[en] This report investigates the use of x-rays and electrons to excite a CVD polycrystalline diamond detector during a double pulse experiment to levels corresponding to those expected during a successful (1D clean burn) and a typical failed ignition (2D fizzle) shot at the National Ignition Facility, NIF. The monitoring of a failed ignition shot is the main goal of the diagnostic, but nevertheless, the study of a successful ignition shot is also important. A first large neutron pulse is followed by a smaller pulse (a factor of 1000 smaller in intensity) after 50 to 300 ns. The charge carrier densities produced during a successful and failed ignition shot are about 10¹⁵ e-h+/cm³ and 2.6* 10¹² e-h+/cm³ respectively, which is lower than the 10¹⁶ e-h+/cm³ needed to saturate the diamond wafer due to charge recombination. The charge carrier density and the signal induced in the diamond detector are calculated as a function of the incident x-ray and electron energy, flux, and detector dimensions. For available thicknesses of polycrystalline CVD diamond detectors (250 (micro)m to 1000 (micro)m), a flux of over 10¹¹ x-rays/cm² (with x-ray energies varying from 6 keV to about 10 keV) or 10⁹ β/cm² (corresponding to 400 pC per electron pulse, E_β > 800 keV) is necessary to excite the detector to sufficient levels to simulate a successful ignition's 14 MeV peak. Failed ignition levels would require lower fluxes, over 10⁸ x-rays/cm² (6 to 10 keV) or 10⁶ β/cm² (1 pC per electron pulse, E_β > 800 keV). The incident pulse must be delivered on the detector surface in several nanoseconds. The second pulse requires fluxes down by a factor of 1000. Several possible x-ray beam facilities are investigated: (1) the LBNL Advanced Light Source, (2) the Stanford SLAC and SPEAR, (3) the BNL National Synchrotron Light Source, (4) the ANL Advanced Photon Source, (5) the LLNL Janus laser facility. None of the cyclotrons/synchrotrons (1) through (4) are bright enough. The maximum monoenergetic x-ray flux available at the energies of interest (6-10 keV) is about 10⁴ x-rays/ns/cm² at 10 m from the source. The maximum white beam x-ray flux (thus all energies of x-rays are used) is about 10⁶ x-rays/ns/cm² at 10 m from the source. These numbers are well below the necessary 10¹¹ x-rays/cm² produced in a few ns. Also, producing double pulses separated from 50 to 300 ns with a factor of 1000 contrast between the first and second pulses seems very challenging using a cyclotron/synchrotron. The Janus laser-based x-ray facility (5) can generate over 10¹¹ x-rays/cm² at 10 cm from the target (nickel or zinc target, 7.5 keV to 8.6 keV x-rays lines) and double pulses are possible. Electron beams at the linac facility at LLNL can deliver from 5 to 100 pC double pulses, with electron energies varying from 15 to 90 MeV. Use of a 5 pC pulse could achieve the failed ignition densities, and a 100 pC pulse is just short of satisfying the densities of a successful ignition shot. Other linacs with higher current (400 pC per shot would be necessary) could satisfy both ignition densities

[en] X-ray imaging will be an important diagnostic tool for inertial confinement fusion (ICF) research at the National Ignition Facility (NIF). However, high neutron yields will make x-ray imaging much more difficult than it is at current smaller facilities. We analyze the feasibility and performance of an Ignition X-Ray Imager to be used on cryogenic DT implosions at NIF. The system is intended to provide time-integrated, broadband, moderate-energy x-ray core images of imploding ICF capsules. Highly magnified, spectrally-filtered images created using an array of pinholes placed close to the target will be projected onto a scintillator placed at the target chamber wall. A telescope will be used to relay the scintillator emission to a distant optical detector that is time-gated in order to minimize backgrounds, in particular from neutrons. The system is optimized with respect to spatial-resolution, signal-to-background and signal-to-noise ratios

[en] Refraction enhanced x-ray phase contrast imaging is crucial for characterization of deuterium-tritium (DT) ice layer roughness in optically opaque inertial confinement fusion capsules. To observe the time development of DT ice roughness over ∼ second timescales, we need a bright x-ray source that can produce an image faster than the evolution of the ice surface roughness. A laser produced plasma x-ray source is one of the candidates that can meet this requirement. We performed experiments at the Janus laser facility at Lawrence Livermore National Laboratory and assessed the characteristics of the laser produced plasma x-ray source as a potential backlight for in situ target characterization

[en] We report the first neutron data for a single crystal Chemical Vapor Deposition (CVD) diamond sensor. Results are presented for 2.5, 14.1, and 14.9 MeV incident neutrons. We show that the energy resolution for 14.1 MeV neutrons is at least 2.9% (as limited by the energy spread of the incident neutrons), and perhaps as good as 0.4% (as extrapolated from high resolution α particle data). This result could be relevant to fusion neutron spectroscopy at machines like the International Thermonuclear Experimental Reactor (ITER). We also show that our sensor has a high neutron linear attenuation coefficient, due to the high atomic density of diamond, and this could lead to applications in fission neutron detection

