LA-UR-14-24600
High-Energy-Density Physics:
Radiation and Turbulence
F. W. Doss
SSGF Annual Meeting
June 2014
UNCLASSIFIED
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
Acknowledgements
Among the many people who contributed to the work discussed here…
§  LANL P-24: K A Flippo,
J L Kline, T S Perry,
E N Loomis, E Merritt,
J Hager
§  XCP: B. G. DeVolder,
I Tregillis
§  XTD: L Welser-Sherrill,
J Fincke
§  UM: R P Drake,
C C Kuranz, E S Myra,
C DiStefano, B Fryxell,
M J Grosskopf,
C M Krauland,
B van der Holst, A J Visco
§  LLNL: H F Robey,
C M Huntington,
B Remington, H S Park
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High-energy-density (HED) physics allows us to
access new physical processes in terrestrial settings
§  Physics relevant to
extreme events in
astrophysics or fusion
experiments may
depend on effects not
reachable in ordinary
situations.
§  HED experiments are a
way to explore that
physics in a controlled
fashion.
Imploding fuel capsule
ICF implosion image credit K. Flippo
UNCLASSIFIED
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HED experiments are characterized by extreme
conditions typically reached using large facilities
§  10s-100s km/s flow
speeds, Mbar
pressures, nanosecond
timescales.
§  Large laser facilities can
focus 10s of kJ or more
into sub-mm scale
volumes to achieve
HED conditions.
OMEGA Laser, LLE Rochester
§  I will discuss two HED experiments I have been
involved in, at the University of Michigan and at
Los Alamos National Laboratory.
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Shocks are ubiquitous in HED systems due to the
large amounts of energy involved
§  Shocks occur when
supersonic
disturbances or large
energy releases are
introduced into a flow.
T > T0
P > P0
§  Shock physics has
been well understood
under normal conditions
since the 1800s.
ρ > ρ0
Shocks increase the temperature
and density of the fluid they transit
W. J. Macquorn Rankine. On the thermodynamic theory of
waves of finite longitudinal disturbance. Phil. Trans. R. Soc.
Lond., 160:277–288, January 1870
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Increasing shock speeds to 100s of km/s, it becomes
possible to excite radiative effects
§  As shocks become very
strong, the post-shock
temperatures can
become very high, and
radiation can stream
ahead of the shock.
§  This effect is always
present, proportional to
σT4 , but is usually
small because σ is tiny.
T >> T0
P >> P0
σ = Stefan-Boltzmann constant
= 5.67.10-8 in SI units
§  But, a 4th power will always win eventually, and it
will do so spectacularly when it does.
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Physical effect example: asymptotically strong shock
compression in Rankine-Hugoniot
⇢0 Vs = ⇢U
Conservation of mass:
… momentum:
… energy:
⇢0 Vs2 + P0 = ⇢U 2 + P
⇢0 Vs3
⇢U 3
+ ⇢0 V s h 0 =
+ ⇢U h
2
2
Unshocked side
Shocked side
§  Among other results, classical shock hydrodynamics
predicts a maximum increase in density as shocks
become stronger, ⇢
+1
⇢0
!
1
§  This predicts maximum shock compressions of ~4-10.
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When radiation becomes important, a previously
neglected contribution to energy conservation appears
Conservation of mass:
… momentum:
… energy:
⇢0 Vs = ⇢U
⇢0 Vs2 + P0 = ⇢U 2 + P
⇢0 Vs3
⇢U 3
+ ⇢0 V s h 0 =
+ ⇢U h
2
2
Unshocked side
Shocked side
T4
Radiation
§  Putting in this term, which was justifiably neglected in
the 1800s, breaks the previous rigorous result for a
maximum compression, and implies that density can
increase unboundedly.
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The next step is to use lasers to produce a very, very
strong shock
§  UM CRASH targets
for the OMEGA laser
contain Xe gas, have
~600 micron tube
diameters, and are
3 mm long.
§  They are irradiated by
4 kJ of energy to
launch a very strong
shock down the tube.
Acrylic shielding
Xenon gas fill
tube / stalk
Plastic shock tube
Beryllium drive disc
Gold
shielding
F. W. Doss. Structure in Radiative Shock Experiments. PhD
thesis, University of Michigan, 2011.
