Three-Dimensional Characterization of Cryogenic Target Ice Layers Using Multiple Shadowgraph Views

Abstract Backlit optical shadowgraphy is the primary diagnostic for D2 ice layer characterization of cryogenic targets for the OMEGA Laser System at the Laboratory for Laser Energetics (LLE). Reflection and refraction of light passing through the ice layer produce characteristic rings. The position of the most prominent of the shadowgraph rings, known as the bright ring, can be resolved to ∼0.1-pixel rms, corresponding to about 0.12 μm for typical LLE target shadowgraphs. Measurement of the bright ring position in conjunction with ray-trace model predictions determines the ice layer thickness and the Fourier-mode spectrum of the ice roughness for that view. The LLE target characterization stations use two camera angles and target rotation to record target shadowgraphs from many different views. Combining these views allows construction of a 3-D ice layer representation, an estimation of the global surface roughness, and a determination of a Legendre-mode spectrum suitable for implosion modeling. The standard operating procedure is to construct a 3-D ice layer representation using the analysis of 48 separate shadowgraphic views. The 3-D ice surface is then decomposed in terms of spherical harmonics, allowing the determination of low-mode number (ℓ ≤ to 10) elements of a Legendre-mode power spectrum. Higher-mode number elements of the Legendre power spectrum are determined by mapping the Fourier-mode power spectrum averaged over all views

[1]  D. Meyerhofer.  1991 Summer research program for high school juniors at the University of Rochester's Laboratory for Laser Energetics , 1991 .

[2]  G. J. Borse,et al.  Numerical Methods with MATLAB: A Resource for Scientists and Engineers , 1996 .

[3]  Gilbert W. Collins,et al.  Numerical Raytrace Verification of Optical Diagnostics of Ice Surface Roughness for Inertial Confinement Fusion Experiments , 2003 .

[4]  R. Town,et al.  Analysis of a direct-drive ignition capsule designed for the National Ignition Facility , 2001 .

[5]  R. Town,et al.  Core performance and mix in direct-drive spherical implosions with high uniformity , 2001 .

[6]  Samuel A. Letzring,et al.  Initial performance results of the OMEGA laser system , 1997 .

[7]  D. N. Bittner,et al.  Demonstration of Symmetry Control of Infrared Heated Deuterium Layers in Hohlraums , 2004 .

[8]  Jane Gibson,et al.  Complete Surface Mapping of ICF Shells , 2003 .

[9]  E. Mapoles,et al.  High-Resolution Optical Measurements of Surface Roughness for Beta-Layered Deuterium-Tritium Solid Inside a Re-Entrant Copper Cylinder , 1996 .

[10]  E. Mapoles,et al.  Surface roughness measurements of beta-layered solid deuterium-tritium in toroidal geometries , 1996 .

[11]  S. Pollaine,et al.  Characterizing spherical harmonic coefficients on an ICF capsule , 2004 .

[12]  J. Pipes,et al.  Cryogenic D-T fuel layers formed in 1 mm spheres by beta-layering , 1997 .

[13]  Stephan A. Letts,et al.  Forming uniform HD layers in shells using infrared radiation , 1998 .

[14]  William J. Hogan,et al.  The National Ignition Facility , 2001 .

[15]  Jeffrey A. Koch,et al.  Quantitative Analysis of Backlit Shadowgraphy as a Diagnostic of Hydrogen Ice Surface Quality in ICF Capsules , 2000 .