Diagnosing Implosion Performance at the NIF by Means of

Neutron-Spectrometry and Neutron-Imaging Techniques

Presentation to

24th IAEA Fusion Energy Conference

San Diego, CA, USA

October 8-13, 2012

Johan Frenje on behalf of the NIF team

Massachusetts Institute of Technology

Collaborators

UR

J. Knauer

V. Glebov

T. Sangster

C. Abbott

R. Betti

M. Burke

T. Clark

N. Fillion

V. Glebov

T. Lewis

O. Lopez-Raffo

J. Magoon

P. McKenty

D. Meyerhofer

B. Rice

P. Radha

M. Romanovsky

J. Szcepanski

M. Shoup

R. Till

MIT

D. Casey

M. Gatu Johnson

C. Li

M. Manuel

H. Rinderknecht

M. Rosenberg

F. Séguin

N. Sinenian

A. Zylstra

R. Petrasso

GA

J. Kilkenny

A. Nikroo

L. Reny

M. Farrel

D. Jasion

SNL

R. Leeper

LANL

G. Grim

N. Guler

J. Kline

G. Morgan

T. Murphy

D. Wilson

LLNL

R. Ashabranner

R. Bionta

E. Bond

J. Caggiano

M. Eckart

D. Fittinghoff

E. Hartouni

J. McNaney

M. Moran

D. Munro

S. Sepke

P. Springer

D. Bleuel

A. Carpenter

C. Cerjan

J. Edwards

B. Felker

S. Glenzer

Imperial College

J. Chittenden

B. Appelbe

S. Hatchett

R. Hollaway

O. Jones

R. Kauffmann

D. Koen

O. Landen

J. Lindl

D. Larson

S. Le Pape

M. Mckernan

A. Mackinnon

E. Moses

H. Park

P. Patel

R. Prasad

B. Remmington

R. Rygg

V. Smalyuk

P. Springer

R. Zacharias

M. Yeoman

2 Johan Frenje – IAEA 2012

This work performed under the auspices of the U.S. Department of Energy by

Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Summary

The neutron data have been essential to the

progress of the experiments on the NIF

• The neutron-spectrometry data indicate that the tuning campaigns have improved

the implosion performance by ~50× since the 1st shot in Sept 2010.

• We have achieved a radial convergence of ~35, fuel ρR values up to ~1.3 g/cm2,

and inferred hot-spot pressures up to ~150 Gbar.

• The maximum pressure is ~2× lower than point design, and the observed neutron

yields are 3-10× lower than expected.

• The pressure and yield deficits are most likely explained by higher than predicted

fuel-ablator mix and ρR asymmetries often observed in the implosions.

• A path forward to address these issues has been defined.

3

4

Primary neutrons (n):

• Yn

• Ti

• Residual kinetic effects

Scattered neutrons (n’):

• rR

rR (g/cm2) 21dsr10-12 MeV1)

dsrY

YR

n

n 'r

2Di ET

Johan Frenje – IAEA 2012

The neutron spectrum is used to diagnose neutron yield (Yn),

ion temperature (Ti) and areal density (ρR)

1014

1015

1016

1017

1018

1019

0 5 10 15 20

Yie

ld /

MeV

MeV

DEIgnition

Measurement of the detailed shape of the low-energy part of

neutron spectrum provides 3D information about implosion

1) J.A. Frenje et al., these proceedings; to be submitted to Nucl. Fusion.

Neutron spectrum

n

n’

Primary and scattered neutrons are imaged to diagnose neutron-

source size (R) and thickness of high-density shell (R), resp.

Neutron images

5 Johan Frenje – IAEA 2012

Primary neutrons (n):

• R of neutron source

Scattered neutrons (n’):

• R of high-density shell

Hot DT core High-density

Shell (R)

Neutron

source (R)

n'

n'

n

High-density

shell

Neutron

source

50

-50

0 μm

Images of neutron source

and high-density shell

G. Grim et al., APS invited (2012).

Several neutron spectrometers and an imaging system

have been fielded at various locations on the NIF

MRS (77-324)

NITOF/NIS (90-315)

Spec-E (90-174)

Spec-A (116-316)

nTOF4.5m (64-330) nTOF3.9m (64-275)

M. Gatu Johnson et al., RSI (2012).

F.E Merrill et al., RSI (2012). 6 Johan Frenje – IAEA 2012

Neutron spectrometry and neutron imaging

This provides good implosion coverage for reliable

measurements of Yn, Ti, rR, and rR asymmetries

1012

1013

1014

1015

5 10 15Neutron energy [MeV]

Yie

ld / 1

00 k

eV

102

103

104

0 5 10 15

Co

unts

/ M

eV

Deuteron energy [MeV]

Single-scattering

Primary peak

(unscattered)

Neutron spectrum

Single-scattering

Primary peak

MRS spectrum1)

Rn = 28 ± 3 μm n

n’ Rn’ = 44 ± 5 μm

Shot N120205

Yn = (5.6 ± 0.2)×1014

ρR = 900 ± 40 mg/cm2

Ti = (3.4 ± 0.1) keV

Johan Frenje – IAEA 2012

Spectra and images are now measured routinely

on the NIF (Example: DT shot N120205)

Data

7

1) J.A. Frenje et al., PoP (2010). 2) G. Grim APS invited, PoP (2012).

