Post on 12-May-2023
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.