Electromagnetic analyses on radial field sector coils for JT-60SA

In the framework of EU – JA “Broader Approach” Agreement, the JT-60SA satellite tokamak will be built in Naka, Japan. In JT-60SA, to achieve the steady-state high beta plasma, suppression of Resistive Wall Modes (RWM) is necessary. Therefore, a passive stabilizing plate and a RWM active control system based on in-vessel coils are foreseen for JT-60SA. In the present design, this system consists in 18 sector coils, 6 in the toroidal, 3 in the poloidal direction, rated for a maximum current of 2.5 kA and fed by a dedicated fast power supply system. The coils shall produce sufficient radial magnetic field at the plasma edge, and the active control system shall be fast enough to react in real time to the plasma instabilities. In addition, during fast transients of the plasma current, significant loop voltage could be induced along the sector coils, which could result in over-currents in the coils and in the power supplies. This paper deals with the electromagnetic analyses on the sector coils of JT-60SA, with the main aim to determine the voltage/current characteristic of the coils and, at the same time, to have a first estimation of amplitude and shape of the produced magnetic field; different sector coil design solutions were considered and evaluated. The studies on the coil over-currents during plasma disruption or vertical displacement events are also presented. The results give useful indications in support to the development of the sector coils and power supply design and the identification of their electrical and functional requirements.