Neutron images2)

1013

1014

1015

1016

0 0.50 1.0 1.5

Yn

rR [g/cm2]

Data

The spectrometry data indicate that the tuning campaigns

have improved the implosion performance by ~50× since Sept 2010

32

4711523

.n

.

R

e.

YITFx

r

Lawson-type parameter2):

ITFxE

E

losses

1) M .J. Edwards et al., PoP (2011); A.J. Mackinnon et al., PRL (2012). 2) R. Betti et al., OV/5-3

8

Implosion performance1):

Sep 2010

Mar 2012

0.1

0.01

0.05

0.02

0.002

ITFx

1.0

0.5

0.2

0.005

Ignition

conditions Hot-spot energy: 3 kJ

Alpha heating: 0.5 kJ

Neutron heating: 0.3 kJ

Johan Frenje – IAEA 2012

Untuned 09/10 – 02/11 Symmetry 11/11 – 12/11

Shock timing 06/11 Mix/No Coast 03/12 – 07/12

Velocity 08/11 – 09/11

0

0.5

1.0

1.5

0 500 1000 1500 2000 2500

rR

[g

/cm

2]

R2 [m

2]

Spectrometry and imaging data self-consistently indicate that

the tuning campaigns have improved the convergence by ~2×

Data

9

Untuned 09/10 – 02/11

Shock timing 06/11

Velocity 08/11 – 09/11

Symmetry 11/11 – 12/11

Mix/No Coast 03/12 – 07/12

Sep 2010

Mar 2012

2

24

R

R

mR fuel

r

Sept 2010 R2 data inferred from x-ray images.

(fit to all neutron-imaging data)

16.049.0

R

R

High-density fuel shell

Source

R ΔR

Johan Frenje – IAEA 2012

1012

1013

1014

1015

1016

1017

N1

10121

N1

10212

N1

10608

N1

10620

N1

10826

N1

10908

N1

11029

N1

11112

N1

20114

N1

20131

N1

20213

N1

20311

N1

20321

N1

20405

N1

20417

N1

20626

N1

20720

N1

20808

Yn

0

100

200

300

0.0 0.50 1.0 1.5 2.0

Ho

t-s

po

t p

ress

ure

[G

bar]

rR [g/cm2]

Inferred hot-spot pressure is ~2× lower than point design,

and yields are ~3-10× lower than predicted

Data

What’s causing this pressure and yield deficit?

Point design: ~300 Gbar

Untuned 09/10 – 02/11 Symmetry 11/11 – 12/11

Shock timing 06/11 Mix/No Coast 03/12 – 07/12

Velocity 08/11 – 09/11 LASNEX 2D sim.

HYDRA 3D sim.

DATA

Mar 2012

Sep 2010

10 Johan Frenje – IAEA 2012

1) P. Springer et al., IFSA (2011).

1014

1015

1 2 3 4 5

Yn

Ti [keV]

The pressure and Yn deficits can be explained partly by

larger than predicted CH-ablator mixed into the hot spot

11

Untuned 09/10 – 02/11

Shock timing 06/11

Velocity 08/11 – 09/11

Symmetry 11/11 – 12/11

Mix/No Coast 03/12 – 07/12

7.4

in TY

Fuel-ablator mix

very significant

The higher-convergence implosions display more mix, which reduces

Ti and Yn. Other data indicate that the “mix-performance cliff” occurs

at a remaining shell mass that is ~30-40% larger than the point design

Johan Frenje – IAEA 2012

Data

0

0.5

1.0

1.5

2.0

0 0.5 1.0 1.5 2.0

MRS rR [g/cm2]

Sp

ec

-E r

R [

g/c

m2]

0

0.5

1.0

1.5

2.0

0 0.5 1.0 1.5 2.0

Sp

ec

-E r

R [

g/c

m2]

Spec-A rR [g/cm2]

The Yn and pressure deficits can also be explained partly by

the systematic low-mode ρR asymmetries often observed

12

MRS

Spec-E

Spec-A

10-12 MeV 10-12 MeV

Neutron measurements of un-

scattered neutrons also indicate

similar low-mode ρR asymmetries

Johan Frenje – IAEA 2012

Data

0

0.5

1.0

1.5

2.0

0 0.5 1.0 1.5 2.0

MRS rR [g/cm2]

