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High-Performance Cryogenic Designs for OMEGA and the NIF
V. N. GoncharovUniversity of RochesterLaboratory for Laser Energetics
1
58th Annual Meeting of theAmerican Physical SocietyDivision of Plasma Physics
San Jose, CA31 October–4 November 2016
–25
0
25
–50 0 50Distance (nm)
100
200
300
Dis
tan
ce (n
m)
t (g/cm3)
00
0
10
20
1 2Time (ns)
Ignition hydroequivalentOMEGA design, Rb/Rt = 0.75 (R75)
ASTER simulationOMEGA R75
SDD NIF R75 designEL = 1.6 MJ
Po
wer
(T
W)
DTvapor
450 n
m
8-nm CD
70-nm DT ice
EL = 26 kJ
00
150
3001.2
0.8
0.4
0.04 8 12 16
Time (ns)
Po
wer
(T
W)
tD
r to
tal (
g/c
m2 )
DTvapor
1724
nm
24-nm CD
200-nm DT ice
TC13024
Summary
Reducing cross-beam energy transfer (CBET) losses improves stability properties of ignition spherical direct-drive (SDD) designs at the National Ignition Facility (NIF)
• Hot-spot energy in direct-drive (DD) implosions is a factor of 5 or more larger than that of indirect-drive (ID) implosions
– the required hot-spot pressure in an igniting NIF-scale DD design must exceed 120 Gbar (350 Gbar in ID)
• Without CBET mitigation, SDD designs on the NIF have in-flight aspect ratios in excess of 30
– CBET mitigation in hydroequivalent designs on OMEGA involves reducing beam size relative to the target size* to Rb/Rt = 0.75
– high-yield and ignition SDD designs on the NIF require both beam-size reduction and wavelength detuning**
2
* I. V. Igumenshchev, Phys. Plasmas 17, 122708 (2010); I. V. Igumenshchev, CI3.00002, this conference (invited). ** J. A. Marozas et al., NO5.00009 and P. B. Radha et al., NO5.00005, this conference.
Collaborators
T. J. B. Collins, J. A. Marozas, S. P. Regan, P. B. Radha, E. M. Campbell, D. H. Froula, I. V. Igumenshchev,
R. L. McCrory, J. F. Myatt, T. C. Sangster, and A. ShvydkyUniversity of Rochester
Laboratory for Laser Energetics
3
TC12311e
The hot-spot pressure in an ignition design must exceed a threshold value
4
Direct-drive designs are in a less-challenging hydrodynamic regime with CR K 22 and Phs > 120 Gbar; indirect-drive–ignition targets require CR = 30 to 40 and Phs > 350 Gbar.
~ /P E1th hs
00
100
200
300
400
500
20 40
Pth
(G
bar
)
60Hot-spot energy Ehs (kJ)
80 100
Current high-foot indirect driveRequired: Phs = 350 to 400 GbarAchieved: Phs = 230 Gbar
Energy-scaled current OMEGA (Ehs = 0.44 kJ)Required: 140 GbarAchieved:* 56!7 Gbar
Mitigated CBET
IFAR: in-flight aspect ratio * S. P. Regan et al., Phys. Rev. Lett. 117, 025001 (2016).
• Pressure threshold for ignition
• For direct drive
~ ~ IFARP V P P/ //hs imp a a
1 3 5 30 1 3 a
TC12872a
Coupling losses caused by CBET are larger on the NIF-scale targets because of longer density scale length
5
Laser intensity (#1014 W/cm2)
no CBET
with CBET
NIF
OMEGAA
bla
tio
n p
ress
ure
Pa
(Mb
ar)
250
200
150
100
50
05 6 7 8
Phs ~ PaIFAR5/3
9
Direct-drivedesigns
10
TC13056
CBET losses make ignition target designs too unstable during acceleration
6
20
Yie
ld1-
D (
×10
16)
1
5
10
50
100
500
25 30IFAR
35 40
NIF SDD designsVimp = 3.8 × 107 cm/sFull CBET, Pa = 90 Mbar
Current stability thresholdfor OMEGA cryogenic implosions
1-D LILAC simulations
Gain = 1Ya
Yno a
a = 4.1Phs = 72 GbarCR = 18.5
a = 2.9Phs = 90 GbarCR = 19 a = 1.4
Phs = 130 GbarCR = 21
CR: convergence ratio
Beam 1
Beam 2
CBET
TargetTarget
Beam 1
Beam 2
CBET
R bR b
RtRt
0.10
0.08
0.06
0.04
0.02
0.00700 800 900 1000 1100
Target diameter (nm)
CBETreduction**
Hyd
roef
ficie
ncy
(sh
ell K
E/l
aser
en
ergy
)
Increase in density scale length
TC13057
CBET reduction* and improved laser coupling have been demonstrated on OMEGA by reducing Rbeam/Rtarget
7
** V. N. Goncharov et al., J. Phys. Conf. Ser. 717, 012008 (2016); S. P. Regan et al., presented at the 57th Annual Meeting of the APS Division of Plasma Physics, Savannah, GA, 16–20 November 2015 (CI3.00005) (invited).
