Current plans call for a system of current mode neutron detectors for the National Ignition Facility for extending the range of neutron yields below that of the neutron activation system, for ion-temperature measurements over a wide yield range, and for determining the average neutron emission time. The system will need to operate over a yield range of 106 for the lowest-yield experiments to 1019 for high-yield ignited targets. The requirements will be satisfied using several detectors located at different distances from the target. This article presents a conceptual design for the NIF nToF system.

A review of recent progress on the design of a diagnostic system proposed for ignition target experiments on the National Ignition Facility (NIF) will be presented. This diagnostic package contains an extensive suite of optical, x ray, gamma ray, and neutron diagnostics that enable measurements of the performance of both direct and indirect driven NIF targets. The philosophy used in designing all of the diagnostics in the set has emphasized redundant and independent measurement of fundamental physical quantities relevant to the operation of the NIF target. A unique feature of these diagnostics is that they are being designed to be capable of operating in the high radiation, electromagnetic pulse, and debris backgrounds expected on the NIF facility. The diagnostic system proposed can be categorized into three broad areas: laser characterization, hohlraum characterization, and capsule performance diagnostics. The operating principles of a representative instrument from each class of diagnostic employed in this package will be summarized and illustrated with data obtained in recent prototype diagnostic tests.

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The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements.

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.