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Description
CTRFR-1 (Compact Tokamak-based Repetitive Fusion Reactor-1, R = 1 m, a = 0.56 m, A = R/a = 1.8, B0=3.2 T, Q=1) is the next-generation high-temperature superconducting (HTS) spherical tokamak (ST) designed by Shannxi Startorus Fusion Technology Co., Ltd., a commercial fusion enterprise from China. The spherical tokamak is an economical and fast-building option for a fusion reactor, which allows to confine high-pressure plasma using a modest magnetic filed in a compact device due to its low aspect ratio. However, the limited space in the center column of the ST, also due to the low aspect ratio, necessitates higher engineering current density and reduced radiation protection for the magnet used in the ST. Attracted by the high current-carrying capacity and greater temperature margin of the HTS technology, researches on HTS toroidal field model coil (TFMC) and central solenoid model coil (CSMC) are conducted by Startorus Fusion.
The TFMC is one of sixteen REBCO toroidal field coils with 4 meter in height, achieving 6.87 T peak filed-on-coil with 4.4 kA of terminal current. The engineering current density of the winding pancake is 147 A/mm2 while the entire magnet, including the structural case, is 62 A/mm2. The TFMC consists of two double no-insulation pancakes, each with 104 turns. The winding pancake is co-wound by 9 superconducting tapes and 1 stainless steel tape, all 12 mm in width. The ground insulation of the TFMC is achieved by filling the epoxy-impregnated G-10 panels between the structural case and winding pancakes. A specially designed demountable pancake-to-pancake joint for the 9-layer stacked cable can operates in the 0.2 to 1 nΩ range at 20 K. An innovative technique involving the application of Stycast 2850 on the side of no-insulation pancake for efficient insulation and cooling has been proposed.
The CSMC is a 1/10 scaled-down REBCO central solenoid coil with 0.4 meter in height, 160 mm in inner radius and 240 mm in outer radius. It achieves 13.8 T peak filed-on-coil with 7.2 kA of terminal current. The CSMC provides a magnetic flux of 1.5 Wb and a maximum magnetic field change rate of 70 T/s, generating 8 V loop voltage for plasma breaking. The engineering current density of the winding pancake is 202 A/mm2 while the entire magnet, including the structural case, is 100 A/mm2. It consists of 26 double pancakes, each with 28 turns, using a non-twisted stacked superconducting cable. This cable is co-wound by 36 superconducting tapes with 6 mm in width. The turn-to-turn insulation of the CSMC is achieved by wrapping the cable in glass-Kapton tapes with a thickness of 0.5 mm. Additionally, the ground insulation of the CSMC is provided by epoxy-impregnation of the entire magnet.
Both the TFMC and CSMC are cooled down by a crycooler based cryogenic system provided 300 W of cooling power at 20 K with mass flow rate of supercritical helium up to 18.4 g/s at a maximum design pressure of 5 bar. The manufacturing of TFMC and CSMS is currently in progress, with the cooling, discharge, and AC loss test results of the CSMC expected by mid-2025, and the cooling and charging test results of the TFMC expected by late 2025.
