INERTIAL-CONFINEMENT FUSION AT LOS ALAMOS

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INERTIAL-CONFINEMENT FUSION AT LOS ALAMOS
LA-UR-05-0494

• Erick Lindman
• Los Alamos National Laboratory
• Los Alamos, NM 87545, USA
• To be presented to the
• 6th Symposium on Current Trends in International
  Fusion Research, A Review
• Washington, D.C., USA
• 7 - 11 March 2005

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Inertial-Confinement Fusion at Los Alamos

• Beryllium Microstructure, Shock Waves and
  Stability
• N.M. Hoffman, J.A. Cobble, D.L. Tubbs, D.C. Swift
  and T.E. Tierney (LANL)
• X-ray Phase-Contrast Imaging in ICF and HEDP
  Experiments
• D.S. Montgomery (LANL) and B.J. Kozioziemski
  (LLNL)
• Laser-Driven Ion Beams
• M. Hegelich, B. Albright, J. Cobble, C. Gauthier,
  R. Johnson, S. Letzring, T. Ortiz and J.
  Fernandez (LANL)
• Gas-Filled Hohlraum Experiments at the National
  Ignition Facility
• J.C. Fernandez, C. Gautier, S.R. Goldman,G.
  Grimm, M. Hegelich, J. Kline, D.S. Montgomery, N.
  Lanier, H. Rose, D. Schmidt, D.C. Swift and J.
  Workman (LANL) S. Alvarez, D. Bower, D.
  Braun, K. Campbell, E. DeWald, S. Glenzer, J.
  Holder, J. Kamperschroer, J. Kimbrough, B.
  Kirkwood, O. Landen, T.McCarville, B. MacGowan,
  A. MacKinnon, J. McDonald, C. Niemann, J. Schein,
  M. Schneider, P. Watts and B. Young (LLNL)

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Many metals have polycrystalline microstructure
in their initial state.
Optical metallograph of hot isostatically pressed
Be(0.9Cu) alloy A. Nobile et al.,
Fabrication and Characterization of Targets for
Shock Propagation and Radiation Burnthrough
Measurements on beryllium-0.9 at copper alloy,
LA-UR-03-5310, July 2003

• We often ignore microstructure in simulations of
  laboratory HEDP experiments
• But is this valid if first shock is 1 Mbar?

X-1 Plasma Physics
Applied Physics Division
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Detailed calculation of shock interaction with
grain boundary shows generation of transverse
velocity.

• Finite-volume code using continuum material
  model with explicit elastic and plastic
  anisotropy
• Only primary slip systems active
• 0.32-Mbar shock wave in cubic NiAl bicrystal
• Result transverse velocity 5 vshock is
  generated

(transverse velocity)
cm/s
D.R. Greening and A. Koskelo, Calculation of
Grain Boundary Shock Interactions,
LA-UR-03-4909, Proc. APS SCCM Conf., July 2003
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Recent computational advances reveal fluctuating
velocity field behind shock wave in
polycrystalline material.
Longitudinal Velocity Fluctuations in Shock
Compression of Polycrystalline ?-Iron

Ps 5.5 GPa
V/V0
Ps 12 GPa
Ps 45 GPa
Y. Horie and K. Yano, Particle Velocity
Fluctuations in the Shock Compression of Solids,
LA-13936-MS, May 2002
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Maximum velocity fluctuation occurs for 100 Gpa
(1 Mbar) shock, with amplitude 2 of shock
velocity.
D.C. Swift et al., Predictions of the
Microstructural Contribution to Instability
Seeding in Beryllium ICF Capsules,
LA-UR-03-5675, July 2003
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Microstructure-induced velocity fluctuations may
be dangerous for NIF ignition capsules, which are
highly unstable.

