Gamma-ray-based fusion burn measurements

Abstract

A gas Cerenkov detector with a 12-MeV threshold for gamma-ray detection has been built for use on the OMEGA laser system to record high-energy gamma rays emitted during DT gas burn. Recording the 16.7-MeV gamma ray while discriminating against the lower energy 14-MeV neutron-induced gammas is an important objective using this detector system. Detector design, sensitivity, and background studies were possible using the Integrated Tiger Series Monte Carlo code modified to include Cerenkov production and full time-history of all particles. The results of this code were iterated with the ASAP optics code to optimize the light collection system, while providing the radiation shielding and stray light baffles to minimize backgrounds. As an initial test of the instrument, 8-20 MeV electrons from the Idaho State University linear accelerator were used in lieu of gamma rays. The primary results of these tests are that electron-produced Cerenkov has been observed and the Cerenkov threshold curve established for this instrument.

Remarks on detecting high-energy deuterium–tritium fusion gamma rays using a gas Cherenkov detector

“…Energy thresholding was used to discriminate between the 16.75 MeV gamma rays and assorted neutron-induced inelastic gamma rays. Experimental validation of the threshold properties was accomplished using a pulsed LINAC electron-beam; these results compared within expectations to Monte Carlo predictions (Berggren et al, 2001). Such experiments also revealed the existence and negligibly low levels below threshold of both fluorescence and OTR.…”

“…4. This instrument is the product of a process that optimized Cherenkov photon production, collection efficiency, and response time, while minimizing the effects of undesirable secondary radiation sources (Berggren, 2001). The essentials are a 1.5-cm thick beryllium (or aluminum) converter, cylindrical CO 2 gas chamber, and optical collection system.…”

A new method for high-energy pulsed Gamma measurement within intense background x-rays

“…Function q ′ almost always equals one. For 6.13 MeV Gamma, formula (3) could be rewritten as formula (4).…”

“…As the energy of background Gamma (or x-rays) is much lower than that of the aimed Gamma, threshold Gamma detectors which are only sensitive to some specified energy range are required. Los Alamos National Laboratory (LANL), Lawrence Livermore Na-tional Laboratory (LLNL) and Chinese Academy of Engineering Physics (CAEP) have developed diagnostic systems [4,5] for the measurement of the reaction time history of the D-T burn. Such systems have provided a high signal-to-noise ratio (about 10 5 − 10 6 ).…”

Design and performance study of a gas-Cherenkov detector with an off-axis parabolic reflector for inertial confinement fusion experiments

“…GCD can detect high-energy fusion gamma rays while remaining insensitive to neutrons and lowenergy neutron-induced gamma rays. Two Cherenkov detectors, the compact GCD and the multi-channel gamma reaction history (GRH), have been developed by Berggren et al [14], Malone et al [15] and Herrmann et al [16,17] for measuring multiple-energy gamma-rays produced during DT implosions at the National Ignition Facility (NIF). The compact GCD used two parabolic reflectors to collect the Cherenkov photons, and a centered tungsten shielding to prevent DT gamma rays from entering the high-speed photon detector directly.…”