1.5
60
50 Gbar 1.0
40
0.5
20
0
700
800
0.0
900 1000 1100
Target diameter (nm)
S. P. Regan
University of Rochester
Laboratory for Laser Energetics
Hydroefficiency
(shell KE/laser energy)
Phs(Gbar)
80
Phs(experiment)/Phs(1-D)
Energy Coupling and Hot-Spot Pressure
in Direct-Drive Layered DT Implosions on OMEGA
0.12
0.10
1-D (beam size = 820 nm)
0.08
0.06
0.04
0.02
0.00
700
800
900 1000 1100
Target diameter (nm)
57th Annual Meeting of the
American Physical Society
Division of Plasma Physics
Savannah, GA
15–20 November 2015
1
Summary
A 50-Gbar hot-spot pressure and an increase in hydroefficiency
have been demonstrated on OMEGA
• A hot-spot pressure of Phs = 56!7 Gbar was inferred from x-ray and
nuclear diagnostics in direct-drive layered DT implosions on OMEGA
• Cross-beam energy transfer* (CBET) was reduced by increasing
the initial target diameter while keeping the laser beam size constant
–– as Rbeam/Rtarget was varied from 1.0 to 0.8, the hydroefficiency
increased by ~40% because of CBET reduction
• Low-mode distortion of the hot spot causes early truncation
of the neutron rate and lower Phs
A path to 100-Gbar hot-spot pressure on OMEGA and spherical-directdrive (SDD) at the National Ignition Facility (NIF) is being developed.
E24558
* I. V. Igumenshchev et al., Phys. Plasmas 17, 122708 (2010);
D. H. Froula et al., Phys. Rev. Lett. 108, 125003 (2012);
V. N. Goncharov et al., Phys. Plasmas 21, 056315 (2014).
2
Collaborators
V. N. Goncharov, T. C. Sangster, R. Betti, T. R. Boehly, M. J. Bonino, E. M. Campbell,
D. Cao, T. J. B. Collins, R. S. Craxton, A. K. Davis, J. A. Delettrez, D. H. Edgell, R. Epstein,
C. J. Forrest, D. H. Froula, V. Yu. Glebov, D. R. Harding, M. Hohenberger, S. X. Hu,
I. V. Igumenshchev, R. T. Janezic, J. H. Kelly, T. J. Kessler, J. P. Knauer, T. Z. Kosc,
J. A. Marozas, F. J. Marshall, R. L. McCrory, P. W. McKenty, D. T. Michel, J. F. Myatt,
P. B. Radha, M. J. Rosenberg, W. Seka, W. T. Shmayda, A. Shvydky, S. Skupsky,
A. A. Solodov, C. Stoeckl, W. Theobald, M. D. Wittman, B. Yaakobi, and J. D. Zuegel
University of Rochester
Laboratory for Laser Energetics
J. A. Frenje, M. Gatu Johnson, R. D. Petrasso
Massachusetts Institute of Technology
S. P. Obenschain, M. Karasik, and A. J. Schmitt
Naval Research Laboratory
D. D. Meyerhofer and M. J. Schmitt
Los Alamos National Laboratory
3
Outline
• 50-Gbar hot-spot pressure
• CBET reduction
• Effect of low-mode distortions on hot-spot pressure
• Path to 100 Gbar on OMEGA and direct drive on the NIF
E24746
4
Outline
• 50-Gbar hot-spot pressure
• CBET reduction
• Effect of low-mode distortions on hot-spot pressure
• Path to 100 Gbar on OMEGA and direct drive on the NIF
E24746a
5
The hot-spot pressure and convergence ratio required for ignition
decreases with increasing energy coupled to the hot spot
Current high-foot indirect drive
Required: Phs = 350 to 400 Gbar
Achieved: Phs = 230 Gbar
|no a ~ 0.7*
500
Pth (Gbar)
400
Energy-scaled current OMEGA (Ein = 0.44 kJ)
Required: 140 Gbar
Achieved: 56!7 Gbar
|no a (energy scaled) ~ 0.7*
300
200
Mitigated CBET
100
0
• Pressure threshold for ignition
0
60
20
40
80
Hot-spot energy Ehs (kJ)
• Generalized Lawson criterion**
| = Px/Px ign = ^tRh0.61 ^0.24 Y 16 /Mh0.34
| OMEGA " | NIF ~ E 0.37
100
Direct-drive ignition: CR† > 22 and Phs > 120 Gbar.
