Design and construction of demountable circular coil with high current density contacts

Demountable coils in fusion devices like spherical Tokamaks are seen as a necessity for future devices as frequent replacement of components are foreseen. In D-shaped Toroidal Field (TF) multi turn coils low current density contacts can be used as they do not strongly affect the magnetic field in the plasma. For circular multi-turn coils low current density contacts can heavily affect the magnetic field of the plasma. High current density contacts are prone to material transfer between contacts or even damage due to bridging of the contacts. In this paper we report the design and construction of a 4-turn circular TF coil using high current density contacts, designed to withstand currents of the order of 10 kA with current densities of the order of 75 kA/cm² for pulse duration of 60 MS.