1. 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

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

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 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 Ultra Intense Laser Thin Foil e - Sheath Field H +, C +, C +2, … Ions TNSA Model d

6. How To Improve Conversion Efficiency 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. From the Solution to the Isothermal Model

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 = mass hydride /mass proton  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 Er+10 H f=0.40 H C+4 O+4 f=0.30 H C+6 O+8 f=0.21 LSP simulation shows for protons above 3MeV, erbium hydride improves conversion efficiency by 22% Time (ps) J/cm 2 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: ErH 3 - CHO Fully Ionized - CHO Ionized to +4 5μm Au-Er +10 3H + 5μm Au-C +6 H + O +8 5μm Au-C +4 H + O +4

9. Erbium Hydride Experiments Compared 3 Conditions:  Contaminants on foil  ErH 3 not cleaned (contaminant layer still present)  Cleaned ErH 3 5 or 14 micron Au substrate 200nm ErH3 40Å Oxide 10Å Contaminants Cleaned using Ar- ion Etcher ElementAtom % (a element ) Carbon50 Nitrogen1 Oxygen37 Fluorine1 Erbium11 X-ray Photoemission Measurement of Contaminant Composition Assume Contaminant Density of 1g/cc and Carbon and Oxygen from data are CH 2 and H 2 O. Proton Source Diameter ≈ 200μm. *  Approx. 1x10 12 Protons in Contaminants. * P. Patel, A. Mackinnon, M. Key, et al, Phys. Rev. Lett. 91, 125004 (2003). Estimation of the number of protons in contaminants Do these give the same result? Expected to Improve C.E. by factor of 1.22

10. Removing the Contaminant Layer Setup for Measuring the Etch Rate 45 deg 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. 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% * Callisto Type PackTitan Type Pack Titan: 5-7 cm from TCC Callisto: 2.5 cm to TCC Proton Beams are f/1 from flat foils Titan Pack Proton Range * D. S. Hey, Laser-Accelerated Proton Beams: Isochoric Heating and Conversion Efficiency. PhD thesis, University of California, Davis, 2007.

12. Calibration Curves Nikon Scanner Capable of Resolving Nearly 3 Orders of Optical Density RCF Dose Measurement www.nikonusa.com Super Coolscan™ 9000 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.www.srim.org RCF Exposed at CNL proton Cyclotron Scan of Step Wedge ND Filter

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

14. 14μm Gold Foil with Contaminants 3.8 MeV4.9 MeV5.9 MeV6.8 MeV 7.6 MeV8.3 MeV16.7 MeV22.1 MeV 26.7 MeV30.6 MeV34.2 MeV37.5 MeV 40.6 MeV Sample Fit (Un-Etched Gold) Energies computed from stopping powers determined using SRIM. (www.srim.org)www.srim.org

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 Carroll, D.C., et al. Central Laser Facility Annual Report 2005/1006 FBFBFBFB FEFEFEFE H+H+H+H+ C+C+C+C+ C +2 C +3 C +4

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

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

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

19. Callisto Hydride RCF Results (5μm Au) Improvement from Erbium Hydride is (25±19)% for protons above 3.4MeV From Contaminants C.E. = (0.12 ± 0.006)% From Erbium Hydride C.E. = (0.15 ± 0.016)% Au With Contaminants Au-ErH 3 Cleaned Raw DataProcessed Hole and off-edge represent 5% of dose

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

21. Preliminary Results for Titan TargetE Laser (J) # H + 10 12 C.E. > 3MeV Etched Au-ErH 3 1494.23.4% Un-Etched Au-ErH 3 1435.65.7% Un-Etched Au1373.02.5% Etched Au1360.60.3% 36% Cleaned Au-ErH 3 improvement in C.E. of 36%. 128% Au-ErH 3 improved C.E. by 128% !!! 10 12 Analysis of the contaminant layer suggests proton depletion at 10 12 protons More Shots Needed for Statistics!!! Preliminary

22. Affect of Etching Gold Light ions removed  Heavy ion acceleration efficiency improves * The gold was ionized up to +18,  Erbium has similar ionization potentials Calculated traces of ions plotted over data. Thomson Spectrometer Fujifilm™ IP with close-up look at Au ion signal Laser: 136 J at 0.5 ps, tight focus (f/3). Target: 14μm Au foil 3.8 MeV4.9 MeV5.9 MeV 6.8 MeV7.6 MeV8.3 MeV * 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, ErH 3 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-ErH 3 hopes to demonstrate a factor of 3 improvement this summer on Titan.

25. Extra Slides

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

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 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. Un-Etched Au Un-Etched Au-ErH 3

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

30. Affect of Ionization on Hydrides kT = 3MeVCarbonErbiumf(Er)/f(C) n e (cm -3 )Z avg Z max Z avg Z max From avgFrom max 1e193.3244.91131.281.24 1e203.6749.79161.261.18 1e213.62617.4311.091.11 1e225.09624.4401.140.91 1e235.15635.0530.910.69 1e243.48642.7580.620.63 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 ErH 3 with CH 2 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 Q 1.7, the ratio turns around.