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INERTIAL CONFINEMENT LawrenceLawrence LivermoreLivermore NationalNational LaboratoryLaboratory UCRL-LR-105821-96 ICF Annual Report 1996 This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California and shall not be used for advertising or product endorsement purposes. This report has been reproduced directly from the best available copy. Available to DOE and DOE contractors from the Office of Scientific and Technical Information P.O. Box 62, Oak Ridge, TN, 37831 Prices available from (615) 576-8401, FTS 626-8401 Available from the National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, Virginia 22161 Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract WÐ7405ÐEngÐ48. INERTIAL CONFINEMENT FUSION 1996 ICF Annual Report UCRL-LR-105821-96 Distribution Category UC-712 October 1995ÐSeptember 1996 Printed in the United States of America MS Date Available from June 1997 National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, Virginia 22161 Price codes: printed copy A03, microfiche A01. Lawrence Livermore National Laboratory FOREWORD The ICF Annual Report provides documentation of the achievements of the LLNL ICF Program during the fiscal year by the use of two formats: (1) an Overview that is a narra- tive summary of important results for the fiscal year and (2) a compilation of the articles that previously appeared in the ICF Quarterly Report that year. Both the Annual Overview and Quarterly Report are also on the Web at http://lasers.llnl.gov/lasers/pubs/icfq.html. The underlying theme for LLNLÕs ICF Program research is defined within DOEÕs Defense Programs missions and goals. While in pursuit of its goal of demonstrating ther- monuclear fusion ignition and energy gain in the laboratory, the ICF Program provides research and development opportunities in fundamental high-energy-density physics and supports the necessary research base for the possible long-term application of inertial fusion energy for civilian power production. ICF technologies continue to have spin-off applications for additional government and industrial use. LLNLÕs ICF Program falls within DOEÕs national ICF program that includes the Nova and Beamlet (LLNL), OMEGA (University of Rochester Laboratory for Laser Energetics), Nike (Naval Research Laboratory), and Trident (Los Alamos National Laboratory) laser facilities. The Particle Beam Fusion Accelerator and Saturn pulsed power facilities are at Sandia National Laboratories. General Atomics, Inc., develops and provides many of the targets for the above experimental facilities. Many of the Quarterly Report articles are co-authored with colleagues from these other ICF institutions. Questions and comments relating to the content of the journal should be addressed to the ICF Program Office, Lawrence Livermore National Laboratory, P.O. Box 808, L-488, Livermore, CA 94551. Jason Carpenter Publication Editor Don Correll Managing Editor iii ACKNOWLEDGMENTS We thank the 28 authors and their co-authors who contributed to this Annual Report. Their work, published in our four Quarterly Reports, is compiled here to highlight LLNLÕs ICF Program accomplishments for the year. We are grateful for their willingness to take time from busy schedules to write the articles that describe their work. We thank the four Quarterly Report Scientific Editors Randall McEachern, Deanna Pennington, Alan Burnham, and Michael Marinak for their efforts and diligent review to ensure the quality of each Quarterly Report. We thank Roy Johnson for his careful classification reviews. We also thank the secretaries for typing manuscripts, arranging meetings, and offering other invaluable assistance. We thank Technical Information Department (TID) editors Jason Carpenter, Robert Kirvel, Al Miguel, Peter W. Murphy, Ann Parker, Joy PŽrez, Margaret A. Sands, and Dabbie P. Schleich for editing and managing the production cycle; and artists/designers Pamela Davis, Daniel S. Moore, Linda L. Wiseman, and Sandy Lynn for providing expertise in graphic design and layout. We appreciate the support of Michael Gallardo, the Government Printing Office Coordinator, who worked with the Government Printing Office to obtain high-quality printing; and Mary Nijhuis of TIDÕs Publications Services and TIDÕs Print Plant for making sure that each publication was distributed with dispatch. The talents and dedication of the ICF Program staff make the ICF Annual what it is for so many of its readers. John Lindl ICF Science Director Don Correll ICF Operations Manager iv TABLE OF CONTENTS TABLE OF CONTENTS Foreword iii Acknowledgments iv ICF Program Overview ix Theory and Simulations of