1-MJ, Wetted-Foam Target-Design Performance for the ...

1-MJ, Wetted-Foam Targ
for the National

[ nN
*ODMVEJOHJNQS
TVSGBDF
BOE

%
5)[

%HBJOPG







S

T. J. B. Collins
University of Rochester
Laboratory for Laser Energetics

get-Design Performance
Ignition Facility

SJOU
QPXFSCBMBODF

EJDFSPVHIOFTT

44% %FOTJUZ
G HDNm








5JPO LF7



S nN

48th Annual Meeting of the
American Physical Society
Division of Plasma Physics

Philadelphia, PA
30 October–3 November 2006

Summary

A 1-MJ wetted-foam target w
with baseline direct-drive las

• A deuterium–tritium (DT)-saturate
ablator provides better performan
all-DT design.

• Low implosion velocity is used to
imprint.

• A nonuniformity budget analysis
nonuniformity has the greatest ef

• Simulations, including power imb
ice-surface roughness, and imprin
SSD smoothing this target ignites

TC7445

will ignite on the NIF
ser smoothing

ed polymer foam, or “wetted-foam,”
nce than the baseline direct-drive,
o minimize the effects of laser
shows that single-beam
ffect on target performance.
balance, outer-surface and
nt show that with 2-D, 1-THz
s and produces a gain of 32.

Collaborators

R.
T. R.
V. N. G
D. R.
J. P.
J. A. M
R. L. M
P. W. M
P. B.
S. Sk

J. Z

Betti
Boehly
Goncharov
Harding
Knauer
Marozas
McCrory
McKenty
. Radha
kupsky
Zuegel

Outline

• Wetted foams and
• Sources of implos
• Nonuniformity bu
• Integrated simulat
• Experimental plan

TC7446

d the 1-MJ design
sion nonuniformity
udget
tions
ns

At 1.5 MJ, the all-DT design i
to give a 1-D gain of 45

nN$) • Sta
%5 the
she
%5 with
nN WBQPS
En
"MM%5 Tar
〈a〉 = 4.2 Ab
a = P/PFermi A/D
1-D
TC7447
P.
*V. N.

is projected

ability is gauged by the ratio of
e rms bubble amplitude to the
ell thickness A/DR determined
h a 1-D post-processor.*

All-DT

nergy (MJ) 1.5
rget radius (nm) 1695
bsorption (%)
DR (%) 65
D gain 30
45

. W. McKenty et al., Phys. Plasmas 8, 2315 (2001).
Goncharov et al., Phys. Plasmas 10, 1906 (2003).

The 1.5-MJ all-DT design has
resulting in lower gain and s

nN$) nN$) En
%5 %5 Tar
%5 Ab
%5 A/D
nN WBQPS WBQPS 1-D
nN

"MM%5 4DBMFEBMM%5
〈a〉 = 4.2 〈a〉 = 3.5

TC7448

s been scaled to 1 MJ,
stability

All-DT Scaled
All-DT

nergy (MJ) 1.5 1.0

rget radius (nm) 1695 1480

bsorption (%) 65 59

DR (%) 30 33

D gain 45 40

Wetted-foam design

Wetted foam provides higher
allowing a thicker shell and g
than the all-DT baseline targe

nN$) nN$) • The
%5 $) %5
abs
%5
• The
foa

%5 %5 En
nN WBQPS WBQPS Tar
nN Ab

.+ .+ A/D
"MM%5 XFUUFEGPBN 1-D
〈a〉 = 4.2
〈a〉 = 4.9
TC7449
The 1-D, 1-MJ wetted-f

r laser absorption,
greater stability
et at 1 MJ

e foam density balances higher
sorption with increased radiative preheat.
e foam-layer thickness is chosen so the
am is entirely ablated.

All-DT Scaled Wetted-
All-DT foam

nergy (MJ) 1.5 1.0 1.0

rget radius (nm) 1695 1480 1490

bsorption (%) 65 59 86

DR (%) 30 33 11

D gain 45 40 49

foam target gain is 49.

The shell stability can be inc
implosion velocity and raisin

• The most-dangerous Rayleigh
to the inner surface and have
the shell thickness, with wave

• The linear growth of these mo
aspect ratio, IFAR:

Number of e foldings = ct ~ k
• The in-flight aspect ratio depe

velocity and average adiabat:*
IFAR ~

where a = P/PFerm

TC7450

creased by lowering the
ng the in-flight shell thickness

h–Taylor modes feed through
wavelengths comparable to
e numbers k ~ DR–1.

odes depends on the in-flight

kgt2 ~ R0 / IFAR
DR

ends mainly on the implosion
*
V2
a 3/5 ,

mi is the adiabat.

*J. Lindl, Inertial Confinement Fusion (1997).

The foam design has a thicke
velocity than the scaled all-D

V (nm/ns) DR (nm) IF

1-MJ All-DT 430 285 6
Wetted foam 372 323 2

• This improvement comes at
but with improved areal den

• Margin = inward moving kin
peak inward

• The wetted-foam design tole
in 2-D simulations, indicatin

TC7451

er shell and lower implosion
DT design

Areal
FAR A/DR (%) density Margin (%)

tR(g cm–2)

69 33 1.1 45

28 11 1.4 30

t the expense of margin,
nsity.

netic energy at ignition
d kinetic energy

erates realistic ice roughness
ng sufficient margin.