Sp

ec

-E r

R [

g/c

m2]

0

0.5

1.0

1.5

2.0

0 0.5 1.0 1.5 2.0

Sp

ec

-E r

R [

g/c

m2]

Spec-A rR [g/cm2]

13

MRS

Spec-E

Spec-A

10-12 MeV 10-12 MeV

Neutron measurements of un-

scattered neutrons also indicate

similar low-mode ρR asymmetries

Johan Frenje – IAEA 2012

Data

When using the 6-10 MeV range, Spec-E and Spec-A nTOFs

probe similar portion of the implosion, and provide similar ρR values

6-10 MeV

Need to address the observed higher-than-predicted levels

of mix and low-mode ρR asymmetries

• Understand the origin and structure of mix and low-mode ρR asymmetries.

• Lower CR implosions (more 1D) should be examined and understood to improve the

modeling capabilities before conducting the high CR implosions necessary for ignition.

• Engineering solutions and new diagnostic capabilities need to be implemented:

– Implement in-flight 2D x-ray radiography of the ablator.

– Implement in-flight Compton radiography of the fuel.

– Implement a new nTOF-neutron spectrometer for probing rR on the south pole.

– Reduce size and/or patch up diagnostic holes and star burst, and reduce diameter of the

fill tube to improve drive symmetry.

14 Johan Frenje – IAEA 2012

Path forward

Summary

The neutron data have been essential to the

progress of the experiments on the NIF

• The neutron-spectrometry data indicate that the tuning campaigns have improved

the implosion performance by ~50× since the 1st shot in Sept 2010.

• We have achieved a radial convergence of ~35, fuel ρR values up to ~1.3 g/cm2,

and inferred hot-spot pressures up to ~150 Gbar.

• The maximum pressure is ~2× lower than point design, and the observed neutron

yields are 3-10× lower than expected.

• The pressure and yield deficits are most likely explained by higher than predicted

fuel-ablator mix and ρR asymmetries often observed in the implosions.

• A path forward to address these issues has been defined.

15

0

2

4

6

8

0 2 4 6 8

Sp

ec

-E d

sr

[%]

Spec-A dsr [%]

In contrast to the 10-12 MeV dsr data, the 6-10 MeV dsr data

show no “rR asymmetries”

6-10 MeV

10-12 MeV

17 Johan Frenje – EPS 2012

Top view

n'

n'

n'

n'

n'

n'

n'

n'

2

21

41' Cos

A

AEE nn

θ

Implosion performance data

A single scattering model cannot explain the low-energy

neutron spectrum in high-rR implosions

MGJ—HTPD 2012 18 5/7/2012

IRF

rR asymmetries and multiple scattering may be important at

energies below 9 MeV, and will be considered

primary

single scatter

MRS data for Cryo DT, Nov. 12, 2011

single scatter

primary

Neutron spectrum simulations indicate that multiple

scatter is important in high rR implosions

MGJ—HTPD 2012 19 5/7/2012

More sophisticated analysis of the neutron

spectrum is currently being developed

rR=2.0 g/cm2

rR=0.2 g/cm2

The MRS measures the neutron spectrum, using the

recoil technique combined with a magnetic spectrometer

Principle

ft

ox

d

rndnd dx

dx

)E(dE

Cos

12CosE9

8E

3-20 MeV (d)

x0

Neutron

(En) r

Deuteron (Ed) tf

nr

CR-39

(5×7cm2)

Implosion

26 cm

570cm

CD-foil n

300 m

400 m

45 tracks

J.A. Frenje et al., Phys. Plasmas 17, 056311 (2010) 20 Johan Frenje – IFSA 2011

The background in the dsr region is determined from DT

exploding pushers, then subtracted to get dsr for DT cryo shots

MGJ—HTPD 2012 21 5/7/2012

10-12 MeV 10-12 MeV

DT Exp Push, Nov. 21, 2011

Cryo DT, Nov. 12, 2011

Spec-A/Spec-E/IgnHi

Time [ns]

dsr = 4.80.4%

Ti=3.490.40 keV

Ti=5.680.64 keV

dsr = 3.90.2%

Ti=3.530.38 keV

Ti=5.350.59 keV

To gain insight about the implosions, a simple

model can be used to infer hot-spot properties from

emitted neutrons, X-rays and g-rays

Hotspot

Y ~ Vol x tburn x <sv> x n2

neutrons g-rays X-rays

Derived hot spot quantities

R

Cold shell

Measured hot spot quantities

Density, r ~ nA

Mass, MHS ~ rV

Pressure, P ~ nT

Energy, E ~ PV

• More sophisticated model

uses isobaric assumption

(n~1/T)

• Allows 3D spatial profiles to

be fit to match all observables

• Time dependence not yet

included

From P. Springer et al., IFSA (2011).