High magnetic field cryogenic coil for the Frascati Tokamak transformer

The Frascati Tokamak transformer is made up of a system of coils magnetically linked with the toroidal plasma column of the machine. The main element of this setup is a 1.2 m long solenoid, inner diameter 0.3 m, outer diameter 0.7 m. The flux density on the solenoid centerline, at a 31 kA current, is 17 Tesla. The energy stored in the transformer is 30 MJ. The current variation produced opening a commutating switch generates a maximum voltage of 40 kV across the transformer, of this about 28 kV across the solenoid. Ionization and heating of the plasma are produced by the corresponding emf induced along the plasma column.