1. Lawrence Livermore National Laboratory Andrew G. MacPhee 17 th Topical Conference on High Temperature Plasma Diagnostics Albuquerque, NMWed 14 th May 2008 UCRL-PRES-403581 Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 Diagnostics for Fast Ignition Science

2. 2 Lawrence Livermore National Laboratory Collaborators F. Beg, T. Bartal, S. Chawla, T. Ma, J. King, J. Pasley, B. Westover, M.S. Wei R. Stephens, K. Akli L. D. Van Woerkom, R.R. Freeman, E. Chowdhury, D.W. Schumacher,D. Offermann, T. Link, V. Ovchinnikov C. Chen, M. Porkolab, MIT, USA Y.Y. Tsui, University of Alberta, Canada J. Bonlie, R. Coombs, H. Chen, M. Foord, S. P. Hatchett, D. Hey, A.J. Kemp, M. H. Key, A. B. Langdon, B. F. Lasinski, A. J. Mackinnon, B. Maddox, N. Izumi, H-S. Park, P. K. Patel, T.H.Phillips, D. Price, M. Tabak, R. Town

3. 3 Lawrence Livermore National Laboratory Density plot from 2D indirect drive fast ignition hydro design ~100  m For efficient burn with low driver energy 1.5 <  R<2 gcm -2 For high gain with low driver energy 300 <  < 500 gcm -3 Ignition 18 kJ in 23 ps,  =36  m, 1.1x10 20 Wcm -2 Laser intensity must reach several 10 20 Wcm -2 in ~20ps 1) How efficiently can we couple 1-3 MeV electrons to the imploded plasma? 2) How much pre-formed plasma can we tolerate? *M. Tabak, J. Hammer, M.E. Glinsky, et al, Phys. Plasmas 1, 1626 (1994); S. Atzeni, et. al, Phys. Plasmas 14, 052702 (2007) Fast Ignition*: Initiate burn prior to peak compression with an intense beam of energetic electrons  Integrated experiments on Omega-EP, NIF-ARC and FIREX will use neutron yield and fluorescence from tracers to measure efficiency and transport  Short pulse experiments on Titan allow diagnostics development, pre-pulse evaluation and code benchmarking

4. 4 Lawrence Livermore National Laboratory Scope of talk  On shot laser diagnostics at Titan  Electron energy deposition and transport  Measuring the hot electron spectrum

5. 5 Lawrence Livermore National Laboratory On shot diagnostics are an essential record for modeling experiments 6m lens 150J 0.6ps, 1  from pulse compressor Initial set-up microscope Interferometer 2 , 1ps, 10mJ probe beam Full aperture retro-focus system Pre-pulse monitor ` ` Equivalent plane monitor

6. 6 Lawrence Livermore National Laboratory The pre-pulse monitor is vital for modeling laser target interaction SF ~ 5 mJ Spike ~ 2.5 mJ -3 ns -0.1 ns Time (ns) 0 5 -5 * Ying Tsui, University of Alberta MinTypicalMax ~3ns superfluorescence 0.3mJ5mJ70mJ ~1ps pre-pulse1mJ2.5mJ30mJ (at 1.4ns, <Feb) Combined energy contrast vs main pulse 10 5 2x10 4 1.5x10 3

7. 7 Lawrence Livermore National Laboratory Electron density from interferograms agree well with 2D hydro using pre-pulse data 150J, 2ps shot on 25  m aluminum foil: 70 mJ SF + 30 mJ spike N e (cm -3 ) (+)n e interferogram data (-------)n e simulation: 100 mJ SF only (-------)n e simulation: 70 mJ SF + 30 mJ spike Density plateau due to spike 10 17 10 18 10 19 10 20 10 21 10 22 0 50100 150 200250 Z(um) Castor2 simulation with U of A EOS for Al: Interferogram: Together, interferometry and pre-pulse measurements let us benchmark hydro codes * Ying Tsui, U of A, ** Sebastian Le Pape LLNL

8. 8 Lawrence Livermore National Laboratory There is good agreement between equivalent plane images for system shots and the low power alignment pulse System shot #02042408 Low power (OPCPA) alignment pulse Binned lineouts through both spots: Full shot Fraction of power above given intensity: 50% >4x10 19 20% >10 20 Low power (scaled) Full shot Low power (scaled)

9. 9 Lawrence Livermore National Laboratory These experiments rely on k-  fluorescence for measuring coupling efficiency and Bremsstrahlung spectra for measuring T hot Thin front Al layer: No laser excitation of Cu k-  Titan Laser 150J, 0.6ps, ~10 20 Wcm -2 Thick rear Al layer: Electrons make only one pass through Cu tracer Cu fluor layer: k-  fluorescence measures hot electron yield e-e- e-e- e-e- Bremsstrahlung + k- 

