"Testing at 4 K and at 80 K are completely different operations," explains David Grillot, ITER deputy program manager for plant systems and former leader of the Cryogenics Section. "Considering that a toroidal field coil's mass is in excess of 300 tonnes, the colder test requires considerable infrastructure—a large cryostat, a dedicated power supply, an electrical feeder and associated instrumentation, and an interface with a large refrigerator located inside the cryoplant. It's not comparable at all to testing at 80 K, which is relatively simple and has been done routinely."
The cold test facility will be located in the partially vacated poloidal field coil winding facility. Supercritical helium at 4 K will be delivered by way of a cryogenic auxiliary cold box (blue) interfacing with the cryoplant; electrical power will be fed by a busbar (orange) originating in a dedicated power supply system. Both cryogens and electrical power will be delivered to the magnet by way of a feeder (yellow). As the coil will be in the horizontal position, a new design is required for connecting it to the feeder.
But the mood has changed and "a window of opportunity" has opened. The
Designed to accommodate the tokamak's D-shaped toroidal field coils, the dimensions of the cold test facility's cryostat (11 m x 22 m) will also allow for the testing of poloidal field coil #1 (10 m in diameter).