Diagnosing inertial confinement fusion gamma ray physics (invited).

The gamma reaction history (GRH) diagnostic is a multichannel, time-resolved, energy-thresholded γ-ray spectrometer that provides a high-bandwidth, direct-measurement of fusion reaction history in inertial confinement fusion implosion experiments. 16.75 MeV deuterium+tritium (DT) fusion γ-rays, with a branching ratio of the order of 10(-5)γ/(14 MeV n), are detected to determine fundamental burn parameters, such as nuclear bang time and burn width, critical to achieving ignition at the National Ignition Facility. During the tritium/hydrogen/deuterium ignition tuning campaign, an additional γ-ray line at 19.8 MeV, produced by hydrogen+tritium fusion with a branching ratio of unity, will increase the available γ-ray signal and may allow measurement of reacting fuel composition or ion temperature. Ablator areal density measurements with the GRH are also made possible by detection of 4.43 MeV γ-rays produced by inelastic scatter of DT fusion neutrons on (12)C nuclei in the ablating plastic capsule material.

Using x-rays to test chemical vapor deposited diamond detectors for areal density measurement at the National Ignition Facility.

At the National Ignition Facility (NIF), 192 laser beams will compress a target containing a mixture of deuterium and tritium that will release fusion neutrons, photons, and other radiation. Diagnostics are being designed to measure this emitted radiation to infer crucial parameters of an ignition shot. Chemical vapor deposited (CVD) diamond is one of the ignition diagnostics that will be used as a neutron time-of-flight detector for measuring primary (14.1 MeV) neutron yield, ion temperature, and plasma areal density. This last quantity is the subject of this study and is inferred from the number of downscattered neutrons arriving late in time, divided by the number of primary neutrons. We determine in this study the accuracy with which this detector can measure areal density when the limiting factor is detector and electronics saturation. We used laser-produced x-rays to reproduce NIF signals in terms of charge carrier density, time between pulses, and amplitude contrast and found that the effect of the large pulse on the small pulse is at most 8.4%, which is less than the NIF accuracy requirement of +/-10%.

Tests and calibration of NIF neutron time of flight detectors.

The National Ignition Facility (NIF) neutron time of flight (NTOF) diagnostic will measure neutron yield and ion temperature in all NIF campaigns in DD, DT, and THD(*) implosions. The NIF NTOF diagnostic is designed to measure neutron yield from 1x10(9) to 2x10(19). The NTOF consists of several detectors of varying sensitivity located on the NIF at about 5 and 20 m from the target. Production, testing, and calibration of the NIF NTOF detectors have begun at the Laboratory for Laser Energetics (LLE). Operational tests of the NTOF detectors were performed on several facilities including the OMEGA laser at LLE and the Titan laser at Lawrence Livermore National Laboratory. Neutron calibrations were carried out on the OMEGA laser. Results of the NTOF detector tests and calibration will be presented.