• Growth rate for ablative Rayleigh-Taylor
  instability is roughly

where g shell acceleration, k perturbation
wavenumber, va velocity of ablation front, b 2
h ? (b x fraction of shell ablated)/(shell
compression factor x initial shell aspect ratio)
2 x 0.5 / 4 x 6.25 1/25 Fastest-growing mode
mmax 1/4h2 150 has growth (gt)max 1/4h
6.3 6.3 e-foldings means growth factor 540
Further growth during deceleration leads to
total growth factor 1000
H. Takabe et al., Phys. Fluids 28, 3676 (1985)
R. Betti et al., Phys. Plasmas 3, 2122 (1996)
Phys. Plasmas 2, 3844 (1995) J. D. Lindl,
Inertial Confinement Fusion, Springer-Verlag,
1998.
X-1 Plasma Physics
Applied Physics Division
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Embedded single-mode velocity fluctuation causes
perturbation growth that matches growth from
surface displacement.
Velocity perturbation of 103 cm/s matches surface
perturbation with 0.0064 mm amplitude For
incompressible Rayleigh-Taylor instability,
Thus
In this simulation
X-1 Plasma Physics
Applied Physics Division
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The seeding of Rayleigh-Taylor instabilities by
velocity perturbations from the interaction of a
shock with beryllium microstructure is under
study.

• Many metals including beryllium have
  polycrystalline microstructure (grains) in the
  initial state.
• Transverse velocities are generated when a shock
  interacts with these grain boundaries.
• The flow field behind the shock then contains a
  fluctuating velocity component.
• The fluctuating velocities can seed
  Rayleigh-Taylor directly.
• In Rayleigh-Taylor simulations, a velocity
  perturbation of 103 cm/s matches a surface
  perturbation with 0.0064 ?m amplitude.
• This effect is not included in our design
  calculations and must be evaluated separately.

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Inertial-Confinement Fusion at Los Alamos

• Beryllium Microstructure, Shock Waves and
  Stability
• N.M. Hoffman, J.A. Cobble, D.L. Tubbs, D.C. Swift
  and T.E. Tierney (LANL)
• X-ray Phase-Contrast Imaging in ICF and HEDP
  Experiments
• D.S. Montgomery (LANL) and B.J. Kozioziemski
  (LLNL)
• Laser-Driven Ion Beams
• M. Hegelich, B. Albright, J. Cobble, C. Gauthier,
  R. Johnson, S. Letzring, T. Ortiz and J.
  Fernandez (LANL)
• Gas-Filled Hohlraum Experiments at the National
  Ignition Facility
• J.C. Fernandez, C. Gautier, S.R. Goldman,G.
  Grimm, M. Hegelich, J. Kline, D.S. Montgomery, N.
  Lanier, H. Rose, D. Schmidt, D.C. Swift and J.
  Workman (LANL) S. Alvarez, D. Bower, D.
  Braun, K. Campbell, E. DeWald, S. Glenzer, J.
  Holder, J. Kamperschroer, J. Kimbrough, B.
  Kirkwood, O. Landen, T.McCarville, B. MacGowan,
  A. MacKinnon, J. McDonald, C. Niemann, J. Schein,
  M. Schneider, P. Watts and B. Young (LLNL)

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Phase contrast imaging opens new avenues for
x-ray imaging since you dont need absorption
contrast
For over 100 years, x-ray imaging relied on
absorption to get contrast Many interesting
objects are transparent to x-rays (soft tissue,
low-Z ICF targets, low-Z dense plasmas, etc)
How does one image an object opaque to visible
light, but transparent to x-rays?
NIF Be cryogenic capsule
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Physical concepts of x-ray phase contrast imaging

• Refractive index for x-rays
• n 1 - d ib
• is the phase modulation (d few 10-6 for Be or
  H)
• b is the local attenuation

