Model of heat deposition during fast discharge tests of the ITER toroidal field model coil

In the framework of the ITER (International Thermonuclear Experimental Reactor) project, the TFMC (Toroidal Field Model Coil) has been manufactured by European industry, using about 800 m of a 80 kA Nb₃Sn cable-in-conduit conductor to wind the 98 turns of the coil. These turns are wound in 10 pancakes which are inserted inside machined stainless steel radial plates, and the whole winding pack is enclosed in a thick stainless steel casing. These passive conductive structures are expected to experience severe induced eddy currents and associated Joule heating during the last testing phase of the TFMC, when fast discharges are triggered to study the electromagnetic and thermal-hydraulic transient behavior of the coil. Diffusing through insulation, the Joule heating induced in the radial plates will add to the AC losses induced in the superconducting cable. The AC losses along the TFMC winding pack are deduced from accurate magnetic field computations performed by the 3-D magneto-static code TRAPS, the eddy currents are calculated with an analytical model using circuit equations, and the Joule heating diffusion is studied with a 1-D thermal analysis model. Using these heat loads as input data, the helium temperature and pressure increases in the conductor are computed with the finite element code GANDALF. The possibility of a quench of the whole magnet is discussed.