Saturn Designs for Small Proton-Backlighter Targets at the ...
14
Saturn Designs for Small Proton-Backlighter Targets at the National Ignition Facility R. S. Craxton University of Rochester Laboratory for Laser Energetics 59th Annual Meeting of the American Physical Society Division of Plasma Physics Milwaukee, WI 23–27 October 2017 1 d = 440 nm z 2000 1000 1500 500 0 500 1000 2000 1500 Radius (nm) Laser CH CH n c Y 8 n c Y 8 n c n c z CH CH Laser n c Y 8 n c d = 866 nm
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Transcript of Saturn Designs for Small Proton-Backlighter Targets at the ...
Saturn Designs for Small Proton-Backlighter Targets at the National Ignition Facility
R. S. CraxtonUniversity of RochesterLaboratory for Laser Energetics
59th Annual Meeting of theAmerican Physical SocietyDivision of Plasma Physics
Milwaukee, WI23–27 October 2017
1
d = 440 nm
z2000
1000
1500
500
0
500
1000
2000
1500
Rad
ius
(nm
)
Laser
CHCH
ncY8ncY8
ncnc
z
CHCH
Laser
ncY8
ncd = 866 nm
TC13648
Saturn designs allow more energy to be safely deposited in small proton-backlighter capsules
• Small proton-backlighter capsules are desired for better spatial resolution
• Laser blowby limits the energy that can currently be delivered to small capsules (d K 1 mm)
• A single Saturn ring design allows capsules with diameters from 440 nm to 866 nm to be safely used
2
Summary
Collaborators
E. M. Garcia and L. T. Browning
University of RochesterLaboratory for Laser Energetics
LLE Summer High School Program
S. Le Pape and H.-S. Park
Lawrence Livermore National Laboratory
C. K. Li
Plasma Science Fusion CenterMassachusetts Institute of Technology
A. B. Zylstra
Los Alamos National Laboratory
3
A realistic National Ignition Facility (NIF) laser pulse delivers 50 kJ, of which 21% is absorbed in the capsule
4
Time (ps)
00
20
40
60
80
300 600 900
Po
wer
(T
W)
d = 440 nm3 nm SiO2
Ac (21%)
Incident (2.2 TW/beam, 8 quads, 50 kJ)
Scattered (52%) Atot (48%)
Run G2557TC13649
A few rays pass between the capsule and ring at early times but they are blocked later
5
Run G2557TC13650
z2000
1000
1500
500
0
500
1000
2000
1500
Rad
ius
(nm
)
Laser
t = 100 ps
3%
3% Laser
CHCH
ncY8ncY8
ncnc
3%
3%z
t = 400 ps
360º0º
z
1
4
8
2
16
32
64
kJ/s
r
The scattered-light flux is very small
• Scattered light
6
• Maximum 16 kJ/sr 0.026 J/cm2
at the final mirror
• d = 440 nm
Run G2557TC13651
z
Dev
iati
on
fro
m m
ean
(n
m)
–20
–5
0
–10
5
10
20
180º–180º
The capsule implodes with reasonable uniformity in 3-D
• Center-of-mass radius (400 ps)
7
• vrms = 7 nm (4.8%) mr 148cm n=
• d = 440 nm
Run G2557TC13652
For a given capsule diameter (440 nm), there is a range of acceptable Saturn ring radii
• d = 440-nm capsule
8
Run G2570, G2557, G2579 TC13653
Cen
ter-
of-
mas
s n
on
un
iform
ity
(%)*
Sca
tter
ed li
gh
t (k
J/sr
)
250 350 450 550
Inner ring radius (nm)
650 750
20
15
10
5
0
60
45
30
15
0
Uniformitycompromised
Too muchscattered
light
Design
440 nm 0
* At 400 ps
A Saturn ring with an inner radius of 550 nm is suitable for capsule diameters from 440 nm to 866 nm
9
Run G2557, 6684 TC13654 * At ~2/3 initial radius
Cen
ter-
of-
mas
s n
on
un
iform
ity
(%)*
Sca
tter
ed li
gh
t (k
J/sr
)
200 240 280 320
Capsule radius (nm)
360 400
6
5
4
16
12
8
34
0
440 nm 866 nm0(a, b) = (300, 150) nm
A single elliptical Saturn ring blocks laser blowby for capsule diameters from 440 to 866 nm
10
Runs G2557, 6685TC13655
z2000
1000
1500
500
0
500
1000
2000
1500
Rad
ius
(nm
)
Laser
d = 440 nmt = 400 psAc = 21%
CHCH
ncY8ncY8
ncnc
3%
3%z
d = 866 nmt = 450 psAc = 52%
CHCH
Laser
ncY8
nc
3%
3%
TC13656
Proton probing can be carried out in the horizontal plane if a small portion of the Saturn ring is removed
11
Protons
Protons
Top view
Side view Primary target
For the worst case of 23.5° beams, the peak scattered light varies from 19 kJ/sr for the full ring to 174 kJ/sr for no ring
12
Run 6678, 6680TC13657
z3000
1000
2000
0
1000
3000
2000
Rad
ius
(nm
)
Laserz
Laser
• 19 kJ/sr • 174 kJ/sr
Full-angle opening in ring (°)
00 0.00
0.02
0.04
0.06
0.08
0.10
0.12
20
40
60
80
30 60 90
Pea
k sc
atte
red
-lig
ht
flux
(kJ/
sr)
Flu
x o
n fi
nal
mir
ror
(J/c
m2 )
Safe
Safe based on
Saturn rings with openings up to 46° are safe
13
– x0.35 damage scaling
– shot N150702
Sub1TC13658
x = laser-pulse duration
TC13648a
Saturn designs allow more energy to be safely deposited in small proton-backlighter capsules
• Small proton-backlighter capsules are desired for better spatial resolution
• Laser blowby limits the energy that can currently be delivered to small capsules (d K 1 mm)
• A single Saturn ring design allows capsules with diameters from 440 nm to 866 nm to be safely used
14
Summary/Conclusions
Probing in the horizontal plane is also possible.
