Transcript Document
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 Laser Bay Short-pulse: 300J in 400fs Long-pulse: 1kJ in 3ns Switchyard upgrade will allow simultaneous Titan and Janus 2 beam 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 (5-10m) • Proton beams with slope Tp ~ 4MeV, Emax ~ 40MeV routinely produced with 10m 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 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 The long pulse beam can be moved to any of 6 ports in Horizontal plane Titan short pulse has very good pointing and target alignment accuracy 150µm square foil target 20µm diameter wire target 150µm 500µm Laser and target alignment accuracy and laser pointing stability is 5-10µm Low power images of focal region gives a peak intensity of 1x1020W/cm2 in 200J, 500fs pulse 300µm -400µm -200µm 0µm +200µm +400µm 1.0 Best focus 0.9 0.8 Intensity 0.7 14% 0.6 0.5 0.4 0.3 50% 0.2 0.1 80µm 0.0 -25 -20 -15 -10 -5 0 5 10 Radius (microns) 15 20 25 Best focus 4.9µm FWHM containing 14% of total energy 3x1020W/cm2 15µm diameter spot encircles 50% of total energy 1x1020W/cm2 On-line fast diode and 2 optical probing are used to monitor the laser contrast and preformed plasma Fast diode pre-pulse measurement Density map Interferogram at -25ps -250 3 -200 1.38ns 0.18ns -100 3.18ns 1 Distance (um) 2 500µm Intensity (au) -150 -50 0 50 100 150 0 -5 -4 -3 -2 Time (ns) -1 0 1 200 250 0 25 50 75 100 Distance (um) 2e+19 4e+19 Diode and preformed plasma measurements can be obtained to examine shot to shot variations 6e+19 8e+19 1e+20 Titan data proton beams from gold targets give 2% conversion from laser to protons above 3MeV Laser to Proton conversion % 2.5 Titan data 2 Titan Emax vs target thickness Peak Proton Energy, Ep (MeV) Titan lp vs target thickness 1.5 1 0.5 1/L scaling 40 y = 89.779x-0.4275 R2 = 0.8833 35 Titan data 30 25 Best fit to data 20 15 10 5 0 0 0 20 40 60 80 Target thickness (m) 100 0 100 200 300 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 LSP simulations show very similar behavior to experiments with plausible laser to electron coupling 2-D LSP PIC Simulations Gold substrate 50J, 1MeV electrons Proton Conversion Efficiency (%) 10 Au foil 60 m laser dia 500 fs, 150 J laser 50J, 1 MeV hot electrons t= 700 fs 8 6 LSP 4 2 1/L scaling 0 0 1000 A CHO layer 10 20 30 40 Foil Thickness ( m) • LSP shows slightly higher than 1/L scaling - very similar trend to data • Conversion from hot electrons to protons peaks at 8% for 10m Gold • Implies ~ 30% coupling from laser to 1MeV electron source • Future work will couple PIC code results as input to LSP 50 60 1D simulations predict that High Z hydrides could result in higher conversion efficiency Hot electron to proton conversion eff (%) Hot electron conversion efficiency (%) Hydrides Thot=880keV 5 m Au + 1000ZH B H Z C 40 n 30 Fraction of energy in H+ CH 4 20 CH 2 Fraction of energy in heavy ion CH 10 Current experiments with contaminant layers 0 H LiH CH n MgH CaH 2 ZH 2 CsH ErH 3 UH 3 n • Heavy ions are left behind at back surface during ion separation Erbium Hydride will be tested on Titan in April 07 ErH2 and ErH3 • Films 100nm thick have been manufactured by reactive sputtering* • Oxide and hydrogen barriers may be necessary to maximize hydrogen content * Sandia National lab • Surface contaminants and barrier layers will be removed by ion sputtering** ** M. Allen, P. K. Patel, et al., PRL 93 265004 (2004) 10-15 um gold layer ~1 um Er or U layer 10-30 nm Pd oxidation protective layer Laser 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) The long pulse beam will be used to generate FI scale prepulse inside cones = 1, E = 1 to 100J, = 3ns, Spot ~ 30m 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 (5-10m) • Proton beams with slope Tp ~ 4MeV, Emax ~ 40MeV routinely produced with 10m 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