AC operation of JET tokamak: modification of the JET poloidal field system

The authors report on the preparation and technical performance of experiments on the JET (Joint European Torus) tokamak aimed at producing one cycle of alternating plasma current. After analyzing the revised scenario of the poloidal field circuit in relation to the different phases of the plasma current discharge they report in detail on the modification of the JET poloidal field system. Preliminary experiments successfully demonstrated, at large plasma current, one full cycle of an AC tokamak operation. The two half cycles are characterized by the same Z_eff and the same radiated power at the same density, and the same reaction rate for the same ICRH (ion cyclotron resonance heating) power. A short dwell time, primarily determined by the vertical stray field and the prefill pressure, was demonstrated. The experiment indicates that the duration of the plasma current reversal phase in this mode of operation is dominated by the plasma current rampdown and the plasma current rise