26 February 2015 A robust in-situ warp-correction algorithm for VISAR streak camera data at the National Ignition Facility
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The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is a 192-beam pulsed laser system for high energy density physics experiments. Sophisticated diagnostics have been designed around key performance metrics to achieve ignition. The Velocity Interferometer System for Any Reflector (VISAR) is the primary diagnostic for measuring the timing of shocks induced into an ignition capsule. The VISAR system utilizes three streak cameras; these streak cameras are inherently nonlinear and require warp corrections to remove these nonlinear effects. A detailed calibration procedure has been developed with National Security Technologies (NSTec) and applied to the camera correction analysis in production. However, the camera nonlinearities drift over time affecting the performance of this method. An in-situ fiber array is used to inject a comb of pulses to generate a calibration correction in order to meet the timing accuracy requirements of VISAR. We develop a robust algorithm for the analysis of the comb calibration images to generate the warp correction that is then applied to the data images. Our algorithm utilizes the method of thin-plate splines (TPS) to model the complex nonlinear distortions in the streak camera data. In this paper, we focus on the theory and implementation of the TPS warp-correction algorithm for the use in a production environment.
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George R. Labaria, George R. Labaria, Abbie L. Warrick, Abbie L. Warrick, Peter M. Celliers, Peter M. Celliers, Daniel H. Kalantar, Daniel H. Kalantar, "A robust in-situ warp-correction algorithm for VISAR streak camera data at the National Ignition Facility", Proc. SPIE 9345, High Power Lasers for Fusion Research III, 93450Q (26 February 2015); doi: 10.1117/12.2085127; https://doi.org/10.1117/12.2085127

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