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Diagnostics for Benchmarking Experiments

University of California, San Diego Center for Energy Research. Diagnostics for Benchmarking Experiments. 3rd MEETING FUSION SCIENCE CENTER FOR EXTREME STATES OF MATTER AND FAST IGNITION PHYSICS. L. Van Woerkom The Ohio State University. Overview.

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Diagnostics for Benchmarking Experiments

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  1. University of California, San Diego Center for Energy Research Diagnostics for Benchmarking Experiments 3rd MEETING FUSION SCIENCE CENTER FOR EXTREME STATES OF MATTER AND FAST IGNITION PHYSICS L. Van Woerkom The Ohio State University

  2. Overview • High level of activity in establishing Z-Petawatt • Laser still under construction • Z machine takes priority • 2 postdocs, 5 grad students over several months • Benchmarking  crucial to advance diagnostics • Laser diagnostics • Standard diagnostics • New techniques

  3. Why are Laser diagnostics important? Proton production & focusing Size of proton irradiated region via XUV  dominated by target geometry Temperature strongly dependent on laser. Scatter in data probably due to laser Temperature of proton irradiated foil from XUV images

  4. d Why are target diagnostics important? Current seems to drop quickly near front surface mfp ~ 70 mm • Big unresolved issues: • No agreement in theory • No agreement in codes • Inability of experiment to provide sufficient information to discriminate amongst them • Scale length on order of resolution • Diagnostics must improve

  5. Diagnostics • Laser Diagnostics • Develop in-situ peak intensity monitoring • Build robust high dynamic range autocorrelator • Build robust prepulse/pedestal system • Target Diagnostics • Standard techniques • Ka x-ray imaging  hot electrons • XUV imaging  temperature profile • HOPG spectra  temperature • Streaked XUV  temporal heating • New techniques • Time- and Space-resolved reflectivity • Time- and Space-resolved polarimetry • Space-resolved XUV spectroscopy

  6. Laser Diagnostic Development Goals • In-situ peak intensity monitor – • currently SNL • Directly measure intensity in focal region • Third order single-shot autocorrelator • design and building at OSU • Gives time direction • Gives pulse fidelity out to ~100 picoseconds • Pedestal measurement • design and building at OSU • Fast photodiodes • Plasma shutters for increased dynamic range

  7. Intensity calibration • Indirect method • Various laser parameters are measured outside the interaction region, from which peak intensity can be inferred • Direct (in situ) method • Based on measurement of intensity dependent phenomena at the interaction region, intensity at the focus can be ascertained

  8. Physics tells us about Laser We have a detailed understanding of high intensity laser atomic physics after two decades of extensive study. The laser has been used to understand the physics. Now, we use the physics to understand the laser. Neon 1+ - 8+ Highest charge states are well represented by current analytical atomic physics models and ratios of charge states from a single laser shot yield the peak focused laser intensity.

  9. Pulse Width Measurement • Making robust diagnostic tools, not reinventing the wheel • Taking advantage of many years of short pulse high intensity laser research • Along with the intensity measurement, this gives the actual experimental transfer function

  10. Improvements in Standard Techniques • Distinguishing models/codes requires improved resolution in space & time • Improving spatial resolution requires • Crystal manufacturing • Mirror alignment • Careful optical design • Improving temporal resolution • Streaked XUV • Streaked HOPG

  11. New Diagnostic Development Chirped probe beam Pump beam • Anomalous near-surface physics • Reflectivity & Polarization • Temporal & Spatial Mapping • Surface conductivity • Magnetic fields Imaging spectrometer and polarization analyzer camera A. Benuzzi-Mounaix, M. Koenig, J. M. Boudenne, et al., Physical Review E 60, R2488 (1999).

  12. Bragg crystal Bragg crystal CCD CCD HOPG Experimental Scenarios

  13. Who is doing what and where? • Supported fully or in part by the FSC • Core concentration at Sandia Z-Petawatt • J. Pasley  project coordinator • E Chowdhury  intensity measurement • D Offermann  intensity measurement & reflectivity • A Link  intensity measurement & Cu Ka imager • N Patel  Cu Ka imager • E. Shipton  optical interferometry • Support work at OSU • D Clark  HOPG design & construction • J Morrison  reflectivity development • V Ovchinnikov  reflectivity & deformable optics • XUV imaging spectrometer • A Link (will be in the UK over summer) • Data archiving and information • J Young, R Weber, K Highbarger, N Patel

  14. Summary & Conclusion Core efforts focused at Sandia Z-Petawatt • Advancing the understanding of FI requires • Robust, reliable, in-situ laser diagnostics • Improved spatial & temporal target resolution • Development of a new generation of high spatial & temporal diagnostic technologies

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