Fusion γ Ray Signals from ICF Targets Recorded with Streak Camera

Summary form only given. For a dozen years, the fusion reaction rate in inertial confinement fusion (ICF) capsules has been determined by monitoring the production rate of fusion neutrons. Future high-yield targets producing >10¹⁵ neutrons should allow reaction rates to be measured with γ rays produced in deuterium-tritium (DT) fusion. Using γ rays makes the measurement independent of target-to-detector distance, but the low branching ratio for γ-ray production (<10^-4) makes the task difficult at current ICF facilities where shot yields are <10¹⁴ neutrons. Two detector systems based on Cherenkov gas cells have been tested at the OMEGA laser facility. Incident γ rays produce forward-directed, relativistic electrons in a converter foil at the entrances to high-pressure (up to 100 psi) gas cells containing CO₂ gas. The electrons generate Cherenkov light when they travel faster than the speed of light through the CO₂ gas. Reflective optics collects the light at the output of each cell. For one system the signal is recorded with a fast photomultiplier tube (PMT) at the output of the gas cell. The other system uses relay optics to transfer the Cherenkov light to a streak camera several meters away. The PMT work has been presented in an earlier paper. This paper describes the streak camera based detector system and initial measurements made with it