Optically Multiplexed Neutron Time-of-Flight Technique for ion Temperature Imaging in Inertial Confinement Fusion

Modern experiments in laser-driven inertial confinement fusion (ICF) are susceptible to contamination of the central hotspot by high-Z material during compression that impedes thermonuclear burn. Hotspot mix can be quantified using the ion temperature distribution of the implosion given the predicted deviation between the plasma and contaminant1. but current neutron time-of-flight (nToF) diagnostics can 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 a spatially resolved temperature measurement on a single photomultiplier tube (PMT). A prototype detector was constructed in which 20 optical fibers of increasing length were coupled to an EJ-262 plastic scintillator at one end and a Photek PMT210 at the other. The detector was tested on the OMEGA laser and an nToF pulse was successfully measured through all 20 channels at the expected time separations, though direct interactions of fusion products with the PMT interfered with the first 5 channels. Design methodology, material selection, experimental results, and preliminary data analysis are discussed. Next steps will be aimed at applying this technique to previous work demonstrating a 1D spatially resolved ion temperature imager on OMEGA
²
,3 to evaluate the feasibility of 2D ion temperature imaging at NIF with a cost-efficient detector.