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Update on LLNL FI activities on the Titan Laser

Update on LLNL FI activities on the Titan Laser. Fusion Science Center Meeting Chicago. A.J.Mackinnon. Feb 28, 2007. Titan laser provides a capability for combined high energy SP and LP beam experiments. Existing Janus Target Area (2x 1kJ LP beams). Titan Target Area.

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Update on LLNL FI activities on the Titan Laser

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  1. Update on LLNL FI activities on the Titan Laser Fusion Science Center Meeting Chicago A.J.Mackinnon Feb 28, 2007

  2. Titan laser provides a capability for combined high energy SP and LP beam experiments Existing Janus Target Area (2x 1kJ LP beams) Titan Target Area Short-pulse: 300J in 400fs Long-pulse: 1kJ in 3ns Laser Bay Switchyard upgrade will allow simultaneous Titan and Janus 2 beam

  3. Outline • Titan operating reliably - @5-7 shots per day • Max irradiance = 3x1020 Wcm-2 at 200J, 500fs. • Prepulse levels low and appear reproducible - working to verify shot to shot diagnostic capability • Pointing accuracy appears to be very good (5-10m) • Proton beams with slope Tp ~ 4MeV, Emax ~ 40MeV routinely produced with 10m gold targets • Fast Ignition relevant experiments to take place in April will study: • laser to hot e coupling • proton conversion from hydride targets • Proton focusing • Aim for 80 shots in 5 week run

  4. Titan long-pulse arm has been operational since Aug 06, enabling 2-beam combined SP-LP experiments Short pulse F/3 focusing optic Long pulse periscope

  5. The long pulse beam can be moved to any of 6 ports in Horizontal plane

  6. 20µm diameter wire target 500µm Laser and target alignment accuracy and laser pointing stability is 5-10µm Titan short pulse has very good pointing and target alignment accuracy 150µm square foil target 150µm

  7. Best focus 4.9µm FWHM containing 14% of total energy  3x1020W/cm2 15µm diameter spot encircles 50% of total energy  1x1020W/cm2 Low power images of focal region gives a peak intensity of 1x1020W/cm2 in 200J, 500fs pulse 300µm -400µm -200µm 0µm +200µm +400µm Best focus 14% 50% 80µm

  8. On-line fast diode and 2 optical probing are used to monitor the laser contrast and preformed plasma Density map Fast diode pre-pulse measurement Interferogram at -25ps 1.38ns 0.18ns 3.18ns 500µm Diode and preformed plasma measurements can be obtained to examine shot to shot variations

  9. Titan data proton beams from gold targets give 2% conversion from laser to protons above 3MeV Titan lp vs target thickness Titan Emax vs target thickness Titan data Titan data Peak Proton Energy, Ep (MeV) Best fit to data Laser to Proton conversion % 1/L scaling Target thickness (m) Target thickness (m) • Conversion efficiency, peak proton energy, proton slope all reduce with increasing target thickness and pulse length • Data being used to benchmark PIC and LSP simulations • Good proton beam obtained at 10ps - encouraging for proton FI

  10. LSP simulations show very similar behavior to experiments with plausible laser to electron coupling Gold substrate 50J, 1MeV electrons 1000 A CHO layer • LSP shows slightly higher than 1/L scaling - very similar trend to data • Conversion from hot electrons to protons peaks at 8% for 10m Gold • Implies ~ 30% coupling from laser to 1MeV electron source • Future work will couple PIC code results as input to LSP

  11. 1D simulations predict that High Z hydrides could result in higher conversion efficiency Fraction of energy in H+ Hot electron to proton conversion eff (%) Fraction of energy in heavy ion Current experiments with contaminant layers • Heavy ions are left behind at back surface during ion separation

  12. ErH2 and ErH3 • Films 100nm thick have been manufactured by reactive sputtering* • Oxide and hydrogen barriers may be necessary to maximize hydrogen content 10-15 umgold layer * Sandia National lab Laser ~1 um Eror U layer • Surface contaminants and barrier layers will be removed by ion sputtering** 10-30 nm Pd oxidationprotective layer ** M. Allen, P. K. Patel, et al., PRL 93 265004 (2004) Erbium Hydride will be tested on Titan in April 07

  13. Main focus of April 07 experiment will be to characterize laser MeV electron coupling Spring expt: Laser to hot E coupling 1. Compare coupling for slabs vs cones 2. Prepulse effect inside cones Long pulse preform beam 3. Pointing and effect of defocus (start)

  14. The long pulse beam will be used to generate FI scale prepulse inside cones • = 1, E = 1 to 100J, • = 3ns, Spot ~ 30m

  15. Summary • Titan operating reliably - @5-7 shots per day (depending on experiment) • Max irradiance = 3x1020 Wcm-2 at 200J, 500fs. • Prepulse levels low and appear reproducible - working to verify shot to shot diagnostic capability • Pointing accuracy appears to be very good (5-10m) • Proton beams with slope Tp ~ 4MeV, Emax ~ 40MeV routinely produced with 10m gold targets • Fast Ignition relevant experiments to take place in April will study: • laser to hot e coupling • proton conversion from hydride targets • Proton focusing • Aim for 80 shots in 5 week run

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