Electron Transport Experiments

1. Electron Transport Experiments Farhat Beg RAC FSC Fusion Science Center Meeting Feb. 28, 2007

2. Lawrence Livermore National Laboratory Collaborators J. Pasley, Mingsheng Wei, J.King, Tammy Ma, Erik Shipton R. Stephens R.R. Freeman, L.Van Woerkom, D. Offerman, K. Highbarger, R. Weber M. H. Key, A.J. MacKinnon, A. MacPhee, S. Lepape, P. Patel, S. Wilks D. Hey P.A. Norreys K. Lancaster, J. S. Green H. Habara, R. Kodama

3. Progress So Far Two sets of experiments on electron transport • Nail and wire targets • Warm dense targets Status: • Analysis of the results is in progress • Four weeks in summer have been allocated on Titan laser for FSC experiment (two weeks each for UCSD and OSU)

4. New targets were developed 50 µm dia Ti wire (only on Titan) 1 mm to bend 100 µm dia head 20 µm dia wire 1 mm to bend Rationale for wire/nail targets: • Simple - no glue, simple geometry • Large head so laser can reliably hit it • Accessible to diagnostics • Small - completely simulate Status: • Experiments have been performed on both the Vulcan PW at RAL and the Titan laser at LLNL • Experiments have been modeled using three codes, i.e., LSP, e-PLAS and PICLS Data analysis is in progress

5. Laser Parameters and Diagnostics Setup Vulcan Laser at RAL • Energy ~ 500 J • Pulse length ~ 1 ps • Spot size ~ 10 µm • Intensity ~ 6x1020 Wcm-2 Titan Laser at LLNL • Energy ~ 100 J • Pulse length ~ 500 fs • Spot size ~ 15 µm • Intensity ~ 1x1020 Wcm-2 • Imaging • XUV - 68, 256 ev • X-ray - 4.5, 8.0 keV 45O

6. Initial fall-off is rather rapid: 1/e <200 m Cu Kimages Nail head 100 µm Laser 1 mm • Initial 1/e decay length is very similar for cone and nail head targets • Small fraction has very long path length - very visible in cone-wire target

7. XUV - 68 eV 20060809s2 Extended heating seen in XUV images - mostly return current Laser Jet • Hydro jets at every inside edge • Non uniform emission along the wire • Low level heating for entire length of wire • Hotter for ~200 mm - associated with hot electrons Jets Jet X-ray emission from 1 ps laser heated wire 1 mm F. N. Beg et al., PRL 92, 095001 (2004) • Data being analysed to obtain temperature

8. Evidence of Surface Heating from 256 eV images • The nail head and wire exhibits limb brightening • mass thickness ~ 0.04 m • Physical thickness ~ 1 m • Surface current - is it from hot electrons?? jet XUV - 256 eV 20060809s2 20 µm

9. Modified targets were used to study surface current on Titan laser 100 µm • 20 micron Cu wire is coated with 2microns of Ti • Simultaneous radiography shows surface and core current • similar decay length • Current through the wire 100 µm 8.0keV Actual target 4.5keV Quantitative analysis of current partition between surface and bulk is underway

10. Kalpha emission has been observed even after 900 bend Back of wire Front of wire 660um Surface current with extremely long propagation range! Limb brightening after the bend

11. 1 mm Cone-wire targets are much different in XUV • XUV (256 eV) images show emission from the large area inside the cone • Emission was also observed near the tip of the cone • XUV emission was not observed from the wire glue 256 eV K LPI inside the cone is an interesting issue for the advanced Fast Ignition

12. Initial analysis shows change in propagation length with laser energy • Both Titanium coated copper nail and bare Ti wire have similar 1/e lengths Cu Kalpha-8 keV Ti Kalpha-4.5 keV

13. SUMMARY • Three different targets were used • Surface transport is noticeable in nail/wire • Energy localization in all three targets? • Ground connection causes more heating in nail/wire targets • Future Work • Measurement of E & B field to better characterize currents • Improvement in modeling for benchmarking

14. Motivation for Electron Transport in Hot Dense Matter Cone guided FI DT FI • Most experiments are performed far from FI conditions • Electron transport in hot targets is different

