# Presentation: 561616

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

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

- Thanks to:
**James E. Bailey, Sandia National Laboratories (jebaile@sandia.gov)**

- 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 + Mg**

**without Fe**

**Warm Dense Matter Winter School**
**Lawrence 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 

-  **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**

## Modern solar models disagree with observations. Why? 

**  ****R****CZ**** = 0.713 **_**+**_** 0.001**
** ****Predicted R****CZ****= 0.726**
** ****Thirteen ******** difference**

** ****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.**

**T****e**

**n****e**

**Modern solar models disagree with observations. Why? **

## Transitions in Fe with L shell vacancies influence the radiation/convection boundary opacity

**Transitions in Fe with L shell vacancies influence the radiation/convection boundary opacity**

- opacity (cm2/g)

- intensity (1010 Watts/cm2/eV)

- h (eV)

- 1000

- 1400

- 600

- 200

- M-shell

- b-f
- (excited states)

- L-shell

- 104

- 106

- 0

- 1

- 2

- 103

- 104

- 2

- 4

- 0

**solar interior**
**182 eV, 9x10****22**** cm****-3**

**Z conditions**
**155 eV, 1x10****22**** 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:_
- 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

## Anatomy of an opacity experiment

- Comparison of unattenuated and attenuated spectra determines transmission
**T = 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**

**CH****2**** foam**

**radiating shock**

**capsule**

- gated
- X-ray
- camera

- 1 nsec
- snapshots

**radiating shock**

## The  radiation source heats and backlights the sample 

## The dynamic hohlraum backlighter measures transmission over a very broad  range

- (Angstroms)

- transmission

- Fe
- L-shell

- Z1363-1364
- Fe+Mg
- sample

- bound-free

- Mg
- K-shell

## Samples consist of Fe/Mg mixtures fully tamped with 10 m 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**

## Z opacity experiments reach T ~ 156 eV, two times higher than in prior Fe research

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

**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 

## The transmission is reproducible from shot to shot

**The transmission is reproducible from shot to shot**

**7**

**9**

**11**

**12**

- (Angstroms)

- Intensity

- Z1650
- Z1649

**8**

**10**

## Multiple reproducible experiments enables averaging to improve transmission S/N

- (Angstroms)

**Multiple reproducible experiments enables averaging to improve transmission S/N**

- Fe
- L-shell

- Z1466,1467,1646,1648,1649,1650,1651,1652,1653
- Fe+Mg

- Mg
- K-shell

- transmission

- 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 CH****2**** plasma)**