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Los Alamos National Laboratory

12/6/2016 | 1

UNCLASSIFIED | LA-UR-17-21662

logo/management

Using Double Shell targets for high-yield

experiments at the National Ignition Facility

March 2017, Las Vegas, NV

Target Fabrication Conference

Eric Loomis for Double Shell team



12/6/2016 | 2

UNCLASSIFIED | LA-UR-17-21662 NOTE

standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Double Shells are a large national effort consisting

of theory/modeling, fabrication, and experiment


Doug Wilson

Bill Daughton,

Elizabeth Merritt,

David Montgomery,

Evan Dodd,

Tana Cardenas,

Paul Bradley,

Sasikumar Palaniyappan,

Derek Schmidt,

John Oertel,

Blaine Randolph,

Frank Fierro,

Dru Renner,

John Kline,

Steve Batha

Lawrence Livermore National Laboratory

Peter Amendt,

Bob Tipton,

Vladimir Smalyuk,

Yuan Ping,

Harry Robey,

Jose Milovich,

Jesse Pino,

Morris Wang,

Abbas Nikroo,

Steve Johnson,

Sean Felker,

Chris Choate,

Jeremy Kroll

General Atomics

Haibo Huang,

Hongwei Xu,

Neal Rice,

Martin Hoppe,

Mike Schoff,

Mike Farrell

And many others…


12/6/2016 | 3


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Summary

• Double shell implosions at the National Ignition Facility

use reduced convergence (CR ~ 10) and moderate

implosion velocity (~250 km/s)

• Simulations show that shape and preheat control are

imperative for high yield

• Aluminum outer shell reduces preheat to inner shell

• Controlling high-Z inner shell mix and impact by

engineering features are also vital

• No ablative stabilization and high density mismatch of inner shell

results in small wavelength modes growing rapidly

• Need exquisite surface roughnesses and continued development of

graded density shells


12/6/2016 | 4


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Hohlraum-driven Double Shells offer an

alternate path to 100 kJ yields on NIF

• Potential benefits:• Radiation trapping,

• moderate implosion velocity, and

• moderate convergence ratio

• Double Shells have a unique set of physics uncertainties requiring experimental and computational investigation

high-Z shell

stability

Shell/fuel

mix

Outer shell

in-flight shape

Hard x-ray

pre-heat

Momentum

transfer

Shape

imprinting

Defect/instabili

ty feed-though

Radiation

trapping

• Impact symmetry: Shell uniformity, shell offsets/placement

• High-Z mix: Surface roughness, graded density inner shell development (composition/microstructure

uniformity?)

• Engineering features: Current fill tubes predicted to cause large perturbation. May need to minimize or

reshape joint gaps

Double Shell performance depends on complex target fabrication

DT-filled


12/6/2016 | 5


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Physics of quasi-elastic collisions

applied to double shell design

• Real targets will undergo asymmetric impacts in convergent geometry due

to complex fabrication and non-uniform drive environments

• Modern implosion designs attempt to ‘outrun’ unstable surface roughness

growth (fall-line optimized)


12/6/2016 | 6


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

LANL Double Shell point design

uses 1 MJ into 5.75 mm Au hohlraum

• Al outer shell: Mid-Z to block Au

M-band preheat from reaching

inner shell

• Foam cushion: Minimum density

to maintain high momentum

transfer

• Tamper: low-density, low-Z to

prevent preheat expansion of high-

Z inner shell and to improve

Atwood number

• W inner shell: Heavy metal pusher

on DT to trap radiation in fuel

region and more efficient energy

conversion to fuel

Be – 1.85 g/cc

• 1.8 MJ design also in development

Simulations and experiments are needed to better understand Double

Shell performance sensitivities

NVH 575 Au hohlraum


12/6/2016 | 7


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide. Implosion shape tuned by simple

delay of inner cone pulse

Symmetric implosion requires careful

tuning of laser power and beam pointing

Inner cone delay

Synthetic GXD image

of backlit (Zr, 16.3 keV)

Al outer shell

Inner

cone outer

cone

No inner shell

0.8 ns inner cone delay

• Shape of outer shell imprints onto inner shell at

impact

• Shell non-uniformities or offsets/misalignments will

generate asymmetric shell collision

Beam intensity map


12/6/2016 | 8


Inner shell converging shock results

from shell impact

Equator

Radius (cm)

DTInner

shell

Velocity difference from inner cone delays is

evidence of asymmetric impact of outer shell

Tamper and foamF

luid

velo

city (m

m/n

s)

Solid – 0.8 ns inner cone delay

Dash – 0.6 ns inner cone delay

5.68 ns6.07 ns

Initial configuration

Inner shell

Impact

shock

Asymmetric shell collision


12/6/2016 | 9


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Enormous pressure from impact drives

inner shell implosion

5.9 ns

6.7 ns 7.1 ns

8.7 ns

Hohlraum axis

Radius (cm)

Ra

diu

s (

cm

)

