Modeling a one-dimensional bremsstrahlung and neutron imaging array for use on Sandia's Z machine

Inertial confinement fusion is being studied on the Z facility at Sandia Na tional Laboratories. Z is a large z-pinch machine which can provide 20 MA o f current to z-pinch loads producing similar to 1.8 MJ of soft x rays in le ss than 10 ns. Within the pinch region, decelerated electrons produce a str ong source of bremsstrahlung radiation which varies from shot to shot. Addi tionally, a variety of inertial confinement fusion targets may produce fusi on neutrons, the intensity and distribution of which depend on the temperat ure and density of the pinch. In this article, we describe the computer mod eling behind the shielding design of a simple time-resolved, one-dimensiona l imaging array. This diagnostic will provide a time history for both the b remsstrahlung and neutron production as a function of height in the target. Calculations show that by building an array of scintillator fibers separat ed by long, thin tungsten collimator plates, a sampling rate of 0.254 mm at the target can be achieved. The corresponding channel-to-channel discrimin ation for such a design is shown to be better than 1000::1 for <4 MeV photo ns and 100::1 for 2.45 MeV neutrons. By coupling scintillator fibers to a f iber-optic streak camera system, the system time response is expected to be dominated by the scintillator response (similar to 1.2 ns). (C) 1999 Ameri can Institute of Physics. [S0034-6748(99)55101-0].