Shell stability and compress
depend on the adiabat

• Minimum energy required for ignitio

• Rayleigh–Taylor instability growth ra

4IPDLCSFBLPVU






"EJBCBU "EJBCBU



*OUP&NJO %FOTJUZ

%5JDF 'PBN


3BEJVT nN


TC7452 *
**

†

sibility

on:*,** Emin ~ a1.88
ate: c = aRT ^kgh1/2 - bRT kVa, Va ~a3/5

*OUP7B
%FOTJUZ HDNm

1PXFS 58




5JNF OT


Adiabat shaping is
achieved using a
decaying-shock picket†

* M. Herrmann et al., Phys. Plasmas 8, 2296 (2001).
* R. Betti et al., Phys. Plasmas 9, 2277 (2000).
† M. Tabak, ICF Program Annual Report, LLNL (1989).

Implosion Nonuniformities

A direct-drive capsule must t
of nonuniformity to ignite an

%SJWF
BTZNNFUSZ

*DFSPVHIOFTT
• Wetted-foam microstructure is a pot

TC6610b

*NQStolerate several sources
nd burn

$BQTVMF
GJOJTI

JOU %5JDF
%5
HBT

tential source of shock nonuniformity.

Nonuniformities: Microstructure

Foam microstructure is pred
minimal effect on target perf

• High-resolution adaptive-mesh-refin
wetted-foam microstructure were us

• After initial undercompression,** the
Rankine–Hugoniot values within a fe



Mix region



Z nN




m
m Y nN


• The fluctuation decay scale length is

This allows simulation of wetted-foam

TC7453 * T. J. B
** G. Ha

dicted to have
formance

nement hydro simulations of the
sed to investigate shock propagation.*

e flow variables asymptote to the
ew percent.

%FOTJUZ HDD

GQH .CBS



s K 2 nm.



%JTUBODFCFIJOETIPDL nN


m layers as a homogeneous mixture.

B. Collins et al., Phys. Plasmas, 12, 062705 (2005).
azak et al., Phys. Plasmas, 5, 4357 (1998).

Nonuniformities: Power Imbalance

Power imbalance has little ef
on target performance

• The NIF beam-to-beam imbalanc
• Beam mistiming of the picket ha

on target performance.*
• The time-dependent illumination

power-imbalance histories** wer
• The average gain reduction due

TC7454 * R. Epstein et
** O. S. Jones e
(SPIE, Belling

ffect

ce perturbation is 8% rms.
as been shown to have little effect
n spectra taken from a series of
re simulated using modes , = 2 to 12.

to these effects was ~6%.

al., BAPS 50, 8114 (2005).
et al., in NIF Laser System Performance Ratings
gham, WA, 1998), Vol. 3492, pp. 49–54.

(BJONonuniformities: Ice Roughness

The wetted-foam design can
initial ice roughness with littl

• The ice-roughness spectrum is giv






*OJUJBMJDFSPVHIOFTT nN


b-layered cryogenic al
at LLE has achieved 1

TC7455

tolerate a 1.75-nm-rms
le reduction in gain

ven by A, = A0 ,–2, primarily in , < 50.

nNSNTJDFSPVHIOFTT
/PPUIFSOPOVOJGPSNJUJFT



%FOTJUZ
HDNm




[ nN









S nN



ll-DT target fabrication
1-nm ice roughness.*

* Craig Sangster, QT1.00001.

Nonuniformities: Surface Roughness

Foam shells have been fabric
with outer-surface rms rough

ON • This spectrum also sho
7BSJBUJPOJOQMBTUJD
'PBNTIFMM

/*'$)TUBOEBSE

m .PEFOVNCFS
m
m A 2-D simulation modeling
modes showed negligible

*Jared Hun
TC7456

cated at General Atomics
hness as low as ~500 nm

PWFSDPBUUIJDLOFTTows an ,–2 dependence.





m

m
i

Surface spectrum from the
atomic-force microscope
Spheremapper at General Atomics*

g this spectrum as ribbon
reduction in performance.

nd, Abbas Nikroo, private communication (2006).

A weighted average v of the
of acceleration is used to pre

• Given the same initial
amplitude, ice modes with
, > 10 are more effective at
reducing the hot-spot size
and quenching burn.*

• A weighted average of the
spectrum has been shown
to map to target gain:**
v2 = 0.06 v,2< 10 + v,2> 9

The target performance is estimated
using the sum in quadrature of v
contributions from each source
of nonuniformity.

TC7457 * R. Kishon
** P. W. McK

ice nonuniformity at the end
edict target performance

(BJO ¤DD
%

5)[44%

¤DD


v nN


ny and D. Shvarts, Phys. Plasmas, 8, 4925 (2001).
Kenty et al., Phys. Plasmas, 8, 2315 (2001).

