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Dustin Offermann Graduate Research Associate Department of Physics The Ohio State University

Proton Conversion Efficiency Using Erbium Hydride Coatings Interview for Postdoctoral Research Position at Sandia National Laboratory. Dustin Offermann Graduate Research Associate Department of Physics The Ohio State University Columbus, Ohio 43210. People and Acknowledgements.

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Dustin Offermann Graduate Research Associate Department of Physics The Ohio State University

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  1. Proton Conversion Efficiency Using Erbium Hydride CoatingsInterview for Postdoctoral Research Position at Sandia National Laboratory Dustin Offermann Graduate Research Associate Department of Physics The Ohio State University Columbus, Ohio 43210

  2. People and Acknowledgements The Ohio State University - L.D. Van Woerkom, R.R. Freeman, E. Chowdhury, A. Link, D.T. Offermann, V. Ovchinnikov Lawrence Livermore National Laboratory - M. Key, A. Mackinnon, P. Patel, A. MacPhee, Y. Ping, J. Sanchez, N. Shen, H. Chen, M. Foord, W. Unites, D. Hey University of California, San Diego - F. Beg, T. Bartal, J. King, T. Ma, S. Chawla Massachusetts Institute of Technology - C. Chen General Atomics - R. Stephens, K. Akli University of Alberta - Y. Tsui This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Sandia National Laboratory - L. Espada

  3. About Me • Degrees • BS in Physics, Seattle University, Seattle, WA, 2002 • MS in Physics, The Ohio State University, Columbus, OH, 2005 • PhD in Physics (pending), The Ohio State University, Columbus, OH • Graduate Research Experience • The Ohio State University, LVW Short Pulse Laser Lab • Ti:Sapphire CPA laser system (1TW) • Multi-photon ionization experiments • Sandia National Laboratory, ZBL 100TW • Experiments in Collaboration with Sandia, UCSD and Ohio State • Lawrence Livermore National Laboratory, JLF Callisto and Titan Lasers • Proton Conversion Efficiency Experiments • Support for Numerous Titan and Callisto experiments

  4. Jupiter Laser Facility Website Me

  5. Motivation H+, C+, C+2, … Ions d e- Sheath Field Ultra Intense Laser H+, C+, C+2, … Ions Thin Foil TNSA Model • Proton Fast Ignition Requires * (Fuel Density 400g/cc, d=1mm) • Protons Focus to a 30μm Diameter Spot • Slope Temperature ≈ 3MeV • For These Parameters an Enclosed Geometry is Needed • Total Beam Energy of 15kJ • (15% Conversion Efficiency for 100kJ Laser) * S. Atzeni, M. Temporal, J.J. Honrubia, Nucl. Fusion 42 (2002) L1–L4

  6. How To Improve Conversion Efficiency From the Solution to the Isothermal Model • Better Conversion to Hot Electrons • Optimization of Laser Conditions (Pre-pulse, etc) • Target Materials with Good Coupling • Thin Foils • Experiments Show 1/L Scaling • Requires Very Low Pre-Pulse • Coated Rear Surfaces • More Protons Available • More Protons per Non-Hydrogen Atom • If Non-Hydrogen Atoms are High Mass Then the Fraction of Energy Carried by the Protons Will be Greater * P. Mora, Phys. Rev. Lett. 90, 185002 2003. * P. Mora, Phys. Rev. E 72, 056401 2005. ** E. A. Williams et al., Phys. Plasmas 2, 129, 1995.

  7. Theory and Motivation • LSP model show for high-Z hydrides like Er and U, conversion efficiency to protons approaches that of pure hydrogen. • Semi-empirical model from the simulated data, where • M = masshydride/massproton • N = # of protons per hydride • Q = Charge of hydirde Experiments Seek to Observe This Region Contaminants M. Foord, A. Mackinnon, P. Patel, et al, J. Appl. Phys. 103, 056106 (2008).

