u n c l a s s i f i e d la-ur-06-5159 short-pulse ion acceleration exceeding scaling laws from flat...
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U N C L A S S I F I E D
LA-UR-06-5159
Short-pulse ion acceleration exceeding scaling
laws from flat foils and “Pizza-top Cone” targets at
the Trident laser facility
Kirk FlippoP-24, Los Alamos National Laboratory
November 3rd, 2006 FIW, Cambridge, MA
LA-UR-06-5159
Colleagues and Collaborators
B. M. Hegelich, J. A. Cobble, J. C. Fernández, D. C. Gautier,
R. Johnson, J. Kline, S. Letzring, T. Shimada
P-24, LANL
Jörg SchreiberDepartment für Physik, Ludwig-Maximilians-Universität München
and Max-Planck-Institut für Quantenoptik, München, GERMANY
Marius SchollmeierDarmstadt University of Technology, Institute of Nuclear Physics
GSI, Darmstadt, GERMANY
B. Albright, M. J. Schmitt, L. YinX-1-PTA, LANL
G. Korgan, S. MalekosNanoJems
R. SchulzeMST-6, LANL
S. Gaillard, J. Rassuchine, M. Bakeman, N. Le Galloudec, T.E. Cowan,Nevada Terawatt Facility, University of Nevada, Reno
Ron PereaMST-7
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Outline
• Intro and overview of acceleration mechanisms• TNSA and the Maxwellian spectra• Flat Cu target results• Pizza-top cone target results• Recent Scaling Laws and comparison with current best
scaling laws
LA-UR-06-5159
Proton Acceleration Experiment Setup:Oblique View from 67-degrees to target parallel
67-degrees
Short Pulse
Protons
RCF
Target Rear-side Normal
Target
Top View
Target
RCFIon Beam
ShortPulse To
ThomsonParabolas
Holes for TP Access
RCF Plane
Rear-side Plane
LA-UR-06-5159
Pre-p
ulse Pre-plasma
Pre-p
ulse
Brief Overview of Laser-Ion AccelerationTarget Normal Sheath Accelerations (TNSA)
E
p+e-
rear side p+
e-
targetsp
laser
front side p+Reflected
sp laser
Pre-plasma
target
refluxing e-
Reflected
sp laser
target
e-
e-
1 2
3
Preplasma Formation Hot e- Generation…
e-
… and hot e- RecirculationIon Acceleration
p+ p+
p+
Cold return current e-
p+CH &H2O
E
CH &H2O
E
p+
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Vanadium Ablation Experiment:Actual Laser Heating Shot (no ablation, no Photoshop®)
~1 mm
1 cm
LA-UR-06-5159
Laser accelerated ions typically exhibit a Maxwellian spectrum usually with a cuttoff
LULI, solid target, Hegelich et al., PRL 89 (2002)
RAL, gas targetWei et al., PRL 93 (2004)
LLNL, PW, solid targetSnavely et al., PRL 85 (2000)
LLNL, cluster targetDitmire et al., PRA 57 (1998)
MPQ, Ti:S solid target, Schneider, Hegelich et al., APB 79 (2004)
Jena, water droplet target, Karsch, Hegelich et al., PRL 91 (2003)
CUOS, solid targetMaksimchuk et al. PRL 84 4108 (2000)
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Flat Copper Foil Target RCF up to 23.2 MeV I=1.1x1019 W/cm2,19.6 J, 670fs (expected ~13 MeV)
1.2 MeVBragg Peak = 22.5 MeV 23.2 MeV
HD RCF MD RCF
Beam decreases in size with higher proton energies
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Flat Copper Foil Spectrum I=1.1x1019 W/cm2,19.6 J
0.1
1
10
100
0 5 10 15 20 25
Energy [MeV]
Ap
pro
xim
ate
Pro
ton
Nu
mb
er
[bil
lio
ns/
cm^
2]
.14 J in protons, ~.75% conversion efficiency
LA-UR-06-5159
Typical Pizza-Top Cone Target
Dimensions and material information of a typical target. The target dimensions vary. The Critical Dimension is the inside converging apex and ranges from 4um to 20 um in diameter. The inner target surface may have an adhesive layer less than 200A. The area in between the gold, at the flat foil, may consist of SiO2.
