Particle Splitting for Monte-Carlo Simulation of the National Ignition Facility

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is scheduled for completion in 2009. Thereafter, experiments will commence in which capsules of DT will be imploded, generating neutrons, gammas, x-rays, and other reaction products that will interact in the facility's structure. In order to understand and minimize the exposure of workers within the facility to prompt and delayed (activation) dose, they have developed a model for the facility using the three-dimensional Monte Carlo particle transport code, TART. To obtain acceptable statistics in a reasonable amount of time, biasing techniques are employed. In an effort to improve efficiency, they are studying the optimization of particle splitting using geometrically similar, but much simpler models. They are discussing their techniques and results

Charge Carrier Density and signal induced in a CVD diamond detector from NIF DT neutrons, x-rays, and electrons

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 10{sup 15} e-h+/cm{sup 3} and 2.6* 10{sup 12} e-h+/cm{sup 3} respectively, which is lower than the 10{sup 16} e-h+/cm{sup 3} 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 10{sup 11} x-rays/cm{sup 2} (with x-ray energies varying from 6 keV to about 10 keV) or 10{sup 9} {beta}/cm{sup 2} (corresponding to 400 pC per electron pulse, E{sub {beta}} > 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 10{sup 8} x-rays/cm{sup 2} (6 to 10 keV) or 10{sup 6} {beta}/cm{sup 2} (1 pC per electron pulse, E{sub {beta}} > 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 10{sup 4} x-rays/ns/cm{sup 2} at 10 m from the source. The maximum white beam x-ray flux (thus all energies of x-rays are used) is about 10{sup 6} x-rays/ns/cm{sup 2} at 10 m from the source. These numbers are well below the necessary 10{sup 11} x-rays/cm{sup 2} 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 10{sup 11} x-rays/cm{sup 2} 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

Using X-Rays to Test CVD 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 (DT) 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 carriers 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%

A High Energy X-ray Imager for Inertial Confinement Fusion at the National Ignition Facility

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

Recovery of CVD Diamond Detectors using Laser Double Pulses

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{sub 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

Recovery of a CVD diamond detection system from strong pulses of laser produced x-rays

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

Saturation of CVD Diamond Detectors

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 surrounding electronics. In a first experiment, the laser beam energy was increased from a few tens of a pJ to about 100 µJ, 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 (Ebandgap = 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

Human TRIM Gene Expression in Response to Interferons

Tripartite motif (TRIM) proteins constitute a family of proteins that share a conserved tripartite architecture. The recent discovery of the anti-HIV activity of TRIM5α in primate cells has stimulated much interest in the potential role of TRIM proteins in antiviral activities and innate immunity.To test if TRIM genes are up-regulated during antiviral immune responses, we performed a systematic analysis of TRIM gene expression in human primary lymphocytes and monocyte-derived macrophages in response to interferons (IFNs, type I and II) or following FcγR-mediated activation of macrophages. We found that 27 of the 72 human TRIM genes are sensitive to IFN. Our analysis identifies 9 additional TRIM genes that are up-regulated by IFNs, among which only 3 have previously been found to display an antiviral activity. Also, we found 2 TRIM proteins, TRIM9 and 54, to be specifically up-regulated in FcγR-activated macrophages.Our results present the first comprehensive TRIM gene expression analysis in primary human immune cells, and suggest the involvement of additional TRIM proteins in regulating host antiviral activities