Peak pressure in

foam 1.7 Gbar

• Shape swing in pressure reservoir leads to

asymmetric fuel shape

• Initial shell offsets of 10’s micron will cause

unacceptable implosion asymmetry

Fuel pressure

distribution

Peak pressure in

foam 1.8 Gbar

W

Al

foamBe


12/6/2016 | 10


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Fabrication artifacts can mimic

asymmetries from hohlraum drive

Offset inner shell

Inner shell

Asymmetric impact

Non-uniform shell

Inefficient fuel compression (DT)

shock

shocks


12/6/2016 | 11


Degraded neutron yield results from total

drive and fabrication asymmetries

Yield 3.40e+17

Tion (keV) 12.87

HYDRA shape calculations by D. Wilson and B. Daughton

Location of >2 keV DT Location of dense tungsten

Peak burn time

DT

W

Yield 8.91e+16

Tion (keV) 6.97

Symmetric implosion

With hohlraum asymmetry


12/6/2016 | 12


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Zr backlighter used for imaging

‘surrogate’ inner shells

FY17 and 18 experiments on NIF will test

implosion symmetry and stagnation

DD x-ray self emission will

provide stagnation shapeGlass inner shells provided by GA

Measured impact shape close

to expectations

LANL Al hemi-shell

DT or DD

Inner shell before impact After impact

Joint feature

Stay for Tana Cardenas presentation on fabrication details next…


12/6/2016 | 13


Double shell performance is sensitive to level of

high-Z inner shell preheat

• Aluminum chosen as outer shell material to reduce the amount of preheat reaching inner shell

• Be or Al tamper on inner shell prevents significant preheat expansion of inner shell

Multiplier

Preheat > 3 keV

Neutron

Yield

Inner surface

velocity

(mm/ns)

0 5.39e+17 0.

0.5 4.92e+17 1.19

1 4.90e+17 1.92

2 4.7e+17 2.87

4 2.96e+17 4.18

8 1.82e+16 5.91

Volumetric

heating

Ablation shock

Using Be instead of Al would push closer

to preheat ‘cliff’

Sp

ectra

l brig

htn

ess*k

eV

3

Hohlraum hard x-ray time

dependence

Laser pulse


12/6/2016 | 14


NIF preheat and impact shock experiments will

measure the behavior of outer shell, foam, and

tamper

30 mg/cc CH foam

Al

W on GDP

Main impact shock keyhole

• 1.11 mm outer radius Al shell

• 100 um (or more) Transparent solid (GDP,

SiO2) is placed inside of W shell to slow

down and observe main shock.

• Test effect of with/without Be tamper

Au cone

Liquid D2

Be

W

GDP

Velocity interferometry probe (VISAR)

3-9 keV

preheat shock

VISAR

Main shock


12/6/2016 | 15


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Continued development of tailored inner shells and

reduced surface roughness are crucial for success

• Growth of high-modes on heavy metal inner shell necessitate strict surface roughness limits

• Best performing tamper appears to have minimum density mismatch (Atwood number) to foam and to heavy metal tungsten pusher

HYDRA simulations from B. Daughton (LANL) using NIC

spec surface roughness [Haan et al. Phys. Plasmas (2011)]

Cr tamper

mixes heavily

with foam and

inner shell

Al tamper shows

much lower growth

(Be is similar)

P. Amendt et al, Phys. Plasmas 10 (2003)

Short wavelength

roughness grows fastest


12/6/2016 | 16


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Summary

• Double shell implosions at the National Ignition Facility

use reduced convergence (CR ~ 10) and moderate

implosion velocity (~250 km/s)

• Simulations show that shape and preheat control are

imperative for high yield

• Aluminum outer shell reduces preheat to inner shell

• Controlling high-Z inner shell mix and impact by

engineering features are also vital

• No ablative stabilization and high density mismatch of inner shell

results in small wavelength modes growing rapidly

• Need exquisite surface roughnesses and continued development of

graded density shells


12/6/2016 | 17


simple, text only,

statement layout.

THANK YOU!


12/6/2016 | 18


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Backup slides


12/6/2016 | 19


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

Background physics


12/6/2016 | 20


C-C ( 40 )

D-D ( 40 )

C CD D

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

SIZE DWG NO REV

SHEET OFDRAWN

PI

TITLE

Keyhole Assembly-1

1 1

A3

TFF MST-7 Los Alamos National Labs

Tana Cardenas

PROJECT SHOT DATE

UNLESS OTHERWISE NOTED All Dimensions are Basic

Profile Tolerances

.X = 2

.XX = 0.2

.XXX = 0.02

.XXXX = 0.002

FINISH: 4

(505) 665-0456

APPROVAL

2/1/2017DATE

UNCLASSIFIED WITH UNLIMITED DISTIBUTION

DATE REQUIRED

Notes:

Single Axis Keyhole0.700 mm

0.9

00 m

m

0.260 mm

R0.

418

mm

R0.

438

mm

0.650 mm

1.0

00 m

m

R0.418 mm

R0.458 mm

Plastic Hemisphere

30 um Tungsten

30 um Be

Liduid Deuterium Fill Solid plastic


12/6/2016 | 21


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.


12/6/2016 | 22


standard slide

layout with large,

open, white

space. Try to keep

your slides simple,

and stick to one

thought per slide.

First experiments in FY16 demonstrated

ability to tune outer shell symmetry

N160120-001

1.1 ns cone delay

N160313-002no cone delay

Radiography

axis

0

50

100

150

200

250

300

0 5

Lase

r P

ow

er

(TW

)

Time (ns)

Meas. TotalMeas. OutersMeas. Inners

Time

delay

Shape of Cu-doped Be outer shell

FY17 experiments will begin testing shape

transfer to inner shell

NIF 5.75 hohlraum

Self-emission


12/6/2016 | 23


Graded inner shells materials in

development by GA

W-Si

W-Ti

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