15. Shock Heated Targets • Shock heated • Long pulse accelerates pusher plate • Compresses & heats foam • Short pulse laser interacts with gold • Hot electrons produced are detected by copper plate • Measures electron transport into plasma • Mimics the cone tip shock interaction

16. 60 6 Foam 30 3 r, g/cc Au Temp, eV Cu 00 0 0.15 0.18 0.17 0.16 depth, mm Shock driven experiment shows foam compression to 1 g/cc gold Density, g/cc Temperature, eV Radiograph • Long pulse accelerates Al/Cu flyer plate • Compresses foam to ~1 g/cc • Shock wave penetrates Au foil on opposite side • Electrons generated in Au cross the Au/interface and are counted in Cu

17. Various types of targets were used to understand transport • Au/Cu/Al - measure electron generation in Au • short pulse laser, Cu-Ka imager, single hit CCD and spectrometer • Au/CRF/Cu/Al - measure losses in hot foam • Long pulse, check timing w backlight • Long & short pulse, Cu-Ka imager, single hit CCD and spectrometer • Au/CH/Cu/Al - measure losses in cold CH, same areal density • Long & short pulse, back-light, Cu-Ka imager and spectrometer Aim was to produce large enough plasma to diagnose

18. Target Schematic Real target Is actually rectangular for cone glue • A variety of diagnostics was used

19. X-ray backlit images show shocked compression of foam #5 18th Sept #3 18th Sept 0ns 3.5ns 300 LPI mesh Resolution 24 microns h2d 5.6ns gold Shock 55 µm into foam Bremsstrahlung from long pulse interaction. #5 14th Sept #4 13th Sept 5ns 7ns • Radiographs show • shocked compressed • foam between copper • and gold surface • Good agreement with 2D rad-hydro simulations Shock 90 µm into foam 200J @ 2,200m spot,2ns

20. Shock heated targets • Timing of short pulse varied with respect to long pulse to examine transport through: - Cold Au/shocked foam - Cold Au /partially shocked foam - Shocked Au /shocked foam

21. Target composition affects the electron transport Al/Cu/Au 10ps Al/Cu/CH/Au, 1ps Hea1,2 Ka Hea1,2 Kb Ka Ka Lya Kb Lya Kb Shot 4, 6th September, 140J Shot 2, 6th Sept, 256J Shot 2, 7th September, 152J • Presence of He shows heating of copper for both 1 and 10 ps laser pulses • He disappears with an addition of CH in the target • Transport is significantly different in insulator targets • More accurate information from a single CCD camera CPA 5m Au 5m Cu 20m Al

22. Fully shocked target shows reduction in Cu Kalpha Ka Ka Kb Kb Al/Cu/CH/Au, 1ps Shot 4, 15th September, 142 J, 1 ps Fully shocked, Delay : 6.5ns Shot 4, 6th September, 140J • Reduction in copper Kalpha counts with shocked targets • He is not observed with both plastic and shocked targets • More careful analysis with a single hit CCD camera is required

23. CRF Foam CPA Au Cu Al Emission is dominated by bremsstrahlung Cold sandwich Al/Cu/Au (5.1um Au) WDM package w/ 3.9um Au WDM package w/ 3.9um Au Cold partially shocked fully shocked 10 ps only (no long pulse) 25um Cu filter 1ps + Long pulse delayed by 5ns Be filter 1ps + Long pulse delayed by 6.5ns Be filter

24. Bremsstrahlung (8keV) / Cu k-a radiograph of long pulse / short pulse driven WDM target 1ps 2ns green Radiograph with long pulse at 5ns (different shot) Short pulse 5ns after long pulse

25. SUMMARY • Experiments have been performed to produce warm dense matter with shock compression. • Rad-hydro simulations show compression of foam to 1 g/cc and temperature of 20-25 eV. The shock timing agrees with experimental results with 200 J, 2 ns, green long pulse laser. • Laser with a pulse length 10 ps burns through 3-4 µm gold foils • Shocked targets show reduction in copper Kalpha counts

26. Future Work • Use of CH as ablator will reduce bremsstrahlung • More shots are required for 1 and 10 ps laser pulse lengths • A detailed data analysis will shed light on the physics of electron transport in warm dense matter