Preliminary result of Coded Aperture Imaging on NX2 Plasma Focus

Abstract

Summary form only given. The Coded Aperture Imaging (CAI) technique is used to study the spatial distribution of fusion reactions in a 3 kJ Plasma Focus device operated in its neutron-optimized regime (11 kV and 14 mbar D2 gas). A coded mask (8times8 mm2, 20times20 pixel) was fabricated in a high strength alloy using micro- electro- discharge machining. The mask pattern, based on a Singer set, has 57 open circular holes representing 6.3% open area. The nuclear track detector material CR-39 was employed to register the ~3 MeV fusion protons from the D(d,p)T reaction. A 50 mum kapton film covering the CR-39 stopped all energetic charged particles other than the fusion protons. The CAI camera was positioned at 55deg to the plasma focus axis, with anode-to-mask distance of 33 mm, and mask-to-detector distance of 35 mm. An indium-foil activation detector was employed simultaneously to measure the neutron yield for each PF shot. Following chemical etching of the CR-39 detectors the area, circularity, mean optical density and (x,y) positions of the proton tracks were measured by an automated scanning system. A deconvolution algorithm was applied to the (x,y) data for recognized proton tracks to obtain images of the PF fusion source. A simple pinhole camera was used simultaneously with the CAI camera in order to study the relative SNR (Signal to Noise Ratio). The obtained images confirm the superior SNR characteristics of the CAI camera. We also report the results of numerical Monte Carlo simulations carried out to study the performance of the CAI imaging system, and experimental simulations using a Radium-226 alpha source with brass stencils of varying shapes. The results demonstrate that the CAI system can achieve the resolution and SNR requirements necessary for imaging the fusion proton source.