Liquid DT Layer Approach To Inertial Confinement Fusion

AblatorDT liquid layer(in CH foam)

DT vaporfor 21<T<26 oK
1.0 < ρv < 4.0 mg/cm3

R. E. Olson, R. J. Leeper, S. H. Batha, P.
A . Bradley, B. M. Haines, J. L. Kline, R.
R. Peterson, S. A. Yi, and A. B. Zylstra
Los Alamos National Laboratory
Los Alamos, New Mexico
27th IAEA Fusion Energy Conference
Gandhinagar, Gujarat India
October 22-27, 201812 < CR < 25

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSALA-UR-18-29741

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Liquid DT Layer Approach to ICF Hot Spot Formationsome key points:•DT ice layer implosions have a high hot spot convergence ratio, CR>30.

•Recent cryogenic liquid DT layer implosions at the NIF demonstrate theability to control hot spot CR’s in the range of 12<CR<20.

•

At low CR, DT layered implosion performance is well predicted byradiation-hydrodynamics simulations, but as CR increases, ourunderstanding of hot spot formation decreases.

•There are potential advantages for a liquid DT layered implosion with
reduced hot spot CR (CR<20).

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Potential advantages of a liquid DT layer
key advantages:• A liquid DT layer allows for a higher vapor density compared to a DT ice layer,
the ability to create a hot spot from the vapor, and flexibility in hot spot CR.
• With reduced CR, hot spot formation is expected to be more robust toinstabilities and asymmetries than high CR ice layer implosions.
• With reduced CR, the hot spot pressure required for self-heating is reduced, andthe implosion velocity and fuel adiabat requirements are relaxed. (A trade-off is,that with larger hot spot size, the hot spot energy requirement for self-heating isincreased.)

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advantages of a liquid DT layer:

A liquid DT layer allows for selecting a CR byadjusting the cryogenic fielding temperature.

AblatorAblatorDT ice layer

DT liquid layer(in CH foam)

DT vaporfor 21<T<26 oK1.0 < ρv < 4.0 mg/cm3

DT vaporfor T<19 oK
ρv < 0.4 mg/cm3

CR > 30

12 < CR < 25

*R. E. Olson and R. J. Leeper, “Alternative hot spot formation techniques using liquid DT layer ICF capsules”, Phys. Plasmas 20, 092705 (2013).

Los Alamos National Laboratory

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advantages of a liquid DT layer:

DT layer implosions with reduced CR will have improved robustness toinstability growth and distortions related to engineering features.
Brian Haines RAGE simulations*:
Variations on a full scale HDC
wetted foam capsule design
including detailed and wellresolved models for the capsulefill tube, support tent, surface
roughness, and predicted
asymmetries in the X ray drive.

2D yield / 1D yield

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DT liquid layers(wetted foam)

DT ice layer

hot spot CR*B. Haines et al., “The effects of convergence ratio on the implosion behavior of DT layered ICF capsules,” Phys. Plasmas 24, 072709 (2017).
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NIF sub-scale liquid layer experiments:

Recent experiments on NIF have demonstrated liquid layer
implosions
CH foam-lined
HDC capsule

Au near-vacuum
hohlraum< 900 kJ 3-shock
NIF laser pulse

J. Biener et al., “A new approach to foam-lined indirect-drive NIF ignition targets”, Nuclear Fusion 52, 062001 (2012).
T. Braun et al., “Supercritical drying of wet gel layers generated inside ICF ablator shells”, Fusion Sci. Technol. 73, 229 (2018).
C. Walters et al., “D2 and D-T liquid-layer target shots at the National Ignition Facility”, Fusion Sci. Technol. 73, 305 (2018).

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NIF sub-scale liquid layer experiments:

The NIF cryo team developed thermal designs, along witha process to wick the liquid DT (or D2) into the foam layer.
575 Near-Vacuum Hohlraum
Tcryo = 20-26 oK
ΔT (thermalimpedance)liquid layer capsule
ColdFinger
Frozen plug

Fill tube

Ro = 907 µm
HDC ablator

Very top level procedure:
1. Fill target (liquid wicks into foam)
2. Fix amount of fuel by freezing a plug in the fill tube
3. Hold target and plug temperatures through the shotliquid DT (or D2) layer
Ri = 815 µm

C. Walters et al., “D2 and D-T liquid-layer target shots at the National Ignition Facility”, Fusion Sci. Technol. 73, 305 (2018).