  8. LSP Model of Callisto Targets • LSP simulations were run until total ion energies vs run time became asymptotic. • The number f is the fraction of beam energy in protons above 3MeV • Three cases are shown: ErH3 - CHO Fully Ionized - CHO Ionized to +4 f=0.21 H H H f=0.30 f=0.40 C+6 C+4 J/cm2 J/cm2 J/cm2 O+8 O+4 Er+10 Time (ps) Time (ps) Time (ps) 5μm Au-Er+10 3H+ 5μm Au-C+6H+O+8 5μm Au-C+4H+O+4 LSP simulation shows for protons above 3MeV, erbium hydride improves conversion efficiency by 22%

  9. Erbium Hydride Experiments X-ray Photoemission Measurement of Contaminant Composition • Compared 3 Conditions: • Contaminants on foil • ErH3 not cleaned (contaminant layer still present) • Cleaned ErH3 Do these give the same result? Expected to Improve C.E. by factor of 1.22 Estimation of the number of protons in contaminants 5 or 14 micron Au substrate 200nm ErH3 40Å Oxide 10Å Contaminants Cleaned using Ar-ion Etcher • Assume Contaminant Density of 1g/cc and Carbon and Oxygen from data are CH2 and H2O. • Proton Source Diameter ≈ 200μm. * •  Approx. 1x1012 Protons in Contaminants. * P. Patel, A. Mackinnon, M. Key, et al, Phys. Rev. Lett. 91, 125004 (2003).

  10. 45 deg Removing the Contaminant Layer Argon Ion Sputtering Gun Etching System • Positioned 15cm behind TCC and inclined 45 degrees in Callisto. • Positioned 15cm behind TCC and inclined 39 degrees in Titan. • Etcher beam diameter approx 3cm. • Hydride thickness reduction rate measured to be ~15nm/min. Setup for Measuring the Etch Rate Microprofilometer Scan Removes 15 nm per min Scan Length (μm)

  11. Radiochromic Film Pack (Primary Diagnostic) • Purpose: RCF packs are the tried and tested means to measure proton conversion efficiency, slope temperature, and beam properties. • Energy Range: from 3.8 to 40 MeV • Typical Dose: up to ~180 krad • Dose Uncertainty: 20% * Titan: 5-7 cm from TCC Callisto: 2.5 cm to TCC Proton Beams are f/1 from flat foils Titan Pack Proton Range Callisto Type Pack Titan Type Pack * D. S. Hey, Laser-Accelerated Proton Beams: Isochoric Heating and Conversion Efficiency. PhD thesis, University of California, Davis, 2007.

  12. Scan of Step Wedge ND Filter Calibration Curves RCF Dose Measurement www.nikonusa.com Super Coolscan™ 9000 RCF Exposed at CNL proton Cyclotron • Nikon Scanner Capable of Resolving Nearly 3 Orders of Optical Density • Film was calibrated using a 64.5MeV proton beam from the Crocker Nuclear Laboratory Cyclotron at University of California, Davis. • The Absorbed Energy was Computed From SRIM (www.srim.org) Stopping Powers.

  13. Rippled 25μm Cu with CH Coating  to RCF Virtual Source Ripple Surface Target • Ripples on Cu-CH (3μm Repeat) made by General Atomics • 12th layer film  34.5 MeV •  approx 125μm source diameter

  14. 14μm Gold Foil with Contaminants Sample Fit (Un-Etched Gold) 3.8 MeV 4.9 MeV 5.9 MeV 6.8 MeV 7.6 MeV 8.3 MeV 16.7 MeV 22.1 MeV 26.7 MeV 30.6 MeV 34.2 MeV 37.5 MeV Energies computed from stopping powers determined using SRIM. (www.srim.org) 40.6 MeV

  15. Thomson Spectrometer • Distance to TCC – 13/37 cm (Callisto/Titan) • View - Target Rear Normal • Voltage -4000 V • Peak Magnetic Field - 6.0 kGauss • Pinhole Diameter - 250/200 microns • Minimum Proton Energy - 1.0 MeV • Detector - BAS-TR/SR image plate FB C+3 C+4 C+2 H+ C+ FE Carroll, D.C., et al. Central Laser Facility Annual Report 2005/1006

