Neutronics Design of Calibration Range Neutron Flux Monitors in SPARC*

This poster presents the design of calibration-range neutron flux monitors (NFM) for the SPARC tokamak from a neutronics perspective. NFMs measure the real-time neutron yield rates, which give fusion power via calibration. Calibration is a process in which the relationship between neutron source intensity and NFM response is experimentally measured, by employing an in-situ neutron source with well-known emission characteristics. Boron-10-lined ionization chambers (ICs) and Uranium-238 fission chambers are planned for SPARC's operation range (1E15 - 5E19 n/s), but they are not sensitive enough to detect calibration sources (<1E10 n/s). Thus, additional high-sensitivity NFMs for calibration are proposed: B10-lined proportional counters (PCs) and Boron Trifluoride (BF3) gas-filled PCs. Borated high-density polyethylene (HDPE) and HDPE shieldings will be used to prioritize direct neutrons and tune the PCs' sensitivities to fast neutrons. The PCs should be as sensitive as possible while having dynamic ranges overlap with the B10 ICs. The PCs' responses are simulated by a constructive solid geometry-based OpenMC SPARC model. Representing the DT generator and Californium-252 sources, isotropic point neutron sources of corresponding energy spectra are placed at different locations in the tokamak vessel. A cross-verification plasma source of 1E14 n/s, within the overlap of the PCs' and the ICs' dynamic ranges, will also be simulated.