[en] We are studying the response of a CVD diamond detector to a strong x-ray pulse followed by a second weaker pulse arriving 50 to 300 ns later, with a contrast in amplitude of about 1000. These tests, performed at the LLNL Jupiter laser facility, are intended to produce charge carrier densities similar to those expected during a DT implosion at NIF, where a large 14.1 MeV neutron pulse is followed by a weak downscattered neutron signal produced by slower 6-10 MeV neutrons. The number of downscattered neutrons must be carefully measured in order to obtain an accurate value for the areal density, which is proportional to the ratio of downscattered to primary neutrons. The effects of the first strong pulse may include saturation of the diamond wafer, saturation of the oscilloscope, or saturation of the associated power and data acquisition electronics. We are presenting a double pulse experiment that will use a system of several polycrystalline CVD diamond detectors irradiated by 8.6 keV x-rays emitted from a zinc target. We will discuss implication for a NIF areal density measurement

[en] Ignition targets for the National Ignition Facility (NIF) will contain a cryogenically cooled ∼ 75 (micro)m-thick deuterium/tritium (DT) ice layer surrounded by a ∼ 150 (micro)m-thick beryllium (Be) shell [1]. Ignition target design optimization depends sensitively on the achievable inner surface quality of the ice layer and on the pressure of the DT gas inside the ice, which is determined by the temperature of the ice. The inner ice layer surface is smoothest at temperatures just below the DT ice/liquid/gas triple point (3T), but current ignition target designs require central gas pressures of 0.3 mg/cm3, corresponding to an ice layer temperature 1.5 K below the triple point (3T-1.5). At these lower temperatures, the ice layer quality degrades due to the formation of cracks and other features

[en] X-ray imaging is a fundamental diagnostic tool for inertial confinement fusion (ICF) research, and provides data on the size and the shape of the core in implosions. We report on the feasibility and performance analysis of an ignition x-ray imager to be used on cryogenic DT implosions at the National Ignition Facility. The system is intended to provide time-integrated, broadband, moderate-energy x-ray core images of imploding ICF capsules. It is optimized with respect to spatial-resolution, signal-to-background and signal-to-noise ratios, taking into account the extreme operating conditions expected at NIF due to high expected neutrons yields, gamma-rays, and x-rays from laser-plasma interactions

[en] A 5 x 0.25 mm Chemical Vapor Deposited (CVD) diamond detector, with a voltage bias of + 250V, was excited by a 400 nm laser (3.1 eV photons) in order to study the saturation of the wafer and its associated electronics. In a first experiment, the laser beam energy was increased from a few tens of a pJ to about 100 (micro)J, and the signal from the diamond was recorded until full saturation of the detection system was achieved. Clear saturation of the detection system was observed at about 40 V, which corresponds with the expected saturation at 10% of the applied bias (250V). The results indicate that the interaction mechanism of the 3.1 eV photons in the diamond (E_bandgap = 5.45 eV) is not a multi-photon process but is linked to the impurities and defects of the crystal. In a second experiment, the detector was irradiated by a saturating first laser pulse and then by a delayed laser pulse of equal or smaller amplitude with delays of 5, 10, and 20 ns. The results suggest that the diamond and associated electronics recover within 10 to 20 ns after a strong saturating pulse

[en] Current designs for inertial confinement fusion capsules for the National Ignition Facility (NIF) consist of a solid deuterium-tritium (D-T) fuel layer inside of a copper doped beryllium capsule. Phase contrast enhanced x-ray imaging is shown to render the D-T layer visible inside the Be(Cu) capsule. Phase contrast imaging is experimentally demonstrated for several surrogate capsules and validates computational models. Polyimide and low density divinyl benzene foam capsules were imaged at the Advanced Photon Source synchrotron. The surrogates demonstrate that phase contrast enhanced imaging provides a method to characterize surfaces when absorption imaging cannot be used. Our computational models demonstrate that a rough surface can be accurately reproduced in phase contrast enhanced x-ray images

[en] Two static x-ray imagers (SXI) will be used to monitor beam pointing on all target shots in the National Ignition Facility. These pinhole-based instruments will provide time integrated two-dimensional images of target x-ray emissions in the energy range between 2 and 3 keV. These instruments are not DIM based and will view along dedicated lines of sight from near the top and bottom ports of the target chamber. Beams that miss or clip the hohlraum laser-entrance holes will produce x-ray emission on the ends of the hohlraum, indicating improper beam pointing and/or target positioning. The SXIs will also be used to quantify beam focusing and pointing by producing x-ray images of dedicated test targets irradiated by focused beams at precalculated positions. A proposed design is presented, along with supporting data from NOVA target experiments