x
image plane
object plane
the field u(x,y, z0) propagates for z gt
0 according to the Helmholtz Eq
-R1
z
y
R2
z0
Common everyday examples lens random
phase plate Zernike phase contrast µscope
phase variations manifest as amplitude variations
after the wave has propagated (via refraction and
interference) Solution of Helmholtz Eq. for
u(zR2) given by a Rayleigh-Sommerfeld integral
(Fresnel integral)
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This is all fine and dandy for plane waves, what
about spherical waves (a point source)?
x
image plane
object plane
-R1
z
y
R2
z0
can be treated same as coherent plane waves
accounting for M
More general, reverts to plane-wave case when
R1gtgtR2 (M 1)
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Simulated x-ray phase contrast images easily show
DT ice layer perturbations along a great circle
a0 5 µm
Source to object 10 cm Object to detector 90
cm Mag 10 1024 x 1024 detector 20 x 20 µm
pixels 10 keV x-rays 5 µm source size
Be outer surface
a0 2 µm
Be / DT ice interface
inner DT ice surface
a0 0 µm
r0 770 µm m 30 (mode number)
Future theoretical studies to include realistic
2-D perturbations, detector noise models, and
image processing algorithms to retrieve perturbati
on spectrum
D.S. Montgomery et al., RSI 75, 3986 (2004)
B. Kozioziemski et al., in press (2004)
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LLNL has obtained initial experimental results
with phase contrast imaging in Be/Cu cryogenic DT
capsules
Fill tube
Expt. profile
Solid D-T surface
LANL model
Optically opaque beryllium capsule
DT surface made observable by phase contrast
LANL modeling accounts for paraxial wave
propagation complex indices n 1 - d ib,
compound matl. 3-D target geometry (thin
object approx.) energy dependent detector
response spectral weighting finite
x-ray source size
LLNL Calculated W x-ray tube spectrum at 60 kV
B. Kozioziemski et al., EM2.005 Tues. AM
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AWE / LANL / LLNL jet team obtained surprisingly
sharp dynamic radiographs whose features are
consistent with phase contrast imaging
Omega experiment
signature of phase contrast from a phase jump
100 mg/cc carbon foam 3.5 mm OD
expanding shock in foam
Ti jet
Image courtesy of B. Blue, R. Coker, J. Foster,
P. Keiter,T. Perry, P. Rosen, and B. Wilde
Ti washer
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We are pursuing phase-contrast imaging (PCI) to
characterize DT cryo layers in beryllium capsules.

• PCI works like magic, i.e. no special optics is
  required.
• A source with good spatial coherence (plane wave
  or point source) is required.
• A polychromatic source is acceptable.
• Propagation distances specified by the optical
  transfer function are required.
• PCI can be used to detect shock fronts in dynamic
  experiments.
• Some experimental groups have unexpectedly found
  PCI in their point-projection backlit images.
• Smaller sources or larger propagation distances
  are needed to better optimize phase contrast in
  those experiments.

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Inertial-Confinement Fusion at Los Alamos

• Beryllium Microstructure, Shock Waves and
  Stability
• N.M. Hoffman, J.A. Cobble, D.L. Tubbs, D.C. Swift
  and T.E. Tierney (LANL)
• X-ray Phase-Contrast Imaging in ICF and HEDP
  Experiments
• D.S. Montgomery (LANL) and B.J. Kozioziemski
  (LLNL)
• Laser-Driven Ion Beams
• M. Hegelich, B. Albright, J. Cobble, C. Gauthier,
  R. Johnson, S. Letzring, T. Ortiz and J.
  Fernandez (LANL)
• Gas-Filled Hohlraum Experiments at the National
  Ignition Facility
• J.C. Fernandez, C. Gautier, S.R. Goldman,G.
  Grimm, M. Hegelich, J. Kline, D.S. Montgomery, N.
  Lanier, H. Rose, D. Schmidt, D.C. Swift and J.
  Workman (LANL) S. Alvarez, D. Bower, D.
  Braun, K. Campbell, E. DeWald, S. Glenzer, J.
  Holder, J. Kamperschroer, J. Kimbrough, B.
  Kirkwood, O. Landen, T.McCarville, B. MacGowan,
  A. MacKinnon, J. McDonald, C. Niemann, J. Schein,
  M. Schneider, P. Watts and B. Young (LLNL)

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Ion Acceleration mechanisms
Bulk Target(e.g., CD2)
Surface Layer (e.g., CaF)
- - - - - - - - - - - - - - - -
F7 ion
- - - - - -
- -
e-
D ion
- - - -
Incidentlaser

• III. Target Normal Sheath Acceleration
• Ei 10 x Te
• Electrons penetrate target form dense sheath
  on rear, non-irradiated surface
• Strong electrostatic sheath field ionizes
  surface layer (Eo kT / eld MV/mm)
• Rapid (ps) acceleration in expanding sheath
  produces very laminar ion beam

I.
CD2
III.
II.
I. Thermal expansion Ti 2 x Te
II. Front-surface charge separation Static
limit Ti Te
hegelich_at_lanl.gov
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Challenges in laser-accelerating well controlled
high-Z ion Beams

