[en] From fundamental principles, an analytic model is developed for energetic electrons interacting with hydrogenic plasmas. From a unified point of view this model treats, in contrast to earlier models, the effects of stopping, straggling, and beam blooming, a consequence of multiple scattering and energy loss. The model can treat either the case of partial or entire energy loss. Enhanced energy deposition, which occurs in the latter portion of the penetration, is found to be inextricably linked to straggling and beam blooming. For energy deposition, the following picture emerges: initially, a region of nearly uniform energy deposition occurs, but as the electron loses more energy, an extended region of enhanced, non-uniform energy deposition comes into play. This present work has important impacts on quantitatively evaluating energy deposition of the energetic electrons in various plasmas, including inertial confinement fusion plasmas and relativistic astrophysical jets. In the case of FI, for example, hitherto there have been no evaluations which have treated either straggling or blooming upon the energy deposition, without which there can be no confident assessment of ignition requirements. The calculations herein therefore forms a foundation for a baseline, at the very least, or an accurate assessment, at the very most, by which to evaluate these effects upon fast ignition. (Author)

[en] The coefficients of the KL mix model were set by Dimonte to match RT and RM instabilities as measured on the Linear Electric Motor (LEM). The KL mix model has been applied to directly-driven capsule implosions with a variety of laser energies, ablator materials, ablator thicknesses and convergence ratios. The KL calculations nearly match the observed Y_DD, Y_DT, Y_P, T_ion and implosion times for many (but not all) capsules

[en] The basis for a time-of-flight neutron spectrometer for inertial confinement fusion (ICF) experiments using recoils from a shaped scattering foil is presented. It is shown that the number of elastic recoils can be substantially increased by utilizing a large scattering foil in the shape of an ellipsoid, with the curvature of the ellipsoid being determined by the mass of the recoil particle. This shape allows the time-of-flight dispersion -- present originally in the neutrons -- to be maintained in the recoils despite the large foil area. The feasibility of using this design on current ICF experiments is discussed

[en] An analytic model is developed for energetic electrons interacting with plasmas. This model rigorously treats the effects of energy loss upon Coulomb interactions and reveals several important features, including the coupling of scattering and energy loss--which previous calculations had erroneously treated as independent in cases where an electron lost a significant amount (or all) of its energy. The unique transparency and generality of these calculations allows for straightforward applications when quantitatively evaluating the energy deposition of energetic electrons in various plasmas, including those in inertial confinement fusion.

[en] From fundamental principles, the interaction of directed energetic electrons with hydrogenic and arbitrary-Z plasmas is analytically modeled. The effects of stopping, straggling, and beam blooming, a consequence of scattering and energy loss, are rigorously treated from a unified approach. Enhanced energy deposition occurs in the latter portion of the penetration and is inextricably linked to straggling and blooming. These effects, which have a strong Z dependence, will be important in evaluating the requirements of fast ignition and tolerable levels of electron preheat

[en] With charged-particle spectroscopy implemented on OMEGA, we have been able to routinely measure the particle spectra (both nuclear lines and continua) from a variety of capsule implosions. Important parameters such as fusion yields, fuel and shell areal densities, and ion temperatures can be readily deduced. We will report on details of this work with emphasis on the implosion physics

[en] The use of measured spectra of secondary fusion protons for studying physical characteristics of D₂-filled inertial confinement fusion capsules is described theoretically and demonstrated with data from implosions in the OMEGA 60-beam laser facility. Spectra were acquired with a magnet-based charged-particle spectrometer and with a range-filter-based spectrometer utilizing filters and CR39 nuclear track detectors. Measurement of mean proton energy makes possible the study of a capsule's total areal density (ρR), since that is what affects the energy loss suffered by protons as they pass through fuel and shell while leaving the capsule. Details of specific shots will be presented. It is also shown that similar techniques should prove useful for diagnosis of future experiments with cryogenic D₂-filled capsules

[en] Fast protons ∼>1 MeV have been observed on the 60-beam, 30 kJ OMEGA laser [T. R. Boehly , Opt. Commun. 133, 495 (1997)] at an intensity I≅10¹⁵ W/cm² and a wavelength λ=0.35 μm. These energies are more than 5 times greater than those observed on previous, single-beam experiments at the same Iλ². The total energy in the proton spectrum above 0.2 MeV is ∼0.1% of the laser energy. Some of the proton spectra display intense, regular lines which may be related to ion acoustic perturbations in the expanding plasma

[en] Spectral measurements have been made of charged fusion products produced in deuterium + helium-3 filled targets irradiated by the OMEGA laser system [T. R. Boehly , Opt. Commun. 133, 495 (1997)]. Comparing the energy shifts of four particle types has allowed two distinct physical processes to be probed: Electrostatic acceleration in the low-density corona and energy loss in the high-density target. When the fusion burn occurred during the laser pulse, particle energy shifts were dominated by acceleration effects. Using a simple model for the accelerating field region, the time history of the target electrostatic potential was found and shown to decay to zero soon after laser irradiation was complete. When the fusion burn occurred after the pulse, particle energy shifts were dominated by energy losses in the target, allowing fundamental charged-particle stopping-power predictions to be tested. The results provide the first experimental verification of the general form of stopping power theories over a wide velocity range

[en] The generation of strong, self-generated electric fields (GV/m) in direct-drive, inertial-confinement-fusion (ICF) capsules has been reported [Rygg et al., Science 319, 1223 (2008); Li et al., Phys. Rev. Lett. 100, 225001 (2008)]. A candidate explanation for the origin of these fields based on charge separation across a plasma shock front was recently proposed [Amendt et al., Plasma Phys. Controlled Fusion 51 124048 (2009)]. The question arises whether such electric fields in imploding capsules can have observable consequences on target performance. Two well-known anomalies come to mind: (1) an observed ≅2x greater-than-expected deficit of neutrons in an equimolar D³He fuel mixture compared with hydrodynamically equivalent D [Rygg et al., Phys. Plasmas 13, 052702 (2006)] and DT [Herrmann et al., Phys. Plasmas 16, 056312 (2009)] fuels, and (2) a similar shortfall of neutrons when trace amounts of argon are mixed with D in indirect-drive implosions [Lindl et al., Phys. Plasmas 11, 339 (2004)]. A new mechanism based on barodiffusion (or pressure gradient-driven diffusion) in a plasma is proposed that incorporates the presence of shock-generated electric fields to explain the reported anomalies. For implosions performed at the Omega laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)], the (low Mach number) return shock has an appreciable scale length over which the lighter D ions can diffuse away from fuel center. The depletion of D fuel is estimated and found to lead to a corresponding reduction in neutrons, consistent with the anomalies observed in experiments for both argon-doped D fuels and D³He equimolar mixtures. The reverse diffusional flux of the heavier ions toward fuel center also increases the pressure from a concomitant increase in electron number density, resulting in lower stagnation pressures and larger imploded cores in agreement with gated, self-emission, x-ray imaging data.