Planar laser-plasma interaction (LPI) experiments at the National Ignition Facility (NIF) have allowed access for the first time to regimes of electron density scale length (∼500 to 700 μm), ...electron temperature (∼3 to 5 keV), and laser intensity (6 to 16×10^{14} W/cm^{2}) that are relevant to direct-drive inertial confinement fusion ignition. Unlike in shorter-scale-length plasmas on OMEGA, scattered-light data on the NIF show that the near-quarter-critical LPI physics is dominated by stimulated Raman scattering (SRS) rather than by two-plasmon decay (TPD). This difference in regime is explained based on absolute SRS and TPD threshold considerations. SRS sidescatter tangential to density contours and other SRS mechanisms are observed. The fraction of laser energy converted to hot electrons is ∼0.7% to 2.9%, consistent with observed levels of SRS. The intensity threshold for hot-electron production is assessed, and the use of a Si ablator slightly increases this threshold from ∼4×10^{14} to ∼6×10^{14} W/cm^{2}. These results have significant implications for mitigation of LPI hot-electron preheat in direct-drive ignition designs.
An international panel reviewed the methodology for clinical trials of spinal cord injury (SCI), and provided recommendations for the valid conduct of future trials. This is the second of four ...papers. It examines clinical trial end points that have been used previously, reviews alternative outcome tools and identifies unmet needs for demonstrating the efficacy of an experimental intervention after SCI. The panel focused on outcome measures that are relevant to clinical trials of experimental cell-based and pharmaceutical drug treatments. Outcome measures are of three main classes: (1) those that provide an anatomical or neurological assessment for the connectivity of the spinal cord, (2) those that categorize a subject's functional ability to engage in activities of daily living, and (3) those that measure an individual's quality of life (QoL). The American Spinal Injury Association impairment scale forms the standard basis for measuring neurologic outcomes. Various electrophysiological measures and imaging tools are in development, which may provide more precise information on functional changes following treatment and/or the therapeutic action of experimental agents. When compared to appropriate controls, an improved functional outcome, in response to an experimental treatment, is the necessary goal of a clinical trial program. Several new functional outcome tools are being developed for measuring an individual's ability to engage in activities of daily living. Such clinical end points will need to be incorporated into Phase 2 and Phase 3 trials. QoL measures often do not correlate tightly with the above outcome tools, but may need to form part of Phase 3 trial measures.
Three-dimensional laser-plasma interaction simulations show that laser frequency detuning by an amount achievable with current laser technology can be used to suppress the two-plasmon decay (TPD) ...instability and the corresponding hot-electron generation. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion implosion on the OMEGA laser, the simulations show that ∼0.7% laser frequency detuning is sufficient to eliminate TPD-driven hot-electron generation in current experiments. This allows for higher ablation pressures in future implosion designs by using higher laser intensities.
The linear stability of multiple coherent laser beams with respect to two-plasmon-decay instability in an inhomogeneous plasma in three dimensions has been determined. Cooperation between beams leads ...to absolute instability of long-wavelength decays, while shorter-wavelength shared waves are shown to saturate convectively. The multibeam, in its absolutely unstable form, has the lowest threshold for most cases considered. Nonlinear calculations using a three-dimensional extended Zakharov model show that Langmuir turbulence created by the absolute instability modifies the convective saturation of the shorter-wavelength modes, which are seen to dominate at late times.
Half-harmonic emission spectra and images taken during directly driven implosions show that the two-plasmon decay (TPD) instability is driven nonuniformly over the target surface and that multibeam ...effects dominate this instability. The images show a spatially limited extent of the TPD instability. A prominent spectral feature is used to determine the electron temperature in the corona. Near threshold the temperatures agree with one-dimensional hydrodynamic predictions but exceed them by ∼10% above the TPD threshold. Two-dimensional hydrodynamic simulations indicate that a significant part (∼20%) of the laser intensity must be locally absorbed by the TPD instability (i.e., by collisional damping of the electron plasma waves) to maintain these temperature islands.