X-ray-drive ignition: CR = 30 to 40 and Phs > 350 Gbar.
TC12311g
Pth + 1/ E hs
* R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015);
A. R. Christopherson, CI3.00006, this conference (invited).
** R. Betti et al., Phys. Plasmas 17, 058102 (2010).
†
CR: convergence ratio
6
Layered DT targets were imploded on OMEGA for the 50-Gbar campaign*
Laser drive
Target
Single picket
Triple picket
30
Target-design parameters
Vimp = 3.6 to 3.8 × 107 cm/s
a = 2.5 to 4.5
CR = 20 to 23
IFAR** = 15 to 25
8 nm CD
DT gas
10
26 kJ
0
nm
20
430
Power (TW)
50 nm DT
a = P/PF
IFAR = shell radius/
shell thickness
Sources of low-mode drive nonuniformity
0
1
2
Time (ns)
3
1.Laser beam power imbalance (15% to 20%)
2.Target offset (5 to 30 nm)
3.Laser beam mispointing (10-nm rms)
OMEGA layered DT implosions are hydrodynamically
scaled from the NIF direct-drive–ignition design.
TC12314c
* V. N. Goncharov et al., UO4.00005, this conference.
** IFAR: in-flight aspect ratio
7
Improvements to the laser, target, and diagnostics
were required to increase Phs on OMEGA
• Laser
–– SG5 phase plates (820 nm diameter, 95% energy encircled)
–– multipulse driver [more energy on target, apply smoothing
by spectral dispersion (SSD) to pickets only]
• Target—Isotope Separator System
–– D:T is 50:50 at the inner ice layer and gas vapor with <0.1% H
• Diagnostics
–– high-temporal (30-ps) and spatial-resolution (6-nm)
Kirkpatrick–Baez microscope (KBframed)
–– neutron temporal diagnostic with 40-ps temporal
response (P11NTD)
E24748
8
A new set of phase plates designed to improve the on-target
drive uniformity were developed for this campaign
I + exp 9_- r r0inC
y far field (nm)
Log scale of far field from
previous SG4 equivalent-targetplane (ETP) image
800
Log scale of far field from
new SG5 equivalent-targetlog10 (I)
plane (ETP) image
0
–1
400
0
860 nm, 95%
820 nm, 95%
–2
–400
–3
–800
–4
–500
0
500
x far field (nm)
–500
0
500
x far field (nm)
E23691d
9
The 16-channel, gated, Kirkpatrick–Baez microscope (KBframed)
measures the evolution of the hot-spot size around stagnation
OMEGA cryogenic DT target implosion, shot 76828
PSF*
t = 2.717 ns
t = 2.729 ns
t = 2.766 ns
t = 2.774 ns
t = 2.786 ns
t = 2.792 ns
t = 2.811 ns
t = 2.825 ns
t = 2.838 ns
t = 2.855 ns
100 × 100-nm regions
0
Max
Relative x-ray intensity
KBframed has 30-ps temporal resolution and 6-nm spatial resolution,
and records an image every 15 ps in the 4- to 8-keV photon-energy range.
E24014c
F. J. Marshall et al., UO4.00004, this conference; F. J. Marshall, Rev. Sci. Instrum. 83, 10E518 (2012).
* PSF: point spread function
10
The neutron rate is recorded with the neutron temporal diagnostic (NTD*)
Neutron rate (1/s)
1024
Shot 76607, NTD
Simulation convolved
with IRF**
1023
Measurement
Time
error
1022
1021
2.5
2.6
2.7
2.8
2.9
3.0
Time (ns)
P11NTD can measure a minimum burnwidth of 50 ps with a 10% accuracy
and absolute bang time !25 ps (signal-to-background is ~100).
