Upgrading the JET Magnet System for 7MA Plasma

JET was designed for a plasma current of 5 MA and has operated successfully at that level. To enable JET to produce meaningful DT plasmas, it is necessary to upgrade the machine performance.¹ The paper describes the effects on the poloidal and toroidal magnet systems of increasing the plasma current to 7 MA. It has not been necessary to increase the toroidal field but operation at higher plasma current increases the torque loading on the coils. In the case of the poloidal coils an increased flux swing is required so the magnetising current has been increased by 50%. Effects considered include magnetic forces and mechanical and thermal stresses in the coils. Modifications to the coil system and improvements to the power supplies that enable the new performance to be achieved are described. It is concluded that a 7 MA plasma current is feasible.