• Highest Charge-to-Mass ratio is dominantly
  accelerated
• Protons from H2O hydrocarbons get most of the
  energy, no matter what target material is used
• chemical impurities with high binding energies
  (oxides, carbides, ...)
• The dominant charge state is accompanied by a
  multitude of lower charge states
• energy drain
• Complicates analysis in transport and stopping
  experiments
• Complicates injection into accelerators
• Boltzmann-like spectra, showing an exponential
  decrease over a wide range of energies
• Many applications profit from, or even require a
  mono-energetic energy distribution
• Only a fraction of the ions can be used

hegelich_at_lanl.gov
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LANL Trident Shot

• Many layers of RCF exposed are consistent with
  mostly proton acceleration
  to gt 10 MeV
• Similar to results from many laser-facilities
• Nova PW, LULI, Vulcan, Janus, Roth,Th/O34/I,
  15.50h
• The measured emittance of Trident-produced proton
  beams is very low 0.0025 ? mm-mrad _at_ 8MeV.
• Cowan et al., PRL 92, 204801 (2004).

hegelich_at_lanl.gov
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Specific surface conditions may enable us to
reach a new acceleration regime
hegelich_at_lanl.gov
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GA Dimpled Pd Target
Front (convex) view
Back (concave) view
Pd1-10 Stats Ød 421 µm hd 121 µm df 15 µm
2mm
Side view
15 mm
hegelich_at_lanl.gov
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First Shots Proton Beam Imaging
Flat Pd 20 um 1500 lpi mesh
Pd2- 5 1500 lpi mesh
Shot 69
Shot 68
hegelich_at_lanl.gov
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We are pursuing laser acceleration of ion beams
for use in fast ignition and other applications.

• Ions are accelerated by thermal expansion,
  front-surface charge separation and rear-surface
  sheath acceleration.
• The highest charge-to-mass ratio is dominantly
  accelerated.
• If not removed, H ions from surface contaminants
  such as water and hydrocarbons get most of the
  energy.
• The dominant charge state is accompanied by a
  multitude of lower charge states and a range of
  energies is obtained.
• The measured transverse emittance of
  Trident-produced proton beams is very low --
  0.0025 ? mm-mrad at 8 MeV.
• Attempts to focus the ions from a curved surface
  require more work.

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Inertial-Confinement Fusion at Los Alamos

• Beryllium Microstructure, Shock Waves and
  Stability
• N.M. Hoffman, J.A. Cobble, D.L. Tubbs, D.C. Swift
  and T.E. Tierney (LANL)
• X-ray Phase-Contrast Imaging in ICF and HEDP
  Experiments
• D.S. Montgomery (LANL) and B.J. Kozioziemski
  (LLNL)
• Laser-Driven Ion Beams
• M. Hegelich, B. Albright, J. Cobble, C. Gauthier,
  R. Johnson, S. Letzring, T. Ortiz and J.
  Fernandez (LANL)
• Gas-Filled Hohlraum Experiments at the National
  Ignition Facility
• J.C. Fernandez, C. Gautier, S.R. Goldman,G.
  Grimm, M. Hegelich, J. Kline, D.S. Montgomery, N.
  Lanier, H. Rose, D. Schmidt, D.C. Swift and J.
  Workman (LANL) S. Alvarez, D. Bower, D.
  Braun, K. Campbell, E. DeWald, S. Glenzer, J.
  Holder, J. Kamperschroer, J. Kimbrough, B.
  Kirkwood, O. Landen, T.McCarville, B. MacGowan,
  A. MacKinnon, J. McDonald, C. Niemann, J. Schein,
  M. Schneider, P. Watts and B. Young (LLNL)

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On the NIF, we have fielded gas-filled-hohlraum
experiments to study laser-plasma instabilities
(LPI).

• Measurements of the wall motion in the halfraum
  targets were consistent with LASNEX simulations.
• LPI back-scatter results confounded expectations
• Stimulated Brillouin (SBS) dominates Raman (SRS)
  for all gas-fill species tested.
• Measured SBS time-averaged reflectivity values
  are high (32), peak values are even higher.
• SRS and SBS peak while the laser pulse is rising.
• At the onset of high back scatter, plasma
  conditions yield high SBS convective linear gain.
• And the wavelengths of the back-scattered light
  are predicted by linear theory.
• The radiation temperatures in the targets were
  seriously degraded by the high reflectivity.

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