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The shock travels down the tube at 100+ km/s, and is
imaged by x-ray radiography
§  Dark material is
shocked xenon,
unshocked xenon is
transparent.
§  Shock is Mach 600+
when initially launched
into the tube.
§  Shock has traveled
2000 microns, and
gas has been
compressed to around
100 microns.
Doss et al, High Energy Density Physics 6 157 (2010)
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Shooting a lot of targets, we were able to see
consistently that the HED experiments can compress
beyond the classical limit
20
x
x
x
x
xx
x
xx x
Compression
§  A major challenge
in HED is to get
good statistics on
the effect one is
looking for, since
each shot is
typically slightly
irreproducible and
shots are limited
in quantity.
15
x
10
Classical hydrodynamics
5
0
1
10
100
1000
104
105
Pressure increase over shock
Data from Doss et al, High Energy Density Physics 6 157 (2010)
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106
Slide 11
Shocks can also be used in more intricate flow
arrangements – shear experiments
§  The Kelvin-Helmholtz shear
instability creates billowing
wave profiles when flow
speeds differ across an
interface.
ap.smu.ca : photo credit Brooks Martner, NOAA/ETL
§  Left unchecked, instability
growth eventually develops
into turbulence.
§  The Los Alamos National
Laboratory Shock/Shear
experiment explores this and
other instabilities in complex
target geometries.
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LANL HED S/S project explores turbulent mixing in laser-driven
shock tubes at Ω and NIF through various configurations
60 mg/cc CH
Laser
Laser
Ω Counterpropagating shear geometry
Al/Ti plate
60 mg/cc CH
Mix width measured along line
§  Crossing shocks creates extreme
KH.
§  Top right: edge-on view measures
tracer mix width.
§  Bottom right: transverse view is
used to image developing
turbulence in the tracer plane.
Welser-Sherrill et al HEDP, 9, 3, 496 (2013)
Doss et al Phys Plasmas, 20, 012707 (2013)
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Taking images at different times per shot, we obtain a
history of the evolving shear layer
6 ns
7 ns
10 ns
Center line
12 ns
14 ns
Images from Doss et al., Phys. Plasmas 20, 122704 (2013)
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16 ns
We are comparing this data to simulations in the LANL
Simulations from Doss et al., Phys. Plasmas 20, 012707 (2013)
hydrocode RAGE
6 ns
12 ns
8 ns
14 ns
10 ns
§  Comparisons to the
code calculation
helps underpin
models for late time
instability in ICF
implosions.
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We are seeing hints in the simulation that we may be
entering a new physics region for HED turbulence as well
Inflow
BHR off
BHR: small s0
60
60
Different turbulence
models
BHR: high s0
Temperature (eV)
§  This effect is typically
neglected in normal
aerodynamic settings because
it depends on ρM2, and fast
dense flows are rare.
8080
Temperature (eV)
§  Simulations of the experiments
in the RAGE code suggest a
change in the metal layer
temperature due to thermoturbulence coupling.
4040
2020
No turbulence
0
5
5
10
Time (ns)
10
Time (ns)
15
15
Al plate
60 mg/cc CH
UNCLASSIFIED
Doss et al., Phys. Plasmas 20, 122704 (2013)
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
Inflow
20
20
A NIF variant of the experiment is currently underway
§  With >1 MJ available at NIF, compared to ~10 kJ
at OMEGA, a much larger target can be
constructed.
§  Challenges in going to NIF have included
redesigning the target for indirect drive, adapting
to new diagnostics schemes, and even more
scarce shot rate.
5 mm
Built target
To scale target designs
5 kJ
5 kJ
300 kJ
Omega
300 kJ
NIF
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Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
Summary
§  I have had the fortune to be involved in interesting research
with High-Energy-Density experiments at both UM and
LANL using the OMEGA and NIF laser facilities.
§  The HED experiments are of interest and value for their
ability to access regimes considered beyond traditional
aerodynamics and fluids experiments, shedding light on
processes in extreme systems such as ICF and
astrophysics.
§  However, they must deal with limited data collection rate,
intricate target requirements, advanced modeling
requirements, and obtaining facility time, all of which are
challenges.
UNCLASSIFIED
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA