Aug 25, 2008 - 2-D simulations of capsule-cone interaction. â Assessing and controlling cone tip blow-off ... (EOS uncertainty, opacity uncertainties, etc.) ...
Indirect Drive Fast Ignition Target Designs for the National Ignition Facility
Daniel Clark, Richard Town, Max Tabak, and Peter Amendt Lawrence Livermore National Laboratory HEDLP FESAC Subpanel Workshop Washington, D.C. August 25, 2008 Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DEAC52-07NA27344.
NIF will provide a platform for a Fast Ignition (FI) demonstration experiment in the next few years The NIF laser is nearly complete — Indirect drive hot spot ignition campaign will begin in 2010
Advanced Radiography Capability (ARC) Petawatt will be ready by 2011 — 10 kJ in 20 ps and a 140 µm spot — Enable radiography of imploded fuel assembly
A non-cryogenic FI coupling campaign is planned at ignition scale for 2011 - 2012 — ARC upgraded to 9 kJ in 5 ps and 40 µm — Accommodate NIF indirect drive configuration — Develop hydro. equivalent CD targets which meet the requirements for electron coupling demonstration
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Indirect drive Fast Ignition targets have specific hydrodynamic requirements
implode adequate mass to adequate density and ρ r for minimum energy investment
minimize transport distance from cone to fuel
preserve cone and maintain ignitor beam path to fuel assembly
maximize compactness of assembly by minimizing volume of hot spot
minimize blow-off of highZ material from cone tip into ignition region
The NIF FI implosion goal is ρ ~ 300 g/cm3 and ρ r ~ 2 g/cm2 using 0.6 MJ of compression laser energy LLNL-PRES-406504
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Outline Introduction — Indirect drive FI target requirements
Detailed capsule designs — — — —
Single-shock and multi-shock 1-D designs Sensitivity studies to pulse-shaping errors 2-D simulations of capsule-cone interaction Assessing and controlling cone tip blow-off
Hohlraum design — Energetics and symmetry
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A quasi-self-similar, single-shock design was developed to minimize the hot spot in 1-D
1140 1090 1070
Be/Cu (0.9 %) Be
Trad (eV)
1230 µm
DT
870
single-shock pulse shape
200 100
10-6g/cm3 DT
0
10
20
30
time (ns)
m fuel
density (a.u.)
time 1
= 0 . 6 mg
( ρ r ) fuel = 2 . 1 g/cm
2
minimal hot spot volume time 2 time 3
0
1
2
3
radius (a.u.) LLNL-PRES-406504
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The sensitivity of this design to pulse shaping errors is being assessed Applied random drive variations
Distribution of ρr from 400 samples
±100 ps
cumulative probability
nominal
Trad (eV)
probability
distribution
±5% in flux
ρ r (g/cm2)
time (ns)
Further assessments of the design’s robustness to other sources of error (EOS uncertainty, opacity uncertainties, etc.) are planned LLNL-PRES-406504
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Multi-shock NIF-scale designs are also being studied
DT
820
m fuel
100
10-8g/cm3 DT
0
8
16
24
32
time (ns)
= 0 . 8 mg
( ρ r ) fuel = 2 . 2 g/cm
four-shock pulse shape
200
time 1
density (a.u.)
1108
Be
Trad (eV)
1210 µm
2
time 2 time 3
0
1
2
larger hot spot
3
radius (a.u.) LLNL-PRES-406504
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Cone-focused FI implosions are inherently 2-D and involve complex hydrodynamics intersection of orthogonal flows from cone and capsule blow-off
hard x-ray pre-heat induced blow-off of cone within imploding capsule
jetting of assembled fuel into cone and subsequent cone distortion
shear between cone and shell
FI targets afford a large design space of parameters (cone thickness, angle, off-set, etc.) which must be scanned for an optimal design
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In 2-D the single-shock design achieves an acceptably compact fuel mass if there is sufficient cone stand-off 115 µm off-set & 35˚ cone angle
l
tip
itia in
l
ne co
tip
density
itia in
ne co
50 µm off-set & 35˚ cone angle
excessive transport distance between cone and fuel
implosion strongly perturbed from 1-D
Even with a substantial stand-off of the cone tip from the capsule center a damaging axial jet is directed into the cone tip LLNL-PRES-406504
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Narrowing the cone angle diminishes the perturbation to the fuel assembly but causes the cone to collapse 115 µm off-set & 35˚ cone angle tip
p e ti n o c ial init
density
in
l itia
ne co
50 µm off-set & 22.5˚ cone angle
imploding highpressure shell collapses cone
excessive transport distance between cone and fuel
Collapsing of the cone for small angles remains a design challenge — is there an optimal intermediate cone angle? LLNL-PRES-406504
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Cone tip blow-off occurs in this design despite substantial dopant in the ablator Indirect drive designs have high Mand L-band fluxes:
Be ablator
— M-band is absorbed by the ablator — L-band penetrates the ablator and is absorbed by the cone tip — Ablation and recompression of Au is RT unstable and a potential source of high-Z mix in ignition region
DT ice Au cone
initial configuration
recompression
density
peak blow-off
He
material
He Au
Au DT
He Au DT
DT
Tamping of the cone tip with beryllium will be necessary to control the gold blow-off and lining the hohlraum may reduce the L-band source LLNL-PRES-406504
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Hohlraum simulations to assess energetics and symmetry are beginning Simulations so far are run in 2-D without the cone:
6.2 mm
— Peak power: 70 TW
laser power (TW)
— Pulse length: 32 ns
2.5 mm
— Laser energy (3ω): 650 kJ
11.0 mm
— Contrast ratio: 35-to-1
3.0 mm
hohlraum geometry with cone is inherently 3-D
time (ns) LLNL-PRES-406504
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FI demonstration on NIF continues to pose many hydro. design challenges 1-D capsule hydrodynamics
— Continue optimization of designs for maximum ρ r, minimum hot spot size, and minimum total energy — Continue sensitivity studies of designs to pulse shaping uncertainties, EOS uncertainties, etc. — Develop CD non-cryo surrogates and pulse tuning strategy
2-D capsule hydrodynamics — Develop strategy to preserve the cone from jetting or collapse before ignition time — without excessive stand-off or tip thickness — Mitigate cone tip blow-off with increased ablator doping, low-Z tamping of the cone, or hohlraum lining
Hohlraum design — Assess energetics and symmetry of various capsule designs — Assess 3-D impact of cone in hohlraum
FI demonstration on NIF would provide a platform for HEDLP experimental science and a gateway to high gain IFE LLNL-PRES-406504
