2007 Annual Report

• Complete issue
• About the cover

The fiscal year ending in September 2007 concluded the fifth year of the five-year renewal of Cooperative Agreement DE-FC52-92F19460 with the U.S. Department of Energy. This report summarizes progress in laser-fusion research at the Laboratory for Laser Energetics (LLE) during the past fiscal year. It also reports on LLE’s progress on laser, optical materials, and advanced technology development; work on the OMEGA EP (extended performance) laser project; operation of OMEGA for the National Laser Users’ Facility (NLUF) and other external users; and programs focusing on the education of high school, undergraduate, and graduate students during the year.

The laser-fusion research program at the University of Rochester’s Laboratory for Laser Energetics (LLE) is focused on the National Nuclear Security Administration’s (NNSA’s) Campaign-10 inertial confinement fusion (ICF) ignition and experimental support technology, operation of facilities (OMEGA), and the construction of OMEGA EP�a high-energy petawatt laser system. While LLE is the lead laboratory for research into the direct-drive approach to ICF ignition, it also takes a lead role in certain indirect-drive tasks within the National Ignition Campaign.

During this past year progress in the laser-fusion research program was made in three principal areas: OMEGA direct-drive and indirect-drive experiments and targets; development of diagnostics for experiments on OMEGA, OMEGA EP, and the National Ignition Facility (NIF); and theoretical analysis and design efforts aimed at improving direct-drive-ignition capsule designs and advanced ignition concepts such as fast ignition and shock ignition.

In FY07, LLE scientists in collaboration with scientists from the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC) inferred, for the first time, a neutron-averaged areal density in excess of 200 mg/cm² from direct-drive cryogenic D₂ implosions on the OMEGA laser. This set of measurements completed an NNSA Level-2 milestone and demonstrated conclusively that hydrogen can be compressed to fuel densities required for both indirect- and direct-drive-ignition capsules. The neutron-averaged areal density was inferred from the energy loss of secondary protons produced in the core along five different directions. The measured particle spectra were in close agreement with LILAC 1-D code predictions, indicating that the fuel assembly proceeded according to 1-D simulations up to the peak density of the implosions, i.e., ~140 g/cc (or approximately 700 times the density of liquid deuterium). Results of these experiments were presented at the 49th Annual Meeting of the American Physical Society Division of Plasma Physics and have been submitted for publication.

This report also includes articles on advanced-technology development projects at LLE, including the development of theoretical models for high-power fiber lasers, research on holographic volume Bragg gratings (VBG’s), experimental and theoretical studies of the time-resolved generation and detection of coherent acoustic phonons (CAP’s) in very-high-quality GaN single crystals, and the development of process technology for the fabrication of high-damage-resistance, large-aperture multilayer dielectric diffraction gratings.

The OMEGA EP project is in its fifth year. In FY07 an allocation of $2.25 million completed the $89 million funding required for the project. The project will be completed in April 2008.

The OMEGA facility conducted 1514 target shots for a variety of users in FY07. The OMEGA Availability and Experimental Effectiveness averages for the year were 92.8% and 95.9%, respectively. Highlights of the year included the following: a total of 27 D₂ and 17 DT low-adiabat cryogenic target implosions that required high-contrast pulse shapes were performed; an offline OMEGA frequency-conversion-crystal (FCC) tuning test bed was developed; more than 25 new or significantly modified target-diagnostic systems were qualified for use on the OMEGA Experimental Facility in FY07. These diagnostics supported LLE, LLNL, LANL, AWE, and CEA experiments; and significant modifications were made to the OMEGA Laser Facility in FY07 to integrate the OMEGA EP short-pulse beam into the OMEGA target chamber.

More than half (54%) of the OMEGA shots in FY07 were dedicated to external users including the NLUF programs, LLNL, LANL, SNL, CEA, and AWE.

As the only major university participant in the National ICF Program, education continues to be an important mission of LLE. Nearly 180 University of Rochester students have earned Ph.D. degrees at LLE since its founding. There are currently 77 graduate students doing research at the Laboratory and approximately 68 undergraduate students are employed by LLE during the academic year and summer. During the summer, up to 15 high-school students participate in a summer research program.