  16. Callisto Laser http://jlf.llnl.gov

  17. Thomson Spectrometer 13cm RCF 2.5cm Probe 400nm Imaging Lens to Interferometer 800nm 28° To Single Hit Experimental Setup Thomson Spectrometer (Callisto 13cm from TCC Titan: 36.7cm from TCC) RCF (Callisto: 25mm from TCC Titan: 65mm from TCC) TCC Diagnostics • Radiochromic Film Pack • Thomson Spectrometer • Side-on Interferometer • Single Hit CCD

  18. Callisto Thomson Data • Contaminants show H+ and C+4 as the dominant ions • LSP simulations with this assumption predict a 22% increase in proton C.E. Contaminants NOT removed Without ErH3 With ErH3 Cleaned ErH3 Target C+4 C+4 C+5 H+ C+5 H+ C+4 C+5 H+ C+3 C+3 C+3 C+2 C+2 C+2 C+ C+ C+ Bright lines are H+ and some C+5 Bright lines are C+4 and H+

  19. Callisto Hydride RCF Results (5μm Au) Hole and off-edge represent 5% of dose • From Contaminants • C.E. = (0.12 ± 0.006)% • From Erbium Hydride • C.E. = (0.15 ± 0.016)% Raw Data Processed Au With Contaminants Au-ErH3 Cleaned Improvement from Erbium Hydride is (25±19)% for protons above 3.4MeV

  20. Titan Laser http://jlf.llnl.gov

  21. Preliminary Results for Titan Preliminary • Cleaned Au-ErH3 improvement in C.E. of 36%. • Au-ErH3 improved C.E. by 128%!!! • Analysis of the contaminant layer suggests proton depletion at 1012protons • More Shots Needed for Statistics!!!

  22. 3.8 MeV 4.9 MeV 5.9 MeV 6.8 MeV 7.6 MeV 8.3 MeV Affect of Etching Gold Laser: 136 J at 0.5 ps, tight focus (f/3). Target:14μm Au foil • Light ions removed  Heavy ion acceleration efficiency improves * • The gold was ionized up to +18,  Erbium has similar ionization potentials Thomson Spectrometer Fujifilm™ IP with close-up look at Au ion signal Calculated traces of ions plotted over data. * M. Hegelich, S. Karsch, et al., Phys. Rev. Lett. 89, 085002 (2002).

  23. Conclusion • Erbium hydride DOES improve conversion efficiency. • In Callisto the mechanism is that of the model predicted by LSP simulations from Mark Foord, et al. • In Titan, depletion of hydrogen in the contaminant layer is the likely explanation.

  24. Future Efforts • Though results from this experiment do not reach the goal of 15% conversion efficiency, 5.7% offers hope • With a density of 7.6g/cc, ErH3 targets can be made thinner than CH and still provide enough hydrogen to avoid depletion • A study of laser pulse length effects with 5μm Au-ErH3 hopes to demonstrate a factor of 3 improvement this summer on Titan.

  25. Extra Slides

  26. Titan Thomson Data Contaminants NOT removed Without ErH3 With ErH3 Cleaned ErH3 Target C+3 C+4 C+3 C+4 C+3 C+4 C+2 C+2 C+2 H+ H+ H+ C+ C+ C+ Multiple sources due to edge effects

  27. Single Hit • Single hit spectra for the 5 Titan shots on gold are each similar in yield. • Black inverted line is a copper spectrum for reference.

  28. Probe Un-Etched Au-ErH3 Un-Etched Au • Because of curled edges on the target, most probe data was obscured on several shots. • These two shots are the exception, however self-emission was also too bright.

  29. Converting Pixel Values to Dose • Box and Whiskers show pixel values from data • Curves are the calibrated film response First 6 layers of film 7th-14th Layer 15th Layer HD810 MD v2 55

  30. Affect of Ionization on Hydrides • As the electron density goes up, the electric field strength goes up. • Ionization by Barrier Suppression is the dominant ionization mechanism. • Erbium can easily ionize to higher charge states than Carbon and because of the Q1.7, the ratio turns around. Table showing how the ratio of proton conversion efficiency changes as the sheath E-field increases with the root of the hot electron density. Here I compare ErH3 with CH2

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