10. 10 Lawrence Livermore National Laboratory Multiple diagnostics on Titan are used to characterize energy deposition, conversion efficiency and the hot electron spectrum K-  crystal imager axis Hot e - spatial distribution XUV multilayer imager axis Temperature map Specular reflection Single hit CCD Calibrates… Signal (Ph/J/Sr/eV) Energy (keV) …absolute K-  yield from HOPG crystal spectrometer T hot diagnostic Long pulse beam introduces controlled pre-pulse Main pulse ~140J 600fs ~10 20 Wcm -2

11. 11 Lawrence Livermore National Laboratory The reflection of laser light from oblique targets is important for coupling in cones* K-  image Ray-trace Laser bounce *Tony Link, OSU, HELDA 2008 Grazing angle Reflectivity (%) Power on target (TW) 621.8193 155420 155255 1539190 Cu foil target Spectralon™ plate Laser incident at angle  to target surface  Image recorded on 16bit CCD  Laser light reflected from cone wall can provide useful energy at the tip  Reflection at 75º to normal ~20x reflection at 28º  S and P have similar reflectivity at 75º  f/3 incident beam scatters ~diffusely into a f/2 cone of rays

12. 12 Lawrence Livermore National Laboratory XUV images measure the black body temperature at the rear surface of the target* T e from 256eV channel T e from 68eV channel Ultra intense laser-target interactions create MeV electrons Planckian emission from rear surface peaks in the XUV Temperature corresponds to Lasnex 2d rad. hydro run with matching integrated XUV signal within mirror bandwidth Used to constrain hybrid PIC codes Filter Laser: 1  m, 150J 0.6ps, ~10 20 Wcm -2 Back illuminated CCD Spherical XUV multilayer mirror Plane XUV mirror 25  m CD target image at 256eV Tight focus peak intensity 10 20 Wcm -2 *Tammy Ma, These proceedings (B15)

13. 13 Lawrence Livermore National Laboratory A spherically bent crystal imager is used to measure the k-  source size Crystal imager for Cu K-  radiation: 5eV bandwidth, 10x magnification, 20  m resolution => hot electron source size Line shift due to ionization of low Z Cu tracer limits crystal imager effectiveness for hot plasmas * For higher opacity integrated experiments a 16keV imager (Zr K-  ) is being developed that if successful will be less sensitive to line shift Spherically bent quartz (211) 30  m Cu foil, 500  m x 500  m ~5.10 18 Wcm -2 500  m Cu foil target Laser 2d: 3.082Å,  B @ n=2, 8.04keV=1.31° J.A. Koch et al., Rev. Sci. Instrum. 74, 2130 (2003), *K.U. Akli, Phys. Plasmas 14, 023102 (2007), Image plate or CCD ~60  m FWHM

14. 14 Lawrence Livermore National Laboratory ~12  m Ag target Laser 20  m Pd 30  m Mo Image plate 6x6 Ta pinhole array 30  m , 500  m thk Pd Filter Mo Filter Contrast K  / Brem: ~1.4 Signal to background: ~6:1 Absolute calibration is in progress Pinhole limited width <30  m A pinhole camera with Ross pair filtering is insensitive to k-  line shift in hot plasmas

15. 15 Lawrence Livermore National Laboratory K-  imaging and Lasnex modeling show pre-pulse in cones is a significant issue 15mJ 2ns ncnc 300  m 1e18 5e21 60  m Density on axis Lasnex hydro of pre-pulse plasma: See also Sophie Baton, LULI, submitted to POP ~80% K-  yield within 200  m of tip 750  m n c @ 60  m ~80% deposited within 200  m` Cu K-  image Titan: 15mJ pre-pulse 4.5J 300ps 1e22 1e15 2e19 300  m ncnc 80  m n c at 80  m, n e ~10 19 at 300  m Titan: ~1J pre-pulse n c @ 80  m <20% deposited within 200  m` <20% K-  yield within 200  m of tip Anticipated NIF-ARC scale pre-pulse Cu K-  image

16. 16 Lawrence Livermore National Laboratory A HOPG crystal spectrometer measures the absolute K-  yield produced by hot electrons in the buried tracer layer crystal Image Plate Direct Block TCC 9758 eV HOPG spectrometer *K. Akli, GA, These proceedings k-  signal from HOPG normalized against single hit CCD averaged over several shots Cu k-  8keV Cu k-  8.9keV

17. 17 Lawrence Livermore National Laboratory Single hit CCD provides absolute calibration for HOPG ~20% error in ccd efficiency  CCD ~10% error in single event determination Filter Tx × solid angle ×  CCD × Laser energy k-  event counts k  yield = Single events recorded at CCD plane Histogram of single events = X-ray spectrum Zoom Cu k-  k- 

