Blanc SIMI 5 - Blanc - SIMI 5 - Physique subatomique et théories associées, astrophysique, astronomie et planétologie

Opacity calculations and High Energy Laser experimental validation for Stellar Physics – OPACITY

OPACITY

Opacity calculations for Stellar Physics with High Energy Laser experimental validation.<br />This project will improve our knowledge of the absorption interaction of photons with plasmas in the domain of X and XUV for stellar thermodynamical conditions and elements of intermediate Z (typically oxygen) and up to Z = 28 (nickel). It will deliver also to a large international community, qualified opacity calculations for their own use.<br /><br />

CONTEXT, POSITION AND OBJECTIVES OF THE PROPOSAL

This proposal is dedicated to astrophysical questions that we hope to solve:<br />- Is the present discrepancy between observed sound speed and standard solar model sound speed at the base of the convective zone and in the central radiative zone largely or partly due to inaccurate determination of the opacity coefficients? <br />- Was the microscopic diffusion underestimated due to incomplete opacity calculations?<br />The answer to these two questions are important to progress on the dynamics of the solar interior and the formation of stellar system with planets.<br />- Could we better understand massive stars and related seismic observations in improving the opacity calculations of the iron peak?. We shall concentrate in this proposal on the beta Cephei (8-12 solar masses) and the SPB stars (Slowly Pulsating stars (5-7 solar masses) that are on the main sequence.<br />- What is the impact of these calculations on the absolute values of the modes?<br />In parallel, the related efforts will benefit to young researchers who are now formed in plasma physics because the experiments in this field need a lot of expertise.<br />Plasma physics at high temperature (T > 200000 K) and density (up to solid density) is a totally new field in laboratory, so the applications are even not yet imagined.

We have chosen two thermodynamical cases where problems have been identified and that need both immediate investigations on the role of opacity in the solution of these problems.
The first case corresponds to the radiative zone of the Sun or solar like stars for which we observe about 40 acoustic modes for at least 100 stars. The interesting installations are Z machine and new laser installations like ORION and PETAL+LMJ-4 quads that can produce plasmas closer to the local thermodynamical equilibrium (LTE). A first experiment on Z-machine added to other experimental checks on other installations has already qualified some aspect of the OPAS code together with some limitation of the existing codes, a second measurement on Z-machine could give new results this year. The installation of Bordeaux is not yet ready and needs detailed preparation for this huge site. So, due to the excellent observation of the inner Sun by several satellites, the present suspicion on the opacity calculations (figures 5) and the microscopic diffusion treatment, we will use immediately the OPAS effort who have already calculated the 21 elements that enter in the composition of the Sun.
The second case corresponds to lower temperature and density that can be checked in LULI2000, this case has already conducted us to perform experiments near this installation so the present measurements have to be analysed and compared to calculations. The first action will be to estimate the quality of the experiments and of our related opacity calculations coming from mainly the 3 French groups: OPAS, SCO-RCG, HULLAC. Other comparisons will be done with Los Alamos team, the English team and the academic OP new results. In these thermodynamical conditions, our objective will be to replace some incomplete absorption spectra and mean Rosseland values by more complete calculation for elements of the iron group and estimate the consequences of the progress.

Our scientific aim is to perform new opacity calculations useful for two communities: the stellar community and the fusion community.
In the two mentioned thermodynamical conditions, our objective will be to replace some incomplete absorption spectra and mean Rosseland values by more complete calculation for elements of the iron group and estimate the consequences of the progress.

Improvements of the understanding of the helio and asteroseismic observations.

 

This project has the aim to improve our knowledge of the absorption interaction of photons with plasmas in the domain of X and XUV for stellar thermodynamical conditions. This knowledge is extremely useful for fusion science, atomic physics and astrophysics as it governs the energy transfer in hot plasmas. This project will specifically answer to different questions suggested by the international community of stellar physics through helioseismic and asteroseismic investigation of thousand of stars (space missions SoHO, COROT and KEPLER) for elements of intermediate Z (typically oxygen) and up to Z = 28 (nickel).
This project will deliver also to a large international community, qualified opacity calculations for their own use.
We shall concentrate our study on specific elements (oxygen, silicium, manganese, chromium, iron, nickel, copper…) and two plasma conditions corresponding to the central radiative zones of Sun and solar-like stars (T> 106 K and around solid density) and to the region of the opacity bump of iron in the envelopes of most of the pulsating stars (equivalent ionization conditions corresponding to T around 2 105 K and density of some mg/cm3).
This project has three main parts: (1) Comparison between calculations using different approaches (OPAS, SCO-RCG, HULLAC and OP) to properly determine the role of the different terms of the calculations and to justify some approximations when it is possible. Our calculations are also confronted to American (OPAL, LEDCOP) and English codes. Then we shall perform specific calculations for stellar physics. (2) Validation by some specific experiments performed on LULI2000 lasers at Polytechnique for the lowest temperature conditions. Within the three years of the OPACITY project, the calibration of the XUV spectrometer used in Polytechnique will be done and a high resolution X spectrometer prototype will be performed for experiments on LULI2000. In parallel simulations of experiments with PETAL+ LMJ lasers in Bordeaux, for the highest temperatures, will be realised that could imply some actions on ORION facility in England. A specification document for a high-resolution X spectrometer + camera in Bordeaux will be prepared. These experimental activities will conduct to an opacity proposal in response to the call for academic participation to PETAL+4quads LMJ in 2014 or 2015 (3) Specific new opacity calculations for stellar physics will be introduced in stellar codes and the consequences for stellar evolution and stellar pulsations examined. The new validated physics will be delivered to the international stellar community at the end of this project. This work could conduct to some other deliveries on requests (magnetic or inertial fusion for energy).
Since the creation of the OPAC consortium four years ago, a lot of activities have been already performed within the consortium. This allows us to be immediately operational to attack the different aspects of the proposal: calculations and measurements have been already realized; members of the consortium already publish some of them. These actions demonstrate the maturity of the French team, which is internationally well placed to attack the different described problems in the best conditions: number of participants and expertise.

Project coordination

Sylvaine TURCK-CHIÈZE (Commissariat à l'énergie atomique et aux énergies alternatives) – sylvaine.turck-chieze@cea.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CELIA UMR 5107 Centre lasers intenses et applications
CEA/DAM Commissariat à l'énergie atomique et aux énergies alternatives
CEA/IRFU/SAp Commissariat à l'énergie atomique et aux énergies alternatives

Help of the ANR 575,884 euros
Beginning and duration of the scientific project: December 2012 - 36 Months

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