[en] We developed a reduced description of kinetic effects that is included in a fluid model of stimulated Brillouin backscattering (SBS) in low Z plasmas (e.g. He, Be). Following hybrid-PIC simulations, the modified ion distribution function is parametrized by the width (delta) of the plateau created by trapping around the phase velocity of the SBS-driven acoustic wave. An evolution equation is derived for (delta) , which affects SBS through a frequency shift and a reduced Landau damping. This model recovers the linear Landau damping value for small waves and the time-asymptotic nonlinear frequency shift calculated by Morales and O'Neil. Finally we compare our reduced model with Bzohar simulations of a Be plasma representative of experiments that have shown evidence of ion trapping

[en] In modern 2D and 3D PIC simulations relevant to National Ignition Facility (NIF) parameters, the low frequency magnetic fields associated with the localized fast electron currents generated by Stimulated Raman Scatter have been identified. We consider electron plasma densities from 0.1 to 0.2 of critical density (n_c) and electron plasma temperatures (T_e) from a few keV to over 10 keV in simulations with space scales corresponding to a laser speckle in modeling with our massively parallel PIC code 23. These magnetic fields are ∼ 1 MG, Then the electrons accelerated by the Raman process are magnetized with their Lamor radii on the order of a speckle width. The transport of these hot electrons out of the speckle then becomes a more complex process than generally assumed

[en] The widely differing spatial, temporal, and density scales needed to accurately model the fast ignition process and other short-pulse laser-plasma interactions leads to a computationally challenging project that is difficult to solve using a single code. This report summarizes the work performed on a three year LDRD to couple together three independent codes using PYTHON to build a new integrated computational tool. An example calculation using this new model is described

[en] Light propagating down a cone and/or impinging on a structured surface in the short-pulse, high intensity laser-matter interaction which generates the hot energetic electrons essential to the fast ignition scheme is studied with particle-in-cell simulations. These more complex geometries lead to both increased laser light absorption and higher temperatures of the resulting energetic electrons as compared to simple slab interactions. But the relatively wide angular distributions of the energetic electrons observed in the simulations needs to be taken into account in fast ignition designs.

[en] We have made the first detailed measurements of a diffusive supersonic radiation wave in the laboratory. A 10 mg/cm³ SiO₂ foam is radiatively heated by the x-ray flux from a laser-irradiated hohlraum. The resulting radiation wave propagates axially through the optically thick foam and is measured via time-resolved x-ray imaging as it breaks out the far end. The data show that the radiation wave breaks out at the center prior to breaking out at the edges, indicating a significant curvature in the radiation front. This curvature is primarily due to energy loss into the walls surrounding the foam. (c) 2000 The American Physical Society

[en] We have designed an experimental technique to use on the National Ignition Facility (NIF) laser to achieve very high pressure (P_max > 10 Mbar = 1000 GPa), dense states of matter at moderate temperatures (kT < 0.5 eV = 6000 K), relevant to the core conditions of the giant planets. A discussion of the conditions in the interiors of the giant planets is given, and an experimental design that can approach those conditions is described

[en] A crucial issue for the viability of the fast ignition approach to inertial fusion energy is the transport of the ignition pulse energy from the critical surface to the high-density compressed fuel. Experiments have characterized this transport through the interaction of short pulse, high intensity lasers with solid-density targets containing thin K_alpha fluorescence layers. These experiments show a reasonably well-collimated beam, although with a significantly larger radius than the incident laser beam. We report on LSP calculations of these experiments, which show reasonable agreement with the experimental observations

[en] Probably the most famous equation in physics is Einstein's E=mc², which was contained within his fifth and final paper that was published in 1905. It is this relationship between energy ( E) and mass ( m) that the fusion process exploits to generate energy. When two isotopes of hydrogen (normally Deuterium and Tritium (DT)) fuse they form helium and a neutron. In this process some of the mass of the hydrogen is converted into energy. In the fast ignition approach to fusion a large driver (such as the NIF laser) is used to compress the DT fuel to extremely high densities and then is ''sparked'' by a high intensity, short-pulse laser. The short-pulse laser energy is converted to an electron beam, which then deposits its energy in the DT fuel. The energy of the electrons in this beam is so large that the electron's mass is increased according to Einstein theory of relativity. Understanding the transport of this relativistic electron beam is critical to the success of fast ignition and is the subject of this poster

[en] Recent experiments at the Institute of Laser Engineering (ILE) in Japan [1] and at Rutherford Appleton Laboratory (RAL) in the United Kingdom [2] have shown good coupling of short pulse high-intensity laser light into high-energy electrons channeled down a narrow fiber. Such target configurations are being considered as backlighter targets on the National Ignition Facility (NIF). We will report on LSP calculations of these cone-wire experiments and other candidate target configurations. These calculations also give insight into the transport of MeV-electrons, which remains the critical issue for the achievement of fast ignition [3]. The LSP code uses a direct implicit particle-in-cell (PIC) algorithm in 2 or 3 dimensions to solve for beam particle transport, while treating the background particles as a fluid [4]. We have modified LSP to produce K.. photons in a non-interfering manner and will show calculated absolute K.. yields for the experiments reported by Key [2]. (Author)

[en] The Drive campaign [D A Callahan et al., this conference] on the National Ignition Facility (NIF) laser [E. I. Moses, R. N. Boyd, B. A. Remington, C. J. Keane, R. Al-Ayat, Phys. Plasmas 16, 041006 (2009)] has the focused goal of understanding and optimizing the hohlraum for ignition. Both the temperature and symmetry of the radiation drive depend on laser and hohlraum characteristics. The drive temperature depends on the coupling of laser energy to the hohlraum, and the symmetry of the drive depends on beam-to-beam interactions that result in energy transfer [P. A. Michel, S. H. Glenzer, L. Divol, et al, Phys. Plasmas 17, 056305 (2010).] within the hohlraum. To this end, hohlraums are being fielded where shape (rugby vs. cylindrical hohlraums), gas fill composition (neopentane at room temperature vs. cryogenic helium), and gas fill density (increase of ∼ 150%) are independently changed. Cylindrical hohlraums with higher gas fill density show improved inner beam propagation, as should rugby hohlraums, because of the larger radius over the capsule (7 mm vs. 5.75 mm in a cylindrical hohlraum). Energy coupling improves in room temperature neopentane targets, as well as in hohlraums at higher gas fill density. In addition cross-beam energy transfer is being addressed directly by using targets that mock up one end of a hohlraum, but allow observation of the laser beam uniformity after energy transfer. Ideas such as splitting quads into “doublets” by re-pointing the right and left half of quads are also being pursued. LPI results of the Drive campaign will be summarized, and analyses of future directions presented. (paper)