Collapsing Radiative Shock Experiments on the Omega Laser
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Collapsing Radiative Shock Experiments on the Omega Laser by Amy B. Reighard A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Physics) in The University of Michigan 2007 Doctoral Committee: Professor R. Paul Drake, Co-Chair Professor Fred C. Adams, Co-Chair Professor Carl W. Akerlof Professor James Paul Holloway Professor Gregory Tarl´e c Amy B. Reighard 2007 All Rights Reserved To Robert L. Cooper, who helped at every step along the way with love, support, and a firm grasp of reality; I hope I am just as helpful when it is your turn. To Mom and Dad, who never doubted that I should or could do this. ii ACKNOWLEDGEMENTS I would first like to thank my graduate research advisor, Paul Drake, for guid- ing me on this exciting project. Thank you for allowing me to present at a dozen conferences, for encouraging me to pursue somewhat-related tangents, for flying me across the country to “see who will wander by”, for letting me do the fun stuff while you handled the unpleasant things, and for always knowing when not to tell me the answer. Thank you also to the graduate students, past and present, in the Drake research group; Carolyn Kuranz, Eric Harding, Tony Visco, Korbie Killebrew Dannenberg, and Kelly Korreck for many useful discussions, brainstorming sessions, homework arguments, and your enduring friendship, fellowship, and support. I feel lucky to have such wonderful peers. I would like to acknowledge the extensive contributions of the Target Fabrication Team in the Drake group at the University of Michigan, especially Michael Grosskopf, Douglas Kremer, Christine Krauland, and Trisha Donajkowski, who built, trans- ported, organized, and filled my targets. Eduardo Mucino also helped extensively with 1D simulation work on beryllium, and Dave Leibrandt simulated the experiment using Zeus 2D. Thank you also to the technical staff at the Omega Laser facility, without whom none of these experiments could have been executed. Thank you especially to Keith Thorp, Steve Stagnitto, Jack Armstrong, and Chuck Source. iii I have also had many helpful discussions with an international group of collabora- tors, which includes Tom Boehly, Laurent Boireau, Serge Bouquet, Michel Busquet, Dustin Froula, Gail Glendinning, Siegfried Glenzer, Freddy Hansen, Jim Knauer, Michel Koenig, Ted Perry, Bruce Remington, Steven Ross, and Russell Wallace. Lastly, thank you to my committee, whose extensive input helped shape this thesis in a very positive way. iv TABLE OF CONTENTS DEDICATION .......................................... ii ACKNOWLEDGEMENTS .................................. iii LIST OF FIGURES ...................................... vii LIST OF TABLES ....................................... xv LIST OF APPENDICES ................................... xvii CHAPTER I. Introduction ....................................... 1 1.1 High-Energy-Density Physics . 2 1.2 A Brief History of HED physics . 2 1.3 Laboratory Astrophysics . 3 1.4 Tools of the Trade: High-Energy-Density Facilities . 6 1.4.1 High-powered laser facilities . 7 1.4.2 Z-pinches . 10 1.4.3 Petawatt Lasers . 11 II. Radiation Hydrodynamics .............................. 12 2.1 Single-Fluid Euler Equations . 13 2.2 The Equation of Radiative Transfer and Radiative Hydrodynamics . 13 2.2.1 Threshold for Radiative Shocks . 15 2.2.2 Classification for Meaningful Comparison . 16 2.2.3 Formation of a Cooling Layer and a Collapsed Shock . 17 2.2.4 Energy Balance in a Thick/Thin Shock . 21 2.3 A Brief History of Radiation Hydrodynamics Experiments . 22 III. Experiment Description ................................ 28 3.1 Targets . 29 3.2 Lasers . 33 3.3 Backlighters . 37 3.4 Diagnostics . 40 3.4.1 Microchannel Plates and Framing Cameras . 40 3.4.2 Velocity Interferometry . 43 3.4.3 Thomson scattering . 48 IV. Experimental Results ................................. 49 v 4.1 Radiographic Image Processing . 52 4.2 X-ray Radiographic Data . 56 4.2.1 Single-strip framing camera data from 40 µm beryllium drive disks 57 4.2.2 Single-strip framing camera data from 20 µm, beryllium drive disks 57 4.2.3 Single-strip framing camera data from 10 µm beryllium drive disk . 61 4.2.4 Single-strip framing camera data from 80 µm polyimide drive disk 62 4.2.5 Four-strip framing camera data . 64 4.3 Dual Radiographic Data . 66 4.4 Odd Radiographic Data . 72 4.5 Fringe Shifts from a Velocity Interferometry System for Any Reflector . 77 V. Radiographic Image Analysis ............................ 81 5.1 Shot-to-Shot Variability . 83 5.2 Shock Position as a Function of Time . 85 5.3 Shock Thickness as a Function of Time . 86 5.4 Structure in the Cooling Layer . 88 VI. Thomson Scattering Experiment in Argon Gas . 94 VII. Radiation Hydrodynamic Simulations . 110 7.1 One-Dimensional Hyades Simulations . 