Optically multiplexed neutron time-of-flight technique for ion temperature imaging in inertial confinement fusion*

Laser-driven inertial confinement fusion experiments are susceptible to contamination of the hotspot by high-Z material during compression that impedes thermonuclear burn. This mix can be quantified using the ion temperature distribution of the implosion given the predicted deviation of the contaminant, but current neutron time-of-flight (nTOF) diagnostics only measure the spatially integrated temperature. This project probes the feasibility of using time multiplexed optical fibers to record nTOF spectra from segmented thin scintillators, which could be used to collect spatially resolved ion temperature measurements with a single photomultiplier tube (PMT). A prototype detector was constructed using 20 multiplexed fiber channels coupled to a monolithic EJ-262 plastic scintillator and a Photek PMT210. nTOF pulses were successfully measured through all channels at the expected time separations on experiments at the OMEGA laser. Design methodology, material selection, experimental results, and data analysis are discussed. Next steps are now aimed at applying this technique to previous work demonstrating a 1D spatially resolved ion temperature imager on OMEGA in order to demonstrate quasi-2D ion temperature imaging at NIF with a cost-efficient detector.