(1) Iron opacity measurements on Z at 150 eV temperatures Thanks to: James E. Bailey, Sandia...
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Transcript of (1) Iron opacity measurements on Z at 150 eV temperatures Thanks to: James E. Bailey, Sandia...
(1)Iron opacity measurements on
Z at 150 eV temperaturesThanks to:
James E. Bailey, Sandia National Laboratories ([email protected])
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration
under contract DE-AC04-94AL85000.
with Fe + Mgwithout Fe
Warm Dense Matter Winter SchoolLawrence Berkeley National Laboratory
January 10-16, 2008
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
Radiation controls heat transport in solar interior
T(eV) ne (cm-3) r/R0
1360 6x1025
293 4x1023
182 9x1022
54 1x1022
radiation convection
• boundary position depends on transport• measured with helioseismology
Solar model : J.N. Bahcall et al, Rev. Mod. Phys. 54, 767 (1982)
Transport depends on opacity, composition, ne, Te
0.55
0.90
0.7133
0
• measured boundary RCZ = 0.713 + 0.001
• Predicted RCZ= 0.726
• Thirteen difference
Bahcall et al, ApJ 614, 464 (2004).Basu & Antia ApJ 606, L85 (2004).
• 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.
convection radiation
R/R0
Te (e
V)
ne
(cm
-3)
0.40.20.0 0.80.6 11022
1023
1024
1025
800
1200
400
0
Te
ne
Modern solar models disagree with observations. Why?
Transitions in Fe with L shell vacancies influence the radiation/convection boundary opacity
opac
ity (
cm2 /
g)
inte
nsity
(10
10 W
atts
/cm
2 /eV
)
h (eV)1000 1400600200
M-shell
b-f (excited states)
L-shell
104
106
0
1
2
103
104
2
4
0
solar interior182 eV, 9x1022 cm-3
Z conditions155 eV, 1x1022 cm-3
b-f (ground states)
105
105
103
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
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:
1. charge state distribution
2. Term structure needed? Fine structure?
3. Principal quantum number range
4. Bundling transitions into unresolved arrays
5. Multiply excited states
6. Low probability transitions (oscillator strength cut off)
7. Bound free cross sections
8. Excited state populations
9. Line broadening
Anatomy of an opacity experiment
tamper (low Z)
sample
heating x-rays
backlighter
spectrometerspectrometer
Comparison of unattenuated and attenuated spectra determines transmissionT = exp –{x}
Model calculations of transmission are typically compared with experiments, rather than opacity. This simplifies error analysis.
Dynamic hohlraum radiation source is created by accelerating a tungsten plasma onto a low Z foam
tungsten plasma
4 mm
CH2 foamradiating shock
capsule
gatedX-ray
camera1 nsec
snapshots
radiating shock
The radiation source heats and backlights the sample
time (nsec)-20 -10 0 10
T (
eV)
0
100
200
300 h > 1 keVbacklightphotons
radiationtemperature
sample
radiationsource
X-rays
The dynamic hohlraum backlighter measures transmission over a very broad range
(Angstroms)
tran
smis
sion
4 6 8 10 12 14
Fe L-shell
Z1363-1364Fe+Mgsample
0.0
0.2
0.4
0.6
0.8
1.0
bound-free
Mg K-shell
Samples consist of Fe/Mg mixtures fully tamped with 10 m CH
backlighter
CH tamper Fe/Mg sample
spectrometer
heating x-rays
spectrometer
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
(Angstroms)
tran
smis
sion
Fe + Mg at Te ~ 156 eV, ne ~ 6.9x1021 cm-3
Fe XVI-XX
Mg XI
8.0 10.0 12.0 14.0
0.4
0.0
0.8
• Mg is the “thermometer”, Fe is the test element
• Mg features analyzed with PrismSPECT, Opal, RCM, PPP, Opas
Fe & Mg sample
radiationsource
X-rays
J.E. Bailey et al., PRL 99, 265002 (2007)
Z opacity experiments reach T ~ 156 eV, two times higher than in prior Fe research
Modern detailed opacity models are in remarkable overall agreement with the Fe data
h (eV)800 900 11001000 1200
Red = MUTAJ. Abdallah, LANL
Red = OPALC. Iglesias, LLNL
Red = PRISMSPECTJ. MacFarlane, PRISM
tran
smis
sio
n
Red = OPASOPAS team, CEA
0
0.4
0.8
0.0
0.4
0.8
0.0
0.4
0.8
0
0.4
0.8
The transmission is reproducible from shot to shot
7 9 11 12(Angstroms)
Inte
nsity
Z1650Z1649
• Both experiments used 10 m CH | 0.3 m Mg + 0.1 m Fe | 10 m CH sample
• No scaling was applied for this comparison
• Reproducibility is not always this extraordinary, but variations are less than approximately +10%
8 10
(Angstroms)
8.0 9.0 13.011.010.07.0 12.0 14.0 15.0
Multiple reproducible experiments enables averaging to improve transmission S/N
Fe L-shell
Z1466,1467,1646,1648,1649,1650,1651,1652,1653Fe+Mg
Mg K-shell
tran
smis
sion
0.4
0.0
0.2
0.6
0.8
1.0
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
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 h 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)