TC12365c
* C. Stoeckl et al., “A Neutron Temporal Diagnostic for High-Yield DT Cryogenic
Implosions on OMEGA,” to be submitted to the Review of Scientific Instruments.
** IRF: instrument response function
11
A primary DT neutron yield up to ~5 × 1013
with a tR of ~200 mg/cm2 has been recorded
Measured Y/1-D Y
Measured Y (×1013)
6
5
4
3
2
100
200
Measured tR (mg/cm2)
300
1.0
0.8
0.6
0.4
0.2
0.0
0
0.2 0.4 0.6 0.8 1.0
Measured tR/1-D tR
Yield-over-clean (YOC) / measured Y/1-D Y = 0.2 to 0.6
tROC / measured tR/1-D tR = 0.5 to 1
Ti = 2.7 to 3.8 keV
E24749
12
A hot-spot pressure of 56!7 Gbar was inferred from nuclear
and x-ray diagnostics assuming isobaric hot spot*
N max = n T n D T 2
#Vhs dV vv
T2
N max = 2Y ln 2 r Dt burn
(assuming a Gaussian neutron rate with FWHM** = Dtburn)
Phs - ;8Y ln 2 r bDt burn
#Vhs dV vv
T2
1/2
lE
OMEGA cryogenic target shot 77066
R17 = 22.0!0.4 nm (KBframed + framed pinholes)
Y = 4.0 × 1013
Dtburn = 63!5 ps (x rays), 67!5 ps (neutrons), 66 ps (1-D)
GTiHn = 3.2!0.4 keV
Phs, exp = 56!7 Gbar
Phs, 1-D = 90 Gbar
a = 3.3
E23702c
T ^r h = Tc 91 – _r R hsi ^1 –
2
2/3
3
/
2
0.15 hC
Tc is the maximum hot-spot temperature
Ti
n
=c#
V hs
dV v v
R hs = 1.06 R 17
T
#Vhs dV vv
T 2m
* C. Cerjan, P. T. Springer, and S. M. Sepke, Phys. Plasmas 20, 056319 (2013);
R. Betti et al., Phys. Plasmas 17, 058102 (2010).
** FWHM: full width at half maximum
13
Outline
• 50-Gbar hot-spot pressure
• CBET reduction
• Effect of low-mode distortions on hot-spot pressure
• Path to 100 Gbar on OMEGA and direct drive on the NIF
E24746b
14
Rb/Rt was varied from 1.0 to 0.8 by changing
the target diameter to reduce CBET*
Beam 2
CBET
Target
Beam 1
Beam 2
CBET
Ablation pressure (Mbar)
350
300
250
1.0, no CBET
200
150
1.0, CBET
100
Rb /Rt = 0.5
Rb /Rt = 0.7
Rb /Rt = 0.8
50
0
1.0
Rt
2.0
2.5
3.0
3.5
Shell convergence ratio during laser drive
The target diameter is varied from 800 to 1000 nm, while
keeping the laser beam size constant, to reduce CBET.
Rb
Beam 1
TC12317b
1.5
* I. V. Igumenshchev et al., Phys. Plasmas 17, 122708 (2010); D. H. Froula et al., Phys. Rev. Lett. 108, 125003 (2012);
V. N. Goncharov et al., Phys. Plasmas 21, 056315 (2014); V. N. Goncharov et al., UO4.00005, this conference.
15
CBET modeling is required in the 1-D simulation to match the measurements*
OD = 1017 nm
I = 0.7 × 1015 W/cm2
fabs, expt = 75 !2%
fabs, 1-D with CBET = 77%
fabs, 1-D without CBET = 92%
• Absorption reduced 16% by CBET
Power (TW)
• Absorption reduced 27% by CBET
30
Shot 77335 (H13B)
Laser
Scattered light
1-D with CBET
1-D without CBET
Measured
20
10
0
30
Power (TW)
Outside diameter (OD) = 805 nm
I = 1.1 × 1015 W/cm2
fabs, expt = 54 !6%
fabs, 1-D with CBET = 52%
fabs, 1-D without CBET = 71%
Shot 76360 (H13B)
1-D simulation includes*
20
• nonlocal thermal
conduction
10
0
• first-principles
equation of state**
0
1
2
Time (ns)
The effect of CBET is reduced for the larger target.
