NEUTRON PENUMBRAL IMAGING OF INERTIAL CONFINEMENT FUSION-TARGETS

The first 14-MeV neutron images of imploded microballoons have been ob tained on the Phebus laser facility at CEL-V. The sizes of the source have been measured, in direct-drive experiments, by means of a coded-a perture imaging system. The principle is to use a thick aperture with a diameter larger than that of the source to image the microballoon. T he deconvolution of the recorded image allows one to reconstruct the i mage of the neutron source, and this technique allows one to obtain im ages at a lower neutron yield than with a conventional pinhole camera. The choice of the experimental conditions is a trade-off between the Phebus conditions, the spatial resolution, and the image reconstructio n method that is related to the signal-to-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 measu rement threshold of our experimental setup is typically 2 x 10(10) neu trons/shot for neutron source sizes of 800 mu m.