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Coded Aperture Imaging of Nuclear Fusion

Fri., Oct. 18, 2019 3:30 p.m. - Fri., Oct. 18, 2019 4:30 p.m.

Location: LB 235

Abstract: The Coded Aperture Imaging (CAI) technique has been used to image the deuterium-deuterium (D-D) fusion source in the NX2 dense plasma focus (DPF) device, using protons emitted from the D(d,p)T reaction. CAI is a form of multiplexed pinhole imaging which uses many small pinholes arranged in specific patterns so as to obtain images with the good spatial resolution expected for a small pinhole, together with high brightness and signal-to-noise ratio (SNR) associated with a much larger open aperture. Our theoretical study of CAI led us to the conclusion that for extended sources, such as the PF pinch, coded mask patterns of relatively low open fraction (i.e. significantly less than 50%) are optimal. Therefore the mask patterns used in our experimental work are based on Singer cyclic difference sets. Monte Carlo simulations of CAI and pinhole imaging were performed in order to validate our theoretical SNR formulae and test our decoding algorithm. CR-39 polymer nuclear track detectors were used to register the ~3 MeV protons emitted from the PF pinch. As an additional test of the CR-39 detector scanning procedures, theoretical formulae, and CAI decoding algorithm, various source shapes were simulated experimentally using a 226Ra alpha particle source. Significantly, this work represents the first application of the CAI technique to imaging the fusion source in a plasma focus device.