110 7.1.1 Production of a radiatively collapsed shock . 111 7.1.2 Drive disk thickness variation . 117 7.1.3 Late-time effects . 119 7.2 Two-Dimensional Simulations . 121 7.2.1 FCI . 122 7.2.2 Zeus . 123 7.3 Issues Between Simulation and Experiment . 126 7.4 One-Dimensional Simulations in Argon Gas . 132 7.5 Summary of Simulation Results . 135 VIII. Conclusions and Future Directions . 136 8.1 Radiative Shocks in Astrophysics . 137 8.1.1 Shocks Emerging from Supernovae . 138 8.1.2 Cooling of Stellar Atmospheres . 141 8.2 Applications . 146 8.3 Future Directions . 147 8.3.1 Flux Measurements . 147 8.3.2 Short-Pulse Backlighters and Ungated Imaging Diagnostics . 148 APPENDICES .......................................... 150 BIBLIOGRAPHY ........................................ 174 vi LIST OF FIGURES Figure 1.1 Hubble Space Telescope picture of the Cyngus Loop. False coloring shows different metal line emissions. Credit: NASA, HST, Jeff Hester. 4 1.2 Hubble Space Telescope image of SN 1987a, taken in 2003 with WFPC2. Here, a ring of circumstellar material lights up as the shockwave driven by the explosion heats it. Image credit: NASA and R. Kirshner. 5 1.3 Diagram of the planned laser facility at the Naval Research Laboratory in Wash- ington, D.C . 8 1.4 Outside of the NIF target chamber. Square protrusions are where bundles of four beams, called quads, will enter the target chamber. 9 1.5 Beampath of one of the NIF beams. 10 1.6 Cutaway schematic of the Z-machine’s latest upgrade, now referred to as Z-R. Implosions happen near the axis of this large cylinder. 11 2.1 Diagram of general structure of a collapsing radiative shock. After an initial tem- perature and density jump at the shock front, radiative cooling causes a decrease in electron temperature (which cools the ions collisionally), and a corresponding increase in density. The extent of this layer is dictated by energy balance of the sources of energy into and out of this transitional region, or “cooling layer”. 19 2.2 Radiation flow in a thick-thin shock. Radiation at the boundary between the optically thick upstream region and the transition region must be equal, and at must equal twice the flux from the transition region at the shock front on the other side of the transition region. 21 3.1 Photos of the University of Michigan Target Fabrication Center. a) System is mounted on an optics table in clean room to minimize dust and debris on op- tics and in stage mechanics. b) Two sets of coordinate systems aid holding and independently positioning two pieces during fabrication. 29 3.2 2D schematic of gas-filled target and 3D CAD drawing of target with attached backlighter foil. 31 3.3 (a) Metrology photo of target with area backlighter foil attached. Area backlighting is discussed further in section 3.3. (b) Metrology photo of gold grid attached to target. Note notches on the grid near the target body, that served as spatial indicators. Increasingly large notches were cut farther from the drive surface. (c) Metrology photo of target with no area backlighter attached. 32 vii 3.4 (a) Diagram of spherical target chamber at the Omega Laser facility. Numbered circles indicate beams, while larger circles numbered with H, P, and TIM labels are ports for both fixed and removable diagnostics. (b) Schematic of beam paths leading through charging banks and into the target chamber. Both images from the National Laser Users Facility User’s Guide. 34 3.5 Equivalent target plane images of beams spots integrated over a 1-ns pulse width. (a) An unsmoothed spot of a frequency-tripled Omega beam. (b) Beam spot smoothed with a continuous phase plate. (c) Beam spot smoothed with SSD. From the National Laser Users Facility User’s Guide. 35 3.6 Xenon transmission spectrum in the range of 3-8 keV and argon spectum in the range of 1-6 keV, as calculated for cold material. 38 3.7 Diagram of backlit pinhole backlighting setup, not to scale. In the Omega chamber, with the target at target chamber center, the backlighter target was 12 mm from the target axis, while the detector was 229 mm from the target axis on the opposite side, for an image magnification of 20. 40 3.8 Target schematic for pinhole backlighter target . Measured details for each target are filled in during fabrication and metrology. 41 3.9 Metrology photos of pinholebacklighter targets. a) Face-on view of backlighter target. The large rectangle is the 5 mm square tantalum substrate. The dark square seen is a feature on the tantalum, while close inspection shows the 2 mm polyimide square. The dotted-line crosshairs shown are features of the viewing system, and the center of the crosshair is positioned on the 20 µm pinhole. b) XTVS view of backlit pinhole target, imaged in metrology at same angle as one of the cameras on Omega when the target is correctly positioned. 42 3.10 Cartoon of framing camera components.