update on llnl fi activities on the titan laser a.j.mackinnon feb 28, 2007 fusion science center...
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Update on LLNL FI activities on the Titan
Laser
A.J.Mackinnon
Feb 28, 2007
Fusion Science Center MeetingChicago
Titan laser provides a capability for combined high energy SP and LP beam experiments
Existing Janus Target Existing Janus Target Area (2x 1kJ LP beams)Area (2x 1kJ LP beams)
Short-pulse: Short-pulse: 300J in 400fs300J in 400fsLong-pulse: Long-pulse: 1kJ in 3ns1kJ in 3nsLaser BayLaser Bay
TitanTitanTarget Target AreaArea
Switchyard upgrade will allow simultaneous Titan and Janus 2 beam
• 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
Outline
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
150µm
Laser and target alignment accuracy and laser pointing stability is 5-10µm
20µm diameter wire target
500µm
Low power images of focal region gives a peak intensity of 1x1020W/cm2 in 200J, 500fs pulse
-400µm -200µm 0µm +400µm+200µm
300µm
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
-25 -20 -15 -10 -5 0 5 10 15 20 25Radius (microns)
Best focus 4.9µm FWHM containing 14% of total energy 3x1020W/cm2
15µm diameter spot encircles 50% of total energy 1x1020W/cm2
Best focus
14%
50%
80µm
On-line fast diode and 2 optical probing are used to monitor the laser contrast and preformed plasma
Diode and preformed plasma measurements can be obtained to examine shot to shot variations
0 25 50 75 100
-250
-200
-150
-100
-50
0
50
100
150
200
250
Distance (um)
Distance (um)
2e+19 4e+19 6e+19 8e+19 1e+20
500µm
Interferogram at -25ps
0
1
2
3
-5 -4 -3 -2 -1 0 1
Time (ns)
Fast diode pre-pulse measurement
0.18ns1.38ns
3.18ns
Density map
Titan data proton beams from gold targets give 2% conversion from laser to protons above 3MeV
• 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
Titan Emax vs target thickness
0
5
10
15
20
25
30
35
40
0 100 200 300
y = 89.779x-0.4275R2 = 0.8833
Target thickness (m)
Peak Proton Energy, Ep
(MeV)
Best fit to data
Titan data
Titan lp vs target thickness
Target thickness (m)
Laser to Proton
conversion %
1/L scaling
Titan data
0
2
4
6
8
10
0 10 20 30 40 50 60
2-D LSP PIC Simulations
Foil Thickness ( )m
1/ L scaling
LSP
Au foil60 m laser dia500 , 150 fs J laser50 , 1 J MeV hot electrons= 700 t fs
LSP simulations show very similar behavior to experiments with plausible laser to electron coupling
• 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
Gold substrate
1000 A CHO layer
50J, 1MeV electrons
1D simulations predict that High Z hydrides could result in higher conversion efficiency
0
10
20
30
40
Hydrides
BC
H LiH CHn
MgH2
CaH2
CsH ErH3
UH3
CH4
CH2
CH
HZ
ZHn
Thot=880keV5 + 1000 m Au Å ZH
n
Fraction of energy in heavy ion
Fraction of energy in H+
• Heavy ions are left behind at back surface during ion separation
Current experiments with contaminant layersH
ot electron to proton conversion
eff (%)
Erbium Hydride will be tested on Titan in April 07
** M. Allen, P. K. Patel, et al., PRL 93 265004 (2004)
• Surface contaminants and barrier layers will be removed by ion sputtering**
• Films 100nm thick have been manufactured by reactive sputtering*
• Oxide and hydrogen barriers may be necessary to maximize hydrogen content
ErH2 and ErH3
10-15 umgold layer
~1 um Eror U layer
10-30 nm Pd oxidationprotective layer
Laser* Sandia National lab
Main focus of April 07 experiment will be to characterize laser MeV electron coupling
2/26/073/5/07
3/12/073/19/073/26/074/2/074/9/07
4/16/074/23/074/30/075/7/07
5/14/075/21/075/28/076/4/07
6/11/076/18/076/25/077/2/077/9/07
7/16/077/23/077/30/078/6/07
8/13/078/20/078/27/07
Switchyard upgrade
High Energy RadiographyLLNLElectron coupling - planar and cones - LLNL/OFES
X-ray scattering - Falcone
TBD - LLNL - expts + maintenance (?)
ILSA - I - Maryland/Colarado (?)
ILSA - II - FSC - Ohio/UCSD -TBD
2. Prepulse effect inside cones
3. Pointing and effect of defocus (start)
1. Compare coupling for slabs vs cones
Spring expt: Laser to hot E coupling
Long pulse preform beam
The long pulse beam will be used to generate FI scale prepulse inside cones
= 1,
E = 1 to 100J,
= 3ns,
Spot ~ 30m
• 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
Summary
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