Nonlinear SBS in 1 Multispecies Plasmas Gas-filled hohlraums are the preferred targets for indirect-drive fusion experiments planned for the National Ignition Facility. However, instabilities like stimulated Brillouin scattering in the gas may reflect large amounts of laser light out of the hohlraum. We report on a method developed to control this instabilityÑa small amount of hydrogen added to the gas strongly decreases the reflected light. Modeling of Self-Focusing Experiments by Beam 7 Propagation Codes To validate the codes PROP1 and PROP2, we used data from two 1053-nm self-focusing experiments in fused silica. Self-focusing damage in the sample was induced by placing a large wire in the beam in front of the silica sample. Using a small wire, damage to the sample was avoided, and induced lensing in the sample produced an intense image of the wire. Using the measured beam profiles and waveforms as input, and the value 2.7 × 10Ð16 cm2/W for the self-focusing coefficient in silica, the codes successfully predicted the length of the self-focusing tracks and the intensity in the induced image. Gas-Filled Target Designs Produce Ignition-Scale Plasma 15 Conditions with Nova Gas-filled targets provide large, uniform underdense plasmas for laserÐplasma interaction experiments on Nova. This article discusses design considerations for these targets and presents calculated plasma profiles, target characterization results, and comparisons with underdense plasma parameters in ignition hohlraum designs for the National Ignition Facility. Stimulated Brillouin Scattering in Multispecies Plasmas 22 Laser light propagating through the underdense plasma in a hohlraum, or the corona of a direct-drive target, is subject to stimulated Brillouin scattering (SBS). Such scattering can cause significant loss of incident laser energy and/or affect the symmetry of the implosion. This article discusses the use of mixtures (e.g., H/He) to tailor the Landau damping of the SBS driven ion acoustic waves, thereby providing a powerful method to control the instability. Optical ScatterÑA Diagnostic Tool to Investigate Laser 27 Damage in KDP and DKDP Determining and controlling the sources of laser-induced damage in crystals of KH2PO4 and deuterated KDP is important for successful production of crystals for the National Ignition Facility. This article describes the implementation of a scatter diagnostic for in situ studies of laser- induced damage and initial results from these studies. Soft X-Ray Interferometry 32 The short wavelength of existing soft x-ray lasers makes them well suited to probing large high- density plasmas. We have combined a multilayer optic-based interferometer and a 155 • x-ray laser source to measure the electron density profile in millimeter-size laser-produced plasmas. Metastable Crystal Structures of Solid Hydrogen 38 We have determined the crystal structure of vapor deposited H2 or D2 crystals using Raman spectroscopy. While hcp is the equilibrium crystal structure, other metastable crystal structures can be formed at low deposition temperatures. Non-hcp crystals transform to hcp continuously and irreversibly by increasing the temperature to about half the triple point temperature. We also measured the crystal grain size as a function of deposition temperature and deposition rate. v TABLE OF CONTENTS X-Ray Production in Laser-Heated Xe Gas Targets 43 We measured x-ray production in Xe-filled gas-bag targets heated using the Nova laser at 21 kJ of 0.35-µm light in a 1-ns pulse. X-ray production in the 0.1 to 2-keV region is ~60% of the incident laser light and is comparable to x-ray production efficiency from Au disks. X-ray production efficiency of Xe L-shell x rays in the 4 to 5-keV range is ~8% and is higher than disk- target efficiencies in this x-ray energy range. Measurement of 0.35-µm Laser Imprint in a Thin Si Foil Using an X-Ray Laser Backlighter 49 We describe measurements of the modulation in optical depth imprinted in thin Si foils by direct 0.35-µm laser irradiation at low intensities and with static random phase plate and one- dimensional (1-D) smoothing by spectral dispersion (SSD). These measurements were made at the time of shock breakout using an x-ray laser backlighter at 15.5 nm with a multilayer optics imaging system. Measurements of the imprinted modulation are compared with the optical speckle pattern and smoothing due to 1-D SSD. Absorption of Laser Light in Overdense Plasmas by Sheath Inverse Bremsstrahlung 55 This article describes our modification of the original sheath inverse bremsstrahlung model and how we achieved significantly different results from those derived without the v × B term.