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Description
The JT-60SA tokamak fusion experiment is under final commissioning at Naka, Japan. The magnetic confinement of this fusion facility is performed by superconducting magnets cooled around 4.5 K. The JT-60SA magnet system is composed of toroidal field (TF) magnets, central solenoid (CS), and equilibrium field (EF) magnets. There are 18 TF magnets (Nb-Ti conductor, max field at conductor 5.65 T), which, along with their structures, represent a mass of 420 tons. There are 6 EF magnets (Nb-Ti conductor, peak field 6.2 T) weighing 178 tons. The CS consists of 4 modules (Nb3Sn conductor, peak field 8.9 T) and weighs 100 tons.
These magnets are kept in their superconducting state by a forced-flow circulation of supercritical helium (SHe) ensured by two separated cooling loops. The SHe flows into these loops by the means of cryogenic circulators and ensure a temperature of around 4.5 K to the magnets inlet. The first loop (mass flow rate circulating 900 g/s) is cooling in parallel the TF magnets and in series, their structures, and the CS structures. The second loop (mass flow rate circulating 1 kg/s) is cooling in parallel the CS and EF magnets. The heat deposited in or created by the magnets and their structures is removed through the SHe loops by the cryogenic plant able to extract about 9 kW equivalent at 4.5 K.
This work presents the thermal-hydraulic model of the SHe cooling loops and the superconducting magnets circuits to predict their behavior, particularly in the event of a fast safety discharge (FSD). The comparison of the modeling and FSD experimental measurements provide inputs to ensure that the loops and the refrigerator can cope with a FSD of magnets without endangering the facility. The modeling of the loops is developed using Simcryogenics, a cryogenic simulation tool developed by CEA/DSBT. The modeling of the loops is a step towards the complete modeling of the whole cryomagnetic system of JT-60SA to improve the control of key variables for a more reliable operation.
| Submitters Country | france |
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