(1) Iron opacity measurements on Z at 150 eV temperatures

1
(1)Iron opacity measurements on Z at 150 eV
temperatures

• Thanks to
• James E. Bailey, Sandia National Laboratories
  (jebaile_at_sandia.gov)

with Fe Mg
without Fe
Warm Dense Matter Winter School Lawrence Berkeley
National Laboratory January 10-16, 2008
Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin
Company,for the United States Department of
Energys National Nuclear Security
Administration under contract DE-AC04-94AL85000.
2
Wavelength-dependent opacity governs radiation
transport that is critical in HED plasmas

• Bound-bound and bound free transitions in mid to
  high Z elements dominate opacity
• As Z grows, the number of transitions becomes
  enormous
• ( 1-100 million line transitions in typical
  detailed calculations)
• Approximations are required and experimental
  tests are vital
• Example 1 Solar interior
• Example 2 Cu-doped Be ablator ICF capsule

3
Radiation controls heat transport in solar
interior

• boundary position depends on transport
• measured with helioseismology

Solar model J.N. Bahcall et al, Rev. Mod. Phys.
54, 767 (1982)
convection
radiation
Transport depends on opacity, composition, ne, Te
4
Modern solar models disagree with observations.
Why?

• measured boundary
• RCZ 0.713 0.001
• Predicted RCZ 0.726
• Thirteen s difference

ne
Te

• Boundary location depends on radiation transport
• A 1 opacity change leads to observable RCZ
  changes.
• This accuracy is a challenge experiments are
  needed to know if the solar problem arises in the
  opacities or elsewhere.

5
Transitions in Fe with L shell vacancies
influence the radiation/convection boundary
opacity
solar interior 182 eV, 9x1022 cm-3
M-shell
4
105
b-f (ground states)
b-f (excited states)
104
2
103
L-shell
opacity (cm2/g)
0
intensity (1010 Watts/cm2/eV)
Z conditions 155 eV, 1x1022 cm-3
106
2
105
104
1
103
0
1000
1400
600
200
hn (eV)
6
Cu dopant is intended to control radiation flow
into Be ICF capsule ablator

• Pre-heat suppression requires opacity knowledge
  in the 1-3 keV photon energy range
• Tailoring the ablation front profile requires
  opacity knowledge in vicinity of Planckian
  radiation drive maximum
• Cu transitions that influence the opacity are
  very similar to the Fe transitions that control
  solar opacity near the radiation/convection
  boundary

7
Goal of opacity experiments test the physics
foundations of the opacity models

• Agreement at a single Te/ne value is difficult,
  but not sufficient
• It is impractical to perform experiments over the
  entire Te/ne range
• Therefore we seek to investigate individual
  processes
• charge state distribution
• Term structure needed? Fine structure?
• Principal quantum number range
• Bundling transitions into unresolved arrays
• Multiply excited states
• Low probability transitions (oscillator strength
  cut off)
• Bound free cross sections
• Excited state populations
• Line broadening

8
Anatomy of an opacity experiment
Comparison of unattenuated and attenuated spectra
determines transmission T exp mrx Model
calculations of transmission are typically
compared with experiments, rather than opacity.
This simplifies error analysis.
9
Dynamic hohlraum radiation source is created by
accelerating a tungsten plasma onto a low Z foam
gated X-ray camera
1 nsec snapshots
radiating shock
CH2 foam
radiating shock
capsule
tungsten plasma
4 mm
10
The radiation source heats and backlights the
sample
11
The dynamic hohlraum backlighter measures
transmission over a very broad l range
Z1363-1364 FeMg sample
transmission
bound-free
Mg K-shell
Fe L-shell
l (Angstroms)
12
Samples consist of Fe/Mg mixtures fully tamped
with 10 mm CH

• Fe Mg coated in alternating 100-300 Angstrom
  layers
• CH tamper is 10x thicker than in typical laser
  driven experiments
• Compare shots with and without Fe/Mg to obtain
  transmission
• Mg serves as thermometer and density diagnostic

13
Z opacity experiments reach T 156 eV, two times
higher than in prior Fe research
J.E. Bailey et al., PRL 99, 265002 (2007)

• Mg is the thermometer, Fe is the test element
• Mg features analyzed with PrismSPECT, Opal, RCM,
  PPP, Opas

14
Modern detailed opacity models are in remarkable
overall agreement with the Fe data
15
The transmission is reproducible from shot to shot
Z1650 Z1649
Intensity
7
9
11
12
8
10
l (Angstroms)
16
Multiple reproducible experiments enables
averaging to improve transmission S/N
Z1466,1467,1646,1648,1649,1650,1651,1652,1653 FeM
g
1.0
0.8
0.6
transmission
0.4
0.2
Mg K-shell
Fe L-shell
0.0
l (Angstroms)
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Conclusions of present work

• The excellent agreement between PRISMSPECT and
  the measurements demonstrates a promising degree
  of understanding for both modeling and
  experiments
• Comparisons with the Los Alamos ATOMIC/MUTA and
  OPAL are just as good, if not better.
• Modern DTA opacity models are accurate, if
  sufficient attention is paid to setting up and
  running the code.
• With an accurate model in hand, the accuracy
  penalty imposed by various approximations used in
  applications can be investigated
• The Z dynamic hohlraum opacity platform is
  capable of accurate measurements in an important
  and novel regime

18
Future evaluate impact of present data on solar
models and design higher density experiments

• Question Can this work tell us whether prior
  solar opacities were accurate to better than 20?
• Construct Rosseland and Planck mean opacities
• Compare
• Data to modern detailed models
• Data to prior models used in solar application
• Modern models to prior models (extend hn range)
• With reasonable understanding for this class of
  L-shell transitions, now we are ready for new
  experiments
• Increase density
• Alter sample composition (e.g., Fe O in CH2
  plasma)