Experimental Assessment and Model Validation of the SPARC Toroidal Field Model Coil

Abstract

The SPARC Toroidal Field Model Coil (TFMC) experimental tests are described. The tests include detailed comparisons to a hierarchy of electromagnetic and structural models of the coil. The tests confirmed the ability of the no-insulation notwist (NINT) configuration to provide highly stable DC operations with peak magnetic field in excess of 20 tesla at the REBCO tape stacks. The advantages of the modular TFMC approach were validated including the ability to test and probe the REBCO and structural response of the coil in stages; a strategy that will be applied to large-scale coil production for SPARC. The electromagnetic models showed high fidelity agreement to the DC and charging coil performance in terms of current distribution, voltages and heating. The transient response of the TFMC to open-circuit events was examined. The coil exhibited the positive features of the NINT design with very low induced voltages and a predictable redistribution of current and resulting volumetric heating. However, highly localized damage occurred during a programmed open-circuit at operational conditions similar to those used in the SPARC tokamak, in agreement with calibrated electromagnetic models. This revealed the cause and remedy to the thermal instability that gives rise to the damage. Therefore, the conclusion of the tests is that the NINT TFMC was confirmed as meeting the programmatic requirements for SPARC and, more generally, for high field tokamaks.

Performance of demountable solder joints for no-insulation superconducting coils produced by vacuum pressure impregnation

“…To infer this effect from a different experiment, the joint resistance can be analyzed from the recent SPARC TFMC, built and tested to high current and high field at the PSFC. A series of papers have been published on the experimental and modeling results from the TFMC campaign [22,23]. This coil was operated at 20 K and had indium compression joints between no-insulation pancakes.…”

Performance test of REBCO CICC sub-cables with l0 kA current under 20 T background field

“…Following the successful achievements of pancake winding made by high temperature superconductors (HTS) rare-earth barium copper oxide (REBCO) tapes as small insert solenoids, the fusion magnet community is engaged in the past decade in an effort to develop high current conductors based on REBCO tapes to wind large high field magnets [1,2].…”

“…The test reported in [3], at 20 T background field and up to 10 kA is to my knowledge a world record for HTS cables with this layout. Only the SPARC Model Coil [2] has a larger combination of operating field and current, but it is based on a different technology, 'non-insulated, soldered stacks of tapes'.…”

Building the Runway: A New Superconducting Magnet Test Facility Made for the SPARC Toroidal Field Model Coil

“…This section is meant to summarize the overall system architecture, design specifications, and system interfaces. A detailed accounting of the helium circuit is provided in the article by Michael et al in this series [8], and of the cooling of the current leads in Fry et al [9], with measurements from operation appearing in Whyte et al [10].…”

“…In the following, the I&C system is summarized, noting that more detailed information on particular sensors and associated equipment is provided in the subsystem articles pertaining to the coil (Vieira et al [14]) and its operation (Whyte et al 1 The advice of the manufacturer was that the cryocooler arrays should be placed in a field ≤ 5 mT (50 G); additional margin was added, allowing future operation of magnets with greater fringe fields than the TFMC. [10]), as well as the helium circuit (Michael et al [8]), and current leads (Fry et al [9]).…”