Neutron penumbral imaging of inertial confinement fusion targets

Abstract

The first 14-MeV neutron images of imploded microballoons have been obtained on the Phébus laser facility at CEL-V. The sizes of the source have been measured, in direct-drive experiments, by means of a coded-aperture imaging system. The principle is to use a thick aperture with a diameter larger than that of the source to image the microballoon. The deconvolution of the recorded image allows one to reconstruct the image of the neutron source, and this technique allows one to obtain images at a lower neutron yield than with a conventional pinhole camera. The choice of the experimental conditions is a trade-off between the Phébus conditions, the spatial resolution, and the image reconstruction method that is related to the signalto-noise ratio. The sensitivity of the diagnostic is strongly dependent on the number of scintillator photons that are collected by the recording system. The neutron measurement threshold of our experimental setup is typically 2 × 10¹⁰ neutrons/shot for neutron source sizes of 800 μm.