18. 18 Lawrence Livermore National Laboratory An absolutely calibrated Bremsstrahlung spectrometer is used to measure the hot electron spectrum* e-e- Dosimeters (Image Plates or TLD’s) Collimator Electron Spectrometer Pb + plastic housing Sensitive from 10-400keV X-rays Vacuum electron spectrometer removes charges particles from line of sight. Sensitive from 0.1-4 MeV electrons** *R. Nolte et al, Rad. Prot. Dosim., (1999); C. Chen, These proceedings (B3) **H. Chen These proceedings (D37)

19. 19 Lawrence Livermore National Laboratory Spectrometer Response matrix (modeled: ITS) Target Response matrix (modeled: ITS) h e-e- … Al Ti Fe Cu IP 1IP 4 … Pb … IP 13 … Recorded signal Deconvolved electron spectrum inside target The hot electron spectrum is deconvolved from the bremsstrahlung spectrum using the Monte Carlo code ITS* 30° full angle 8  m diam. source Vary I, T minimize SD vs dosimeters *C. Chen, These proceedings (B3)

20. 20 Lawrence Livermore National Laboratory A 1-T Boltzmann distribution provides a good fit to the measured data * *C. Chen, These proceedings (B3) One temperature fit: (1.3±0.15) MeV using ITS Monte Carlo model 8% conversion (~10J) to 1-3MeV electrons from ITS using Brem. 15% conversion to 1-3MeV electrons from ITS using absolute K-  yield Estimate based on K-  yield is more sensitive to lower energy electrons 121J, 10 20 Wcm -2 Non-refluxing Cu foil target  Next step: 2 Temperature fit, hybrid PIC simulations to include ohmic potentials, return currents, resistivity  conversion efficiency may drop MeV/mm 2 Dosimeter layer

21. 21 Lawrence Livermore National Laboratory This 1 temperature analysis using ITS shows that T hot scales with intensity at a lower rate than suggested by pondermotive scaling Beg scaling: T hot (MeV)= 0.1(I 2 /(10 17 W/cm 2  m 2 )) 1/3 Pondermotive scaling: T hot (MeV)= (I 2 /(10 19 W/cm 2  m 2 )) 1/2

22. 22 Lawrence Livermore National Laboratory Summary On shot laser diagnostics are crucial for benchmarking simulations: Interferometry agrees with 2D hydro for foil targets using the measured pre-pulse Equivalent Plane imaging demonstrates consistent intensity distribution between the Titan alignment beam and full system shots The 1-T hot electron spectrum analysis shows less than pondermotive scaling We need to include hybrid PIC simulations and a 2-T model to better understand both conversion efficiency and the electron energy spectrum

23. 23 Lawrence Livermore National Laboratory Backup slides

24. 24 Lawrence Livermore National Laboratory XUV spectroscopy measurements give a lower bound on black body imaging results* 45° *Tammy Ma, These proceedings (B15) Intensity ratio Front (plume) Rear (surface) Gold coated cylindrical mirror Harada grating CD Target Measured line ratios agree with synthetic spectra at given T, 

25. 25 Lawrence Livermore National Laboratory... 92-100 MeV 1-1.1 keV 13 89-100 MeV 0-5 keV 92-100 MeV 1-1.1 keV C 1,1 C 1,2 C 1,3... C 1,150 C 2,1 C 3,1 C 13,1 C 13,150... C 2,2... 1 2 3 Energy per photon deposited in each IP T 1,1 T 1,2 T 1,3... T 1,80 T 2,1 T 3,1 T 150,1 T 150,80... T 2,2... Number of photons generated per e - = × × Target response matrix: ITS 150 photon energy bins × 80 electron energy bins... Cannon response matrix: ITS 13 Image Plate Layers × 150 photon energy bins Image plate signal: 13 dosimeter readings Electron spectrum: 80 electron energy bins N1N1 N2N2 N3N3 N 80... D1D1 D2D2 D3D3 D 13... Vary I, T minimize SD vs dosimeters Bremsstrahlung analysis

26. 26 Lawrence Livermore National Laboratory multiple pass-refluxing Cones have the highest yield Single pass Oblique incidence *K. Akli, GA, These proceedings Absolute yield depends on target and laser configuration

27. 27 Lawrence Livermore National Laboratory Tight focus at tip Focus Down-stream 800  m Focus Down-stream 400  m Focus Up-stream 400  m 68eV XUV channel ~8keV Cu K-  channel Ray-trace aberrated Titan beam ~100  m tight and 400  m defocus k-  peak Best focus ~1.1MeV 800  m defocus ~0.25MeV 400  m defocus ~0.4MeV n c at ~40  m (from hydro) ~155  m 800  m defocus k-  peak XUV poster GP8.00065: Tammy Ma FoilCone:  T hot :~1MeV1.1MeV  k-  yield:7x10 9 Ph/J/Sr 2.5x10 10 Ph/J/Sr Efficiency~50% ~140  m to tip ~200  m to tip ~180  m to tip XUV and K-  imaging are used to measure coupling and transport in cones S Baton LULI, LVW OSU POP