Speaker
Description
The superconducting (SC) magnets used to confine the plasma in nuclear fusion reactors must be first cooled from 300 K down to ~4-5 K, then kept sufficiently below the current sharing temperature during the tokamak pulsed operation, in order to preserve their SC properties. For that purpose, a He refrigerator is used. During the cooldown, it provides the boundary conditions (He temperature THe and mass flow rate dm/dt) at the coil inlet; during operation, the pulsed heat load coming from the magnets must be suitably removed by the refrigerator and smoothed to avoid operation instabilities.
In order to develop an adequate computational model for both scenarios, we consider here as reference refrigerator configuration that of the ITER CSMC facility, at Naka, Japan, used for 15+ years to test the performance of full-scale ITER cable-in-conduit conductors in conditions relevant for real tokamak operation. The Collins cycle operated by the CSMC refrigerator features two stages: the first one, assisted by LN2 precooling, from 300 K to 80 K, the second, based on two isentropic expansions in turbines and an isenthalpic J-T valve, from 80 K to 4 K.
After the recent development of a model for the 300 K --> 80 K stage, here we present a model of the CSMC refrigerator aimed at the 80 K --> 4 K stage. The simulated THe, pressure and dm/dt at relevant locations, as well as controller outputs and valve openings, during a CSMC cooldown turn out to be in good agreement with the measurements.
