Update on LLNL FI activities on the Titan Laser

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

• Titan operating reliably - _at_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

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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
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The long pulse beam can be moved to any of 6
ports in Horizontal plane
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Titan short pulse has very good pointing and
target alignment accuracy
150µm square foil target
150µm
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Low power images of focal region gives a peak
intensity of 1x1020W/cm2 in 200J, 500fs pulse
300µm
-400µm
-200µm
0µm
400µm
200µm
Best focus
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50
80µm
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On-line fast diode and 2? optical probing are
used to monitor the laser contrast and preformed
plasma
Interferogram at -25ps
Fast diode pre-pulse measurement
Density map
1.38ns
0.18ns
3.18ns
500µm
Diode and preformed plasma measurements can be
obtained to examine shot to shot variations
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Titan data proton beams from gold targets give 2
conversion from laser to protons above 3MeV
Titan Emax vs target thickness
Titan ?lp 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

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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

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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

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Erbium Hydride will be tested on Titan in April 07
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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)
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The long pulse beam will be used to generate FI
scale prepulse inside cones

• 1?,
• E 1 to 100J,
• 3ns,
• Spot 30?m

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Summary

• Titan operating reliably - _at_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