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NIF sub-scale liquid layer experiments:

The initial experiments successfully demonstrated the ability
to select a layered implosion CR in the range of 12<CR<20.
CR = 12
T = 26 oK, ρvapor = 4 mg/cm3(NIF shot N160421)

CR = 17

CR = 20

T = 24 oK, ρvapor = 3 mg/cm3(NIF shot N160626)

T = 21 oK, ρvapor = 1 mg/cm3(NIF shot N161204)

R. E. Olson, R. J. Leeper et al., “First Liquid Layer ICF Implosions at the NIF”,
Phys. Rev. Lett. 117, 245001 (2016).

Los Alamos National Laboratory

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NIF sub-scale liquid layer experiments:

For CR = 12, the hot spot formation is understood– demonstrated
Residuals of Primary Image Reconstruction
by the agreement between experimental data and simulations.
experiment

simulation*DT neutrons (1014)
peak burn time (ns)DT Tion (keV)
DD Tion (keV)burn width (ps)hot spot radius (µm)
X ray image
neutron image

4.5 + 0.1
8.49 + 0.03
3.2 + 0.1
3.0 + 0.2
313 + 30

4.9
8.5
3.3
3.0
275

64.7 + 4.7
50.6 + 2.2

65
47*2D RAGE simulations including drive asymmetry, tent, fill tube,
capsule surface roughness, and low-mode foam shape asymmetries.
*The agreement of the DT ion temperature and the DD ion
temperature is an important feature of this DT liquid layer
experiment. It is usually found in DT ice layer implosions that themeasured DT ion temperature exceeds the expectation fromsimulations⎯an indication of inefficiency in hotspot formation due toincomplete stagnation and residual kinetic energy effects.

experiment
X-ray Emission

N160421 implosion metrics

simulation

Contour Fit of Primary Image Reconstructiona) N160421 Polar GXD

Neutron Emission

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b) N160421
Equatorial GXDc) Synthetic
Equatorial GXDd) N160421
neutron imagee) Synthetic
neutron image

Each image is 200 µm × 200 µm
Composite
Image of Best Pointed Pinholes(Scattered)

R. E. Olson, R. J. Leeper et al., “First Liquid Layer ICF Implosions at the NIF”, Phys. Rev. Lett.
117, 245001 (2016).

Los Alamos National Laboratory

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NIF sub-scale liquid layer experiments:

Although the expected CR control was demonstrated, the observed
over calculated yield decreased dramatically as CR was increased.
2D RAGE simulations including drive asymmetry, tent, fill
tube, capsule surface roughness, and low-mode foam
shape asymmetries.

The data trends might be explained by:•

reduced hydrodynamic coupling efficiency
due to 3D effects1
and/or• anomalously enhanced thermal
conductivity in the DT layer2

1B. M. Haines et al., “3D simulations of NIF wetted foam

experiments to understand the transition from 2D to 3D flow
behavior,” Inertial Fusion Sciences and Application Proceedings(2017)
2A. B. Zylstra et al., “Variable convergence liquid layer implosions

on the National Ignition Facility, Phys. Plasmas 25, 056304 (2018)

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There are tradeoffs involved in high CR ice layer and reduced CR
liquid layer designs• The hot spot pressure required for self-heating is reduced if theCR is reduced (hot spot radius is increased).
• If the hot spot pressure requirement for self-heating is reduced,
the implosion velocity and fuel adiabat requirements arerelaxed.
• With larger hot spot size, the hot spot energy requirement for
self-heating is increased.
• Although there is a penalty to be paid in energy investment for alarger hot spot, it should be noted that there is a significant
benefit in the hot spot alpha particle energy production, which
also increases with the square of the hot spot radius.

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tradeoffs between ice and liquid layer designs:

The hot spot pressure required for self-heating is reduced
if the CR is reduced (hot spot radius is increased).
Prhs α Rhs-1 α CR
Hot Spot Pressure (Gbar)(required for self-heating)

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NIC point design(ice layer, CR ~ 34)
reducedCRHot Spot Radius (µm)
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tradeoffs between ice and liquid layer designs:

If the hot spot pressure requirement for self-heating is reduced,
the implosion velocity and fuel adiabat requirements are relaxed.
Prhs α v5 / β1.5 (isobaric stagnation)

Los Alamos National Laboratory

10/16/18 | 13tradeoffs between ice and liquid layer designs:

With larger hot spot size, the hot spot energy
requirement for self-heating is increased.
Ehs α Rhs2 α CR-2Hot Spot Energy (kJ)(required for self-heating)

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( at fixed ρr )reduced CR(or larger capsules)

Although there is a penalty to be paid in energy investment for a larger hot spot, it should be notedthat there is a significant benefit in the hot spot alpha particle energy production, which also increases
with the square of the hot spot radius.
Los Alamos National Laboratory

10/16/18 | 14tradeoffs between ice and liquid layer designs:

Liquid DT layers offer a modest Convergence Ratio (CR) path to an ICF burning
plasma. However, reduced CR requires more capsule absorbed energy.

Capsule Absorbed
Energy Requirement (kJ)NOTE:This isthe labcolor
palette.

DT liquid layers,
CR ~ 20, Ecap ~ 350 kJ

DT ice layers,
CR ~ 35, Ecap ~ 150 kJ

Hot Spot Convergence Ratio(assumes 1D-like behavior, ρRtot = 2 g/cm2, 10% hydro-coupling)
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Liquid DT layers provide a reduced CR approach to ICF hot spot formation.
However, reduced CR requires more capsule absorbed energy.
Summary and Conclusion• Liquid DT layers provide a reduced CR approach to ICF hot spot formation.
– flexibility in hot spot CR in the range of 12<CR<25– the ability to create a hot spot from the central vapor– improved robustness to instability growth, distortions related to engineering features,and drive asymmetries.
– The hot spot pressure required for self-heating is reduced if the CR is reduced (hotspot radius is increased).
– DT liquid layer implosions and CR control have been demonstrated in sub-scale NIF
experiments.

