Progress in direct-drive inertial confinement fusion research at the laboratory for laser energetics

Direct-drive inertial confinement fusion (ICF) is expected to demonstrate high gain on the National Ignition Facility (NIF) in the next decade and is a leading candidate for inertial fusion energy production. The demonstration of high areal densities in hydrodynamically scaled cryogenic DT or D₂ implosions with neutron yields that are a significant fraction of the “clean” 1-D predictions will validate the ignition-equivalent direct-drive target performance on the OMEGA laser at the Laboratory for Laser Energetics (LLE). This paper highlights the recent experimental and theoretical progress leading toward achieving this validation in the next few years. The NIF will initially be configured for X-ray drive and with no beams placed at the target equator to provide a symmetric irradiation of a direct-drive capsule. LLE is developing the “polar-direct-drive” (PDD) approach that repoints beams toward the target equator. Initial 2-D simulations have shown ignition. A unique “Saturn-like” plastic ring around the equator refracts the laser light incident near the equator toward the target, improving the drive uniformity. LLE is currently constructing the multibeam, 2.6-kJ/beam, petawatt laser system OMEGA EP. Integrated fast-ignition experiments, combining the OMEGA EP and OMEGA Laser Systems, will begin in FY08.     

Combinatorial synthesis and characterization of a ternary epitaxial film of Co and Mn doped Ge (0 0 1)

We report combinatorial molecular beam epitaxy synthesis and properties of a ternary epitaxial film of Co and Mn co-doped Ge grown on Ge (0 0 1) substrate. Structural effects were examined in situ by reflection high-energy electron diffraction and ex situ by microbeam X-ray diffraction techniques, and magnetic properties were probed by using magnetooptic Kerr effect. Ternary epitaxial phase diagrams have been studied for total doping concentrations up to 30 at.%, where regions of coherent epitaxy and rough disordered growth and those of near room temperature ferromagnetic ordering have been identified.     

Diffusion of 111Cd probes in Ga7Pt3 studied via nuclear quadrupole relaxation

Diffusion of ¹¹¹In/Cd impurity atoms was studied in Ga₇Pt₃ at the atomic level using the method of perturbed angular correlation of gamma rays (PAC). As in previous measurements on Ga₇Pd₃, probes were observed to occupy two inequivalent Ga-sublattices. Quadrupole interaction perturbation functions for each site exhibited damping at elevated temperatures that is attributed to nuclear relaxation caused by stochastic jumps of the probe atoms accompanied by reorientation of axes of the electric field gradient tensor. Fitted relaxation frequencies, proportional to mean jump frequencies of the probe, were thermally activated. Arrhenius plots revealed jump-frequency activation enthalpies of 0.94 (8) and 0.67 (4) eV for the two sites and frequency prefactors close to 1 THz. Results were similar to those found previously for Ga₇Pd₃, although jump frequencies are about 100 times lower in Ga₇Pt₃.     

NEUROTOXICITY OF TETRAPHENYLPORPHINESULFONATE TPPS4 and ITS RELATION TO PHOTODYNAMIC THERAPY*

Abstract Tetraphenylporphinesulfonate (TPPS₄) is a synthetic porphyrin that localizes in certain tumors to a higher absolute concentration and with more favorable tumor to other tissue ratios than any other porphyrin yet studied. Its utilization for photodynamic therapy and other applications has been inhibited by reported neurotoxicity. We injected TPPS₄ over a broad dose range of 5-150 mg kg^?1 and observed the effects on peripheral nerve in groups of animals sacrificed 35, 70 and 140 days later. No immediate deaths or phototoxic manifestations were seen. Light and electron microscopy, however, revealed cytoskeletal abnormalities and nerve fiber degeneration affecting both myelinated and unmyelinated fibers in all the time and dose groups. These findings have similarities to those of other experimental toxic neuropathies, and may also be related to the preponderance of autonomic manifestations in patients with porphyric neuropathy. The morphological changes consisted of tangles of fibrillar material in the myelinated fibers and loss of neurotubules in the unmyelinated fibers. Our studies indicate a direct interaction of TPPS₄ with tubulin. This biological mechanism may be involved in the selective distribution of certain parenterally administered porphyrins.     

Individual interface states and their implications for low-frequency noise in MOSFETs

We show that the wide distribution of time constants required to explain 1/ƒ noise in MOSFETs arises as a natural consequence of the multi-phonon model of carrier trapping into individual Si-SiO₂ interface states. A new class of random telegraph signal found in the drain current of small-area silicon MOSFETs is described. These signals are a result of defect metastability and are shown to be a source of non-Gaussian noise.     

Site Preferences of Hyperfine Impurities in Ni2Al3 Phases

The site occupation of indium solutes in Ni₂Al₃-type compounds was determined using perturbed angular correlation of gamma rays. Measurements were made for compositions on both sides of the stoichiometric composition. Sites were identified through their quadrupole interactions. For transition-metal (TM) rich aluminides and galliumides, indium solutes occupy only one of two inequivalent trivalent-metal sites (Al or Ga). For TM-poor aluminides, indium solutes tend to locate at noncrystallographic sites such as in grain boundaries. For TM-poor galliumides, the solutes occupy nickel sites while close to the stoichiometric composition they also occupy sites on an empty Ni-sublattice. Composition dependences of site preference for indium solutes in Pt₂Al₃ and Ni₂Ga₃ are examined in terms of a recently developed thermodynamic model. This revised version was published online in September 2006 with corrections to the Cover Date.     

Thermally degradable maleimides for reworkable adhesives

New thermosetting materials were developed for reworkable adhesive applications by introducing acetal ester groups as thermally degradable linkages into maleimide compounds. The synthesis of compounds containing maleimide functionality and acetal ester linkages was conducted by a one‐step neat reaction from commercially available materials. The polymerization process and thermal degradation of the synthesized materials were studied. It was found that the acetal ester linkage degraded rapidly above 225 °C, and introduction of this linkage into the adhesive formulation led to improved reworkability of adhesively bonded substrates. A mechanism for reworkability was proposed based on the insight provided by experimental and modeling work. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1073–1084, 2009