A ground-based Fourier transform spectrometer has been developed to measure the atmospheric downwelling infrared radiance spectrum at the earth's surface with high absolute accuracy. The Atmospheric ...Emitted Radiance Interferometer (AERI) instrument was designed and fabricated by the University of Wisconsin Space Science and Engineering Center (UW-SSEC) for the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program. This paper emphasizes the key features of the UW-SSEC instrument design that contribute to meeting the AERI instrument requirements for the ARM Program. These features include a highly accurate radiometric calibration system, an instrument controller that provides continuous and autonomous operation, an extensive data acquisition system for monitoring calibration temperatures and instrument health, and a real-time data processing system. In particular, focus is placed on design issues crucial to meeting the ARM requirements for radiometric calibration, spectral calibration, noise performance, and operational reliability. The detailed performance characteristics of the AERI instruments built for the ARM Program are described in a companion paper. PUBLICATION ABSTRACT
• We present a 10-year sequence of soil water measurements under eucalypt plantations. • Soil water declines throughout the 1st rotation at many sites. • Soil water is fully replenished at only 1 of ...3 experimental sites in the 2nd rotation. • Modeling shows that many sites will not be fully replenished in the 2nd rotation. • Managers will need to consider fallowing to maintain productivity in the 2nd rotation.
Eucalyptus globulus plantations are thought to use stored soil water when planted on ex-agricultural sites, and we hypothesized that this is likely to affect productivity of 2nd and later rotation plantations because the next rotations have access to less stored soil water. We used a combination of experiments and modeling to understand the impact of E. globulus plantations on soil water stores over the first rotation and early second rotation. The experiments were conducted at 3 contrasting sites in south-western Australia, and modeling was used to extrapolate the results to other climatic zones. Soil water dynamics were assessed to 8m depth under a range of management options, including spacing and nitrogen addition in the first rotation, and coppice or seedling re-establishment in the 2nd rotation. We found that soil water stores declined over the course of the first rotation at all sites, with some (incomplete) annual replenishment evident at the higher rainfall sites, but less replenishment at depth, especially in the lower rainfall sites. Only the wettest of the 3 sites fully replenished with soil water after harvest of the 1st rotation. Plots with higher stocking rates had higher soil water depletion early in the rotation, although by the end of the first rotation, most treatments had similar soil water deficits of around 800mm at all of the sites. Of the sites that were responsive to N fertilizer, there was a strong differential in the degree of soil water deficit between N treatments, with N fertilized trees using more of the soil water store each year, but also producing more wood. A process-based plantation growth model, CABALA, was found to be adequate for predicting soil water dynamics under the range of management options that we explored, and we applied it to understanding the potential replenishment of soil under 2nd rotation plantations in a range of climatic zones within the E. globulus estate in south-western Australia. This modeling showed that most sites with soil depths of more than 4m (i.e., most of the estate) are unlikely to be fully replenished in the 2nd rotation, and that this is likely to have a significant impact on the capacity of sites to achieve similar productivity levels in the second rotation as the first unless the sites are given an opportunity for soil water replenishment between rotations. The results from this study suggest that plantation managers will need to understand soil water dynamics at any given site to be able to predict productivity in 2nd and later rotations, and may need to explore novel management options like fallowing between rotations to allow for soil water replenishment.
Abstract
The Atmospheric Emitted Radiance Interferometer (AERI) instrument was developed for the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program by the University of ...Wisconsin Space Science and Engineering Center (UW-SSEC). The infrared emission spectra measured by the instrument have the sensitivity and absolute accuracy needed for atmospheric remote sensing and climate studies. The instrument design is described in a companion paper. This paper describes in detail the measured performance characteristics of the AERI instruments built for the ARM Program. In particular, the AERI systems achieve an absolute radiometric calibration of better than 1% (3σ) of ambient radiance, with a reproducibility of better than 0.2%. The knowledge of the AERI spectral calibration is better than 1.5 ppm (1σ) in the wavenumber range 400– 3000 cm−1.
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