E24763
* V. N. Goncharov et al., Phys. Plasmas 21, 056315 (2014).
** S. X. Hu et al., Phys. Rev. E 92, 043104 (2015).
16
CBET modeling is required in the 1-D simulation to match the measurements*
Shot 76607, self-emission imaging**
Ablation front
CD/DT interface
500
20
300
15
200
10
100
5
0
0
0
1
2
Power (TW)
25
400
Distance (nm)
30
Time (ns)
The measured shell trajectory constrains the model during the acceleration phase.
TC12365e
* V. N. Goncharov et al., Phys. Plasmas 21, 056315 (2014).
** D. T. Michel et al., Phys. Rev. Lett. 114, 155002 (2015).
17
CBET modeling is required in the 1-D simulation to match the measurements*
Neutron rate (1/s)
1024
Shot 76607, NTD
Simulation convolved
with IRF
1023
Measurement
Time
error
1022
1021
2.5
2.6
2.7
2.8
2.9
3.0
Time (ns)
The measured neutron rate shows deviation from the 1-D prediction near stagnation.
TC12365d
* V. N. Goncharov et al., Phys. Plasmas 21, 056315 (2014).
18
More kinetic energy is coupled to the larger target
because of a reduction in CBET
Vimp, 1-D = 3.6 × 107 cm/s for both designs
Ablation front
CD/DT interface
Ablator
400
300
200
100
0
0
1
2
Time (ns)
3
600
500
400
300
200
100
0
nm
25
50 0
nm
450
Distance (nm)
Position (nm)
Shot 76607
DT ice
EKE shell (1-D) = 1.9 kJ
Shot 76362
20
15
10
5
0
1
2
3
Power (TW)
DT ice
EKE shell (1-D) = 1.3 kJ
500
Ablator
0
Time (ns)
1-D simulations agree with the measured shell trajectories; energy
coupling to the imploding shell is taken from the 1-D simulation.
E24015d
19
An ~40% increase in the hydrodynamic efficiency
was inferred because of a reduction in CBET
Hydroefficiency
(shell KE*/laser energy)
0.12
0.10
1-D (beam size = 820 nm)
1-D (beam size = target size)
0.08
Increase caused
by CBET reduction
0.06
0.04
Increase
in density
scale length
0.02
0.00
700
800
900
1000
1100
Target diameter (nm)
Measured shell trajectories for 860-nm, 900-nm, and 1000-nm
targets with a fixed beam size constrain the 1-D simulations.
E24751
* KE: kinetic energy
20
The observed increase in energy coupling with target diameter
does not result in a higher hot-spot pressure
1.5
Phs(Gbar)
60
50 Gbar 1.0
40
0.5
20
0
700
800
900
1000
Phs(experiment)/Phs(1-D)
80
0.0
1100
Target diameter (nm)
The peak hot-spot pressure of 56!7 Gbar inferred for the smaller
targets corresponds to 50% to 65% of the 1-D prediction.
E24751a
21
Outline
• 50-Gbar hot-spot pressure
• CBET reduction
• Effect of low-mode distortions on hot-spot pressure
• Path to 100 Gbar on OMEGA and direct drive on the NIF
E24746c
22
Three-dimensional simulations predict early burn truncation
because of low-mode (, # 5) hot-spot distortion growth
3-D ASTER* simulations
for a 860-nm OD target
Perturbation sources
2
Neutron rate (1/s)
1
TC12376b
1025
1-D
3-D
1022
1021
2.4
• 20-nm target offset
• 10-nm rms laser beam mispointing
Larger targets have a higher level
of low-mode drive nonuniformity
because of reduced beam overlap.
2
1
2.5
• 15% rms laser power imbalance
1-D: symmetric
3-D: perturbed
1024
1023
80 nm
Density
2.6
Time (ns)
2.7
* I. V. Igumenshchev et al., UO4.00015, this conference.
