Designing a Noble Gas Excimer Neutron Diagnostic for CMFX with GEANT4

The Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland, College Park is slated to run with a deuterium plasma during the last stage of its operating plan. It is expected to produce approximately 10⁷ - 10⁸ D-D (2.45 MeV) fusion neutrons per discharge. The coaxial solenoidal magnets of the experiment produce a substantial stray magnetic field over the area surrounding the experiment, making traditional neutron detectors like Helium-3 tubes impractical. With input from the NASA PICASSO supported DOWSER project, we explore the use of a noble-gas-excimer-based neutron detector technology for measuring D-D fusion neutrons and building spatial neutron diagnostics. GEANT4 was used to simulate a series of detector and moderator configurations and evaluate their angular sensitivity to incident neutrons, as well as a source with the geometry of CMFX. The performance of an axial array of modular square detectors with 7.5cm thick polyethylene block moderators is evaluated.