Diagnostics for Benchmarking Experiments

L. Van Woerkom

The Ohio State University

University of California, San DiegoCenter for Energy Research

3rd MEETING FUSION SCIENCE CENTER

FOR EXTREME STATES OF MATTER AND FAST IGNITION PHYSICS

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

Why are Laser diagnostics important?

Proton production & focusing

Temperature of proton irradiated foil from XUV images

Size of proton irradiated region via XUV dominated by target geometry

Temperature strongly dependent on laser.Scatter in data probably due to laser

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Depth (µm)

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Why are target diagnostics important?

Current seems to drop quickly near front surface

mfp ~ 70 m

d

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

Diagnostics

• Laser Diagnostics– Develop in-situ peak intensity monitoring– Build robust high dynamic range autocorrelator– Build robust prepulse/pedestal system

• Target Diagnostics– Standard techniques

• K 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

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

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

Physics tells us about LaserPhysics tells us about Laser

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Intensity (Wcm-2)

Neon 1+ - 8+

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.

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.

Pulse Width Measurement

Pulse Characterization

Plasma shutter photodiode

target

3rd Order Autocorrelator w/ high dynamic range CCD camera

• 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

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

New Diagnostic Development

Chirped probe beam

Pump beam

Imaging spectrometer and polarization analyzer

camera

• Anomalous near-surface physics• Reflectivity & Polarization• Temporal & Spatial Mapping

• Surface conductivity• Magnetic fields

A. Benuzzi-Mounaix, M. Koenig, J. M. Boudenne, et al., Physical Review E 60, R2488 (1999).

Experimental Scenarios

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CCD

HOPG

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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 K imager– N Patel Cu K 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

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