Showing papers by "T. W. Phillips published in 2005"

Characterization of a picosecond laser generated 4.5 keV Ti K-alpha source for pulsed radiography

Abstract: Kα radiation generated by interaction of an ultrashort (1ps) laser with thin (25μm) Ti foils at high intensity (2×1016W∕cm2) is analyzed using data from a spherical Bragg crystal imager and a single hit charge-coupled device spectrometer together with Monte Carlo simulations of Kα brightness. Laser to Kα and electron conversion efficiencies have been determined. We have also measured an effective crystal reflectivity of 3.75±2%. Comparison of imager data with data from the relatively broadband single hit spectrometer has revealed a reduction in crystal collection efficiency for high Kα yield. This is attributed to a shift in the K-shell spectrum due to Ti ionization.

Progress with CVD Diamond Detectors for ICF Neutron Time-of-Flight Applications

Abstract: Summary form only given. Synthetic polycrystalline diamonds produced by chemical vapor deposition (CVD) are the leading candidates for neutron time-of-flight detectors at the National Ignition Facility (NIF). The detectors based on CVD diamonds are fast and radiation hard. In the last year, significant progress was made on the 60-beam OMEGA laser system in the development of CVD diamond detectors for inertial confinement fusion (ICF) applications. Sensitivity and time response were measured on DT and DD implosions for CVD diamonds of different sizes and at different bias voltages. Characteristics of a CVD diamond detector hardened with a fluence of 1016 neutrons/cm2 were also measured. Several different housings for the CVD diamonds were developed. The sensitivity of the CVD diamond detectors to hard X-rays, gamma rays and EMP noise was studied. Two CVD diamond detectors are now permanently installed on OMEGA and are used as neutron time-of-flight detectors for yield and ion temperature measurements in high-yield implosions. The implementation of the CVD diamond detectors on the NIF will be discussed.

Study of Scattered Background Neutron in NIF and Time-of Flight (TOF) to Measure Neutron

Abstract: Some of the planned core diagnostics for National Ignition Facility (NIF) will use neutron time-of-flight (TOF) spectroscopy techniques to gather information for primary neutron yield measurement or neutron imaging. This technique has been widely and routinely used at other laser facilities including Nova and Omega. TOF methods will also be used to observe target fuel areal density (radial integral of density) via measuring the number of primary 14.1 MeV neutrons that are down-scattered to lower energies by nuclear collisions inside the compressed target core. The substantially larger target chamber size and higher neutron yield for NIF raises issues related to the large number of scattered neutrons produced by high yield deuterium-tritium (D-T) shots at NIF. The effect of primary neutrons scattered by the walls of the massive target chamber and structures both inside and outside the chamber will contribute a significant scattered background signal when trying to determine the number of neutrons down-scattered from the target core. The optimum detector locations outside the target chamber or target bay wall will be proposed. Appropriate collimators at the chamber port and the bay wall (between the neutron source at target chamber center (TCC) and detector) that maximize detection of signal neutrons while minimizing the background from scattered neutrons and neutron induced gamma rays will also be presented.