• Robust reduced CR high adiabat designs require more capsule absorbedenergy.
– > 2x energy investment as compared to a low adiabat CR > 30 DT ice layer design withcomparable ρRtot
Los Alamos National Laboratory> 2x energy investment as compared to a low adiabat CR > 30 DT ice layer design with comparable ρRtot

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back up slides follow

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palette.

Liquid DT Layer Approach to ICF Hot Spot Formation
summary:•DT ice layer implosions have a high hot spot convergence ratio, CR>30.

•Recent cryogenic liquid DT layer implosions at the NIF demonstrate theability to control hot spot CR’s in the range of 12<CR<20.

•

At low CR, DT layered implosion performance is well predicted byradiation-hydrodynamics simulations, but as CR increases, ourunderstanding of hot spot formation decreases.

•There are potential advantages for a liquid DT layered implosion with
reduced hot spot CR (CR<20).

Los Alamos National Laboratory

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NIF sub-scale liquid layer experiments:

As CR increases, our understanding of hot spot formation decreases.

Ion Temperature vs. CR

Burn Width vs. CR

simulation
experiment

hot spot CR

Los Alamos National Laboratory

simulation
experiment

hot spot CR

Hot Spot Pr vs. CR

hot spot Pr (Gbar)

burn width (ps)DT Tion (keV)

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simulation
experiment

hot spot CR

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background and motivation:

The hot spot pressure required for self-heating is reduced
if the hot spot size is increased (Prhs α Rhs-1).
for the hot DT plasma:Phs = 7.52x102 ρ T(Mbar, keV)

multiply and divide by hot spot radius:
Phs = 7.52x102 ρRhs T / Rhs
include the requirement ofρRhs = 0.3 g/cm2 and T > 4.5 keV:Hot Spot Pressure (Gbar)

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NIC point design(ice layer, CR ~ 34)

Phs > 9.0x106 / Rhs (Gbar, cm)
Hot Spot Radius (µm)

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background and motivation:

If the hot spot pressure requirement for self-heating is reduced, theimplosion velocity and fuel adiabat requirements are relaxed (Pr α v5 / β1.5).

assuming isobaric stagnation:
cold fuel kinetic energy, εKE

α vimp2

cold fuel specific energy, εcf

α β ρcf2/3

peak cold fuel density, ρcf

α vimp3 / β3/2

stagnation pressure, Pcfst

α β ρ5/3

hot spot pressure, Phs

Los Alamos National Laboratory

α vimp5 / β3/2

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background and motivation:

With larger hot spot size, the hot spot energy requirement
for self-heating is increased (Ehs α Rhs2 α CR-2).

Hot Spot Energy (kJ)NOTE:This isthe labcolorpalette.

larger capsules

DT liquid layer, OR~1.1 mm, CR=21
DT ice layer design, OR~1.1 mm, CR=34

This analytic hot spot energy scaling (Ehs α Rhs2 α CR-2)
is in agreement with 1D Hydra simulations*.

Hot Spot Radius (µm)

*R. E. Olson and R. J. Leeper, “Alternative hot spot formation techniques using liquid DT layer ICF capsules”, Phys. Plasmas 20, 092705 (2013).

Los Alamos National Laboratory

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NIF sub-scale liquid layer experiments:

For CR = 12, the hot spot formation is well modeled – demonstrated
by the agreement between experimental dataResiduals
and simulations.*of Primary Image Reconstruction
experiment14DT neutrons (10 )Nuclear Bang Time (ns)DT Ti (keV)
DD Ti (keV)
Nuclear Burn Width (ps)Hot-Spot Radius (µm)
X-ray Image
Neutron Image
Inferred Pressure (GBar)
X-ray Image
Neutron Image

Data
4.5 ± 0.1
8.49 ± 0.03
3.2 ± 0.1
3.0 ± 0.2
313 ± 30

2-D HYDRA
6.4
8.6
3.3
3.1
287

1-D RAGE5.7
8.45
3.3
3.0
243

2-D RAGE
4.9
8.5
3.3
3.027564.7 ± 4.7
50.6 ± 2.2

61.8
53

65.4526547

16.5 ± 2.6
23.5 ± 2.6

18.5
23.5

17.3
21.8

17The 2D HYDRA YOC is 70%. The 2D RAGE YOC is 92%, in asimulation including the 30 µm diameter fill tube, the tent,
surface roughness, and low-mode drive asymmetry.

X-ray Emission

Table I: N160421 implosion metrics

simulation

Contour Fit of Primary Image Reconstructiona) N160421 Polar GXD

Neutron Emission

NOTE:
This isthe labcolorpalette.

b) N160421
Equatorial GXDc) Synthetic
Equatorial GXDd) N160421
neutron imagee) Synthetic
neutron image

Each image is 200 µm × 200 µm
Composite
Image of Best Pointed Pinholes(Scattered)*“First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility”, Phys. Rev. Lett. 117, 245001 (2016).

Los Alamos National Laboratory

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