Performance of cable-in conduit conductors in ITER toroidal field coils with varying heat loads

The toroidal field (TF) coils in the International Thermonuclear Experimental Reactor (ITER) will operate with varying heat loads generated by AC losses and nuclear heating. The total heat load is estimated to be 2 kW per TF coil under normal operation and can be higher for different operating scenarios. AC losses are caused by ramping the poloidal field (PF) for plasma initiation, burn, and shutdown; nuclear heating results from neutrons that penetrate into the coil past the shield. Present methods of reducing or eliminating the losses lead to larger and more expensive machines which are unacceptable with present budget constraints. A suitable solution is to design superconductors that operate with high heat loads, using a cable-in-conduit conductor (CICC), which can operate with such loads. Two thermal analysis design codes have been used to study the thermal response in a CICC conductor for the ITER TF coils. The analysis verifies that the mass flow rate through the coils affects the temperature margin and shows that a true steady-state flow is not established in the coils for the flow rates and operating conditions expected. Studying the transient response of the helium to a 100-s plasma burn is the first step taken toward determining the helium exiting conditions during a normal operating scenario