Nonuniformities: Imprint

The parameter v increases r
as SSD smoothing is decreas

• Multimode simulations incorporating
simulated in 2-D with different levels

• Modes , > 100 do not feed through e
to the ice roughness at the end of th



[ nN


¤DD %FOTJUZ
5)[44% HDNm

vnN






[ nN
¤DD
5)[44%
vnN

TC7458

S nN

rapidly
sed

g imprint modes , = 2 to 100 were
s of SSD.
effectively, contributing negligibly
he acceleration phase.

¤DD v values for
5)[44% imprint alone
vnN
are shown

¤DD
5)[44%
vnN


S nN

2-D SSD appears to be requir

Sources of nonuniformity inc
power imbalance, surface

v (nm) Gain [ nN


2-D 2 × 1 cc 0.94 21 ¤
SSD 1 × 1 cc 1.00 16 %
5)
1-D 2 × 0 cc 2.0 0
SSD I.D. SSD 7.3 0

[ nN



¤
%
5)



TC7459

red for target ignition

cluded 1-nm ice roughness,
e roughness, and imprint



[ nN


DD ¤DD
)[44% %
5)[44%
DD
)[44%

%FOTJUZ
S nN
HDNm




*OEJSFDUESJWF
44%%

DD
()[


S nN

Integrated simulations

A completed 2-D simulation w
produced a gain of 32

• Integrated simulations include imp
nonuniformity (370-nm rms), and 0


[ nN





5



S nN


• Rhot spot = 40 nm, neutron-average

TC7659

with 2-D, 1-THz SSD

print, power imbalance, foam-surface
0.75-nm initial ice roughness.

%FOTJUZ Near peak
HDNm
compression







5JPO LF7




ed fuel areal density = 1.31 g cm–2.

2-D SSD smoothing appears
for the 1-MJ wetted-foam des



[ nN
%FOTJUZ
HDNm


%
5)[44%



S nN


[ nN
%
5)[44%
5JPO LF7
%FOTJUZ

HDNm









S nN


TC7645

to be needed for ignition
sign

%FOTJUZ End of
HDNm
acceleration

%
5)[44%


S nN



% Near peak
5)[44% %FOTJUZ compression

HDNm







S nN

Future Experiments

Foam targets are produced b
and filled and diagnosed at L

• Ice roughness in cryogenic wette
diagnosed with limited sensitivit

• With optical illumination it is diffi
interfaces and layers.

• X-ray phase-contrast imaging is
promising greater sensitivity.





nN










nN

*OOFSTVSGBDFWJTJCMF
VTJOHPQUJDBM*MMVNJOBUJPO

TC7461 *B

by General Atomics
LLE

ed-foam targets is currently
ty using optical shadowgraphy.
ficult to distinguish the various
being implemented at LLE,







1IBTFDPOUSBTUJNBHF
PGBDSZPHFOJD%5GJMMFEGPBNUBSHFU

Bernard Kozioziemski, private communication (2006).

Both planar and spherical we
are being planned at LLE

• VISAR has been used to diagnose
with foams wetted with liquid D2, d
7*4"3


nN %
JO
#SF

5[FSP





• Planar cryogenic experiments will a
and coupling efficiency.

• Progress with b-layering of cryoge
confidence in high-quality wetted-f

TC7462

etted-foam experiments

shock speeds in planar experiments
driven by two 100-ps pulses.
4IPU

%FDBZJOHTIPDL
O%

%JTSVQUJPOCZ
TFDPOEQVMTF
FBLPVUPGGPBN


OT
address shock timing
enic DT targets at LLE gives
foam layering.

A D2-wetted-foam test implos
the highest cryogenic D2 yie

• A high-adiabat pulse was used
• The yield was Y1n = 1.7 × 1011,
• The target was not well charac

to computational uncertainty.
• There remains much scope fo

Unfilled foam Filled cryo
capsule capsu

TC7460

sion produced
eld to date

d.
, 16% greater than the 1-D yield.
cterized, contributing

or experimental exploration.
GMXI

ogenic X-ray image of the
ule imploded core

Summary/Conclusions

A 1-MJ wetted-foam target w
with baseline direct-drive las

• A wetted-foam ablator provides gr
performance than the baseline dir

• Low implosion velocity is used to
imprint.

• A nonuniformity budget analysis s
nonuniformity has the greatest eff

• Simulations, including power imb
ice-surface roughness, and imprin
smoothing this target ignites and

• Future plans include both planar a
wetted foams on OMEGA.

TC7463

will ignite on the NIF
ser smoothing

reater laser coupling and better
rect-drive all-DT design.
o minimize the effects of laser

shows that the single-beam
fect on target performance.
balance, outer-surface and
nt show with 2-D, 1-THz SSD
produces a gain of 32.
and converging experiments with

(BJOThis design is robust due to

• Sensitivity to shock mistiming
the foot-pulse duration.

• This design can tolerate ±200 p
4IPDLUJN







m m

'PPUMFOHUI

TC7464

shock mistiming

is determined in 1-D by varying
ps in shock-timing variation.
NJOHTFOTJUJWJUZ


IWBSJBUJPO OT