Typical target angle at a cross section of ~50um. However, target angle becomes sharper as you approach the apex
LA-UR-06-5159
Image from the rear side of the RCF stack with LANEX imaging plate showing beam > 35 MeV
Target holder
Cone
target
Proton BeamRCF stack with Lanex on back
Laser
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Pizza-Top Cone Target Beam > 30 MeVI= 11019 W/cm2, 19 J, 605 fs
High energy beam diameter does not change as drastically with energy as in the flat foil case
1.2 MeVBragg Peak = 5 MeV 26.8 MeV
HD RCF CR-39HD RCF
22 - 25.6 MeV
HS RCF Lanex
30+ MeV
LA-UR-06-5159Cut-off extrapolated from flat foils
Pizza-Top Cone Target Spectrum > 30 MeVI= 11019 W/cm2, 19 J, 605 fs
1
10
100
1000
0 5 10 15 20 25 30 35
Energy [MeV]
Pro
ton
Nu
mb
er [
bill
ion
s/cm
^2]
CR-39
Beam seen exiting RCF stack on LANEX was greater than 30 MeV
Scanner RCF imaging spectroscopy gives
~.5 J in protons measured, ~2.5% conversion eff. !
LA-UR-06-5159
Proton energy from cones is dependent on the top to neck ratio
0
5
10
15
20
25
30
35
0 1 2 3 4 5 6 7 8 9 10
Top to Neck Diameter Ratio
Ma
xim
um
Pro
ton
En
erg
y [
MeV
] August Clean March Clean
Flat-tops andfootball-tops
+
+
26.8 MeV Flat Foil Maximum
LA-UR-06-5159
Thinner targets improve the maximum energy of protons and the energy conversion efficiency of cones.
From J. Fuchs et al., Nature Physics 1, 199 (2005)
15 um Cone target
10
15 um Cu target
30
35
15 um Cone target
15 um Cu target
5 um Cu target
35 um Cu target
Trident: =600fs,I=11019 W/cm2
If analysis is done via the method in the paper
LA-UR-06-5159
The proton maximum energy and conversion efficiency correspond to over 3 times the measured intensities.
From J. Fuchs et al., Nature Physics 1, 199 (2005)
30
35
Cone target
Cu target
10
Cu target
Cone target
(laser= 320 fs for protons > 4 MeV)Trident: =600fs,I=11019 W/cm2
LA-UR-06-5159
For the measured pulse duration both the proton maximum and the energy conversion efficiency is enhanced.
From J. Fuchs et al., Nature Physics 1, 199 (2005)
Cu targetCone target
Cu target
Cone target
Trident: =600fs,I=11019 W/cm2
>3.5 times above model in energy
and almost 5 times in Intensity
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Comparison between fluid-model predictions and previously published data of similar conditions
20-μm-thick targets and a 10 μm FWHM laser spot size.
Number of protons in a
1 MeV bin around 10 MeV
From J. Fuchs et al., Nature Physics 1, 199 (2005)
Cu target
Cone targetCu targetCone target
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Conclusions
• Protons from flat foils have been recorded up to 26.8 MeV, which is severaltimes the energy for the thickness, > 3.5 times above scaling for a given pulse duration, and scaling as an experiment with 3 times the intensity on target.
• Protons from cone targets have been observedabove 30 MeV and extrapolated to >35 MeV, and much higher efficiency (~2x) and ~5 times the number than a flat foil!
• Above scaling law energies and efficiencies are due to improved laser condition monitoring, especially pre-pulse levels (contrast).
• Recent RCF calibration using Bragg-peak energies indicates the higher dE/dx for a given particle can lead to a greater OD.
• A different calibration would have a significant impact on the total conversion efficiency numbers due to a difference in total numbers
and Maxwellian temperatures.
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Backup Slides
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Proton Energy Dependence on Pulse Duration for Constant Intensities
y = 0.0106x1.1774
y = 0.3111x0.6455
y = 3E-07x2.7118
y = 0.0807x0.8213
0
5
10
15
20
25
30
500 550 600 650 700 750 800 850
Pulse Duration [fs]
Max
imu
m P
roto
n E
ner
gy
[MeV
]
Cu 1E19 Fe 1.1E19 Cu 8E18 Cu 9.5E18 Power (Cu 1E19)
Power (Fe 1.1E19) Power (Cu 8E18) Power (Cu 9.5E18)
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Flat Foil and Cone Spectra Show Different Temperature Behaviors
Spectra Au Cone and Cu Flat Foil
y = 2E+10e-0.2269x
R2 = 0.9971
y = 3E+09e-0.0955x
R2 = 0.9898
y = 5E+09e-0.2052x
R2 = 0.9953
1.0E+07
1.0E+08
1.0E+09
1.0E+10
1.0E+11
0 5 10 15 20 25 30
Energy [MeV]
Nu
mb
er/M
eV
18582 Au Cone Low Temp Cone High Temp Cone
18497 Cu Foil Low Temp Foil High Temp Foil
Expon. (Low Temp Cone) Expon. (High Temp Cone) Expon. (High Temp Foil)