Two-dimensional model of current density and temperature in the T.F. coils of the Tokamak de Varennes during long pulse operation

To prepare for the different operational modes of the toroidal field (T.F.) power supply, we have calculated the equipotentials, current density and isotherms of a T.F. coil using a 2-d finite element algorithm. The results show that, for the model we have considered and in the absence of cooling, the hottest point will reach a temperature of 90 degrees C in 12 s at maximum current, well below a maximum temperature of 105 degrees C permissible for the insulator. The ramp-up and ramp-down phases are 2 s each (equivalent to 1 s at full current), but leaves 10 s or 30 s of operation, respectively, at maximum current. The cooling reduces the central leg average temperature to 58 degrees C, the hot point temperature to 70 degrees C and relaxes the temperature gradients at the joint boundaries, leaving the hottest point in the joint nearly unaffected