symmetric and more external windings for the vertical B-field and of an adequate gas puffing system. Discharges with seven half-cycles and flat-top plasma currents of about ±4 kA without dwell times were already achieved, in a total time span of 240 ms approximately equal to five times the maximum duration of a single DC discharge.