23
The measured neutron rate shows burn truncation similar to the 3-D simulation
Experiment
1-D simulation convolved with IRF
Neutron rate (1/s)
1025
Shot 77335
a = 3.7
OD = 804 nm
1024
1023
0.36 × 1-D n
1-D like
1022
1021
–0.2
–0.1
0.0
0.1
0.2
t – tbang time (ns)
E24752a
The measured rising slope deviates from the 1-D prediction around
1023 s–1 and the peak measured neutron rate is 36% of the 1-D value.
n: neutron rate
24
The measured neutron rate shows the onset of burn truncation
occurs earlier for the larger targets
Experiment
1-D simulation convolved with IRF
Neutron rate (1/s)
1025
1024
1023
0.15 × 1-D n
0.36 × 1-D n
1-D like
1-D like
1022
1021
–0.2
˚
–0.1
0.0
0.1
t – tbang time (ns)
E24752
Shot 76360
a = 3.8
OD = 1017 nm
Shot 77335
a = 3.7
OD = 804 nm
0.2
–0.2
–0.1
0.0
0.1
0.2
t – tbang time (ns)
The measured rising slope deviates from the 1-D prediction around
1022 s–1 and the peak measured neutron rate is 15% of the 1-D value.
25
The 1-D predictions are closer to the inferred Phs and tR in implosions
with CR < 17 and a > 3.5 when burn truncation is included in the analysis
1-D tR averaged over experimental burn
(with burn truncation)
1-D pressure at experimental peak burn
1.1
GtRHn, exp GtRHn,1-D
1.1
Pn, exp Pn, 1-D
1.0
0.9
0.8
0.7
0.6
0.5
0.4
14
15
16
17
18
19
1-D convergence ratio
(experimental bang time)
20
1.0
0.9
Target OD
1000nm
nm
960
nm
960 nm
900
nm
900 nm
860
nm
860 nm
800
800 nm
0.8
0.7
0.6
0.5
0.4
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Adiabat
Low-mode distortion of the hot-spot is the primary factor degrading
target performance for the high-adiabat OMEGA DT cryo implosions.
TC12326b
26
Outline
• 50-Gbar hot-spot pressure
• CBET reduction
• Effect of low-mode distortions on hot-spot pressure
• Path to 100 Gbar on OMEGA and direct drive on the NIF
E24746d
27
The National Direct-Drive Program has four elements
1.Hydro-equivalent implosions on OMEGA
–– demonstration and physics understanding of ignitionrelevant hot-spot pressure (100 Gbar)
–– OMEGA experiments will also demonstrate laser–plasma interaction (LPI)
control (CBET mitigation: laser-beam zooming, wavelength detuning,
preheat mitigation) strategies
2.LPI, energy coupling, imprint mitigation at MJ-scale plasmas on the NIF
–– will involve both planar and implosion platforms
3.Strategy for conversion of the NIF to SDD
–– cost, schedule, phased approach
–– laser technology development
4.Robust target designs for a range of performances
The National Direct-Drive strategy involves multiple laboratories.
E24753
28
Summary/Conclusions
A 50-Gbar hot-spot pressure and an increase in hydroefficiency
have been demonstrated on OMEGA
• A hot-spot pressure of Phs = 56!7 Gbar was inferred from x-ray and
nuclear diagnostics in direct-drive layered DT implosions on OMEGA
• Cross-beam energy transfer* (CBET) was reduced by increasing
the initial target diameter while keeping the laser beam size constant
–– as Rbeam/Rtarget was varied from 1.0 to 0.8, the hydroefficiency
increased by ~40% because of CBET reduction
• Low-mode distortion of the hot spot causes early truncation
of the neutron rate and lower Phs
A path to 100-Gbar hot-spot pressure on OMEGA and spherical-directdrive (SDD) at the National Ignition Facility (NIF) is being developed.
E24558
* I. V. Igumenshchev et al., Phys. Plasmas 17, 122708 (2010);
D. H. Froula et al., Phys. Rev. Lett. 108, 125003 (2012);
V. N. Goncharov et al., Phys. Plasmas 21, 056315 (2014).
29