Latest Progress in the Characterization of Neutron Flux Monitors for the SPARC Tokamak

In the SPARC tokamak, neutron flux monitors (NFM) will measure real-time neutron flux in the tokamak hall and convert the measurement to fusion power via calibration. Such measurements are of great importance for demonstrating fusion power breakeven, machine protection, and plasma operations. To cover the wide dynamic range of SPARC scenarios, from ~1E8 n/s calibration range to >1E19 n/s primary reference discharge (PRD), multiple types of NFMs are proposed. This poster presents the latest results of characterization of a BF3-filled proportional counter (PC) and a U238 fission chamber (FC). The BF3 PC is a highly sensitive detector for the calibration range. As it is a thermal neutron detector intrinsically, high density polyethylene (HDPE) will be used to moderate fast neutrons locally. The U238 FC, an overall low-sensitivity detector and insensitive to neutrons < 1 MeV, is for operational plasma scenarios. The U238 PC is equipped with a borated polyethylene (B-PE) box with an opening channel to filter out scattered neutrons from the surrounding environment so as to prioritize direct neutrons. Experiments are performed to characterize these detectors' linearity, neutrons vs gamma discrimination capability, sensitivity to DT and DD neutrons, neutron moderators and shields design, effects of magnetic fields, and different electronics chains. OpenMC is used to simulate both the experiments and the detectors' performance in SPARC. The FC shows great count rate response linearity to both DT and DD neutrons and insensitivity to gammas. The BF3 PC shows great linearity to DT neutrons, low sensitivity to gammas, and the HDPE moderator improved signals effectively. More results on effects of magnetic fields, alternative electronics, and the PC's performance to DD neutrons will be presented.