AC Losses in the Second Module of the ITER Central Solenoid

The ITER Central Solenoid (CS) will be realized by assembling a stack of six modules. Each module is a solenoid consisting of 40 pancakes wound with a Nb
₃
Sn Cable in Conduit Conductor (CICC). The tests of the second module (CSM#2) were performed at the General Atomics (GA) facility in Poway (US). During the test campaign, the CS Module is submitted to dumps of the transport current from different initial values (10, 15, 20, 25, 30, 35, 40 kA) to 0 kA, which allow measuring the AC losses in the coil. In this paper we present the results on AC losses during the dumps from different initial transport currents, as computed with two different methods. The first method is based on the observation that the dumps determine a very fast pressure rise of the supercritical helium embedded in the module, which undergoes an isochoric transformation. This approach is therefore based on the computation of the variation of internal energy of the helium during the pressure rise itself. The second method is based instead on a calorimetric procedure aimed at estimating the enthalpy variation of the supercritical helium due to the thermal power deposited during the current dumps. The main contribution to the losses during these dumps is due to the coupling losses. As for the hysteresis losses in the magnet, the results obtained through slow current cycle tests are also presented.