Startup and Quench Electromagnetic Simulation of a Bitter Plate TF Coil Concept For the Fusion Nuclear Science Facility (FNSF)

Current distributions during startup and quench of very large reactor relevant coil systems will vary significantly from the smaller prototype magnets. A reactor scale simulation is needed. In this study, the FNSF magnet from the 2017 study is used as an example of a full sized reactor. The intent of the study is to investigate use of HTS conductors in the FNSF and how sizing and performance might be affected. A pancake or Bitter magnet like winding pattern is investigated to allow inductive and resistive redistribution of currents. A portion of the winding pack retains some resistivity to aid in redistribution of current during a transient or quench. Resistive materials can be used to support energy absorption for stability or to provide partial current dump capability during a quench, however, the primary quench mitigation mechanism is inductive redistribution of currents around the quench zone. In this implementation, the Bitter plate is both structural - similar to radial plates in ITER and electrical, intended, to limit current concentration during ramp-up. Use of localized resistors and parallel current paths are used to encourage more uniform startup currents. The analysis is a transient electromagnetic simulation using ANSYS. It is a cyclic symmetry modeling of an individual plate and is limited by the assumption that a local quench is repeated by the cyclic symmetry. This is a concession to the model size. Results are discussed in the context of performance needed for the FNSF.