KE: kinetic energy * I. V. Igumenshchev, Phys. Plasmas 17, 122708 (2010); D. H. Froula et al., Phys. Rev. Lett. 108, 125003 (2012).
The performance of larger shells is limited by drive asymmetries. The near-term goal is to quantify and reduce laser power imbalance (part of the “100-Gbar” campaign).
Combination of Rb/Rt < 1 and wavelength detuning leads to robust high-yield SDD designs on the NIF
TC13025
8
00
150
3001.2
0.8
0.4
0.04 8 12 16
Time (ns)
201
510
50100
Ya Ya
Rb = Rt
Rb = 0.75 Rt
Yno a
Yno a
500
25 30 35 40
IFAR
R75 with wavelength separation (Dm = !6 Å) Gain = 5; SDD NIF design
Yie
ld1-
D (
×10
16)
Po
wer
(T
W)
tD
r to
tal (
g/c
m2 )
DTvapor
1724
nm
24-nm CD
200-nm DT ice
Initial experiments on the NIF with Dm = !2.3 Å confirmed predicted CBET reduction.*
*J. A. Marozas et al., NO5.00009, this conference.
201
510
50100
Ya Ya
Rb = Rt
Rb = Rt
Rb = 0.75 Rt
Rb = 0.75 Rt
Yno a
Yno a
500
25 30 35 40
IFAR
R75 with wavelength separation (Dm = !6 Å)
Yie
ld1-
D (
×10
16)
20
16
18
20
22
25 30 35 40
IFAR
CR
21
34
5
Ad
iab
at
Combination of Rb/Rt < 1 and wavelength detuning leads to robust high-yield SDD designs on the NIF
TC13058
9
The effect of improved laser coupling on target performance will be tested using an R75 design on OMEGA with improved power balance
TC13059
10
–25
0
25
Dis
tan
ce (n
m)
–25
0
25
–50 0 50Distance (nm)
100
200
300
Dis
tan
ce (n
m)
t (g/cm3)
0
100
200
300
t (g/cm3)
0
00
10
20
1 2Time (ns)
• The effect of CBET is smaller on OMEGA because of shorter scale lengths
• Ignition hydroequivalent OMEGA design Rb/Rt = 0.75, IFAR = 21.8, a = 3Vimp = 3.7 × 107 cm/s
3-D ASTER* simulationsat peak neutron production
Current OMEGAnonuniformitiesPhs = 70 Gbar
“100 Gbar” illuminationuniformity and offsetPhs = 100 GbarP
ow
er (
TW
)
DTvapor
450 n
m
8-nm CD
70-nm DT ice
EL = 26 kJ
*I. V. Igumenshchev et al., Phys. Plasmas 23, 052702 (2016).
TC13024
11
Summary/Conclusions
* I. V. Igumenshchev, Phys. Plasmas 17, 122708 (2010); I. V. Igumenshchev, CI3.00002, this conference (invited). ** J. A. Marozas et al., NO5.00009 and P. B. Radha et al., NO5.00005, this conference.
Reducing cross-beam energy transfer (CBET) losses improves stability properties of ignition spherical direct-drive (SDD) designs at the National Ignition Facility (NIF)
• Hot-spot energy in direct-drive (DD) implosions is a factor of 5 or more larger than that of indirect-drive (ID) implosions
– the required hot-spot pressure in an igniting NIF-scale DD design must exceed 120 Gbar (350 Gbar in ID)
• Without CBET mitigation, SDD designs on the NIF have in-flight aspect ratios in excess of 30
– CBET mitigation in hydroequivalent designs on OMEGA involves reducing beam size relative to the target size* to Rb/Rt = 0.75
– high-yield and ignition SDD designs on the NIF require both beam-size reduction and wavelength detuning**