Nearly a century ago it was recognized that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models. A particular problem arose when refined photosphere spectral analysis led to reductions of 30-50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9-2.3 million kelvin and electron densities of (0.7-4.0) × 10(22) per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30-400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

HELIOS-CR is a user-oriented 1-D radiation-magnetohydrodynamics code to simulate the dynamic evolution of laser-produced plasmas and z-pinch plasmas. It includes an in-line collisionalradiative (CR) model for computing non-LTE atomic level populations at each time step of the hydrodynamics simulation. HELIOS-CR has been designed for ease of use, and is well-suited for experimentalists, as well as graduate and undergraduate student researchers. The energy equations employed include models for laser energy deposition, radiation from external sources, and high-current discharges. Radiative transport can be calculated using either a multi-frequency flux-limited diffusion model, or a multi-frequency, multi-angle short characteristics model. HELIOS-CR supports the use of SESAME equation of state (EOS) tables, PROPACEOS EOS/multi-group opacity data tables, and non-LTE plasma properties computed using the inline CR modeling. Time-, space-, and frequency-dependent results from HELIOS-CR calculations are readily displayed with the HydroPLOT graphics tool. In addition, the results of HELIOS simulations can be post-processed using the SPECT3D Imaging and Spectral Analysis Suite to generate images and spectra that can be directly compared with experimental measurements. The HELIOS-CR package runs on Windows, Linux, and Mac OSX platforms, and includes online documentation. We will discuss the major features of HELIOS-CR, and present example results from simulations.

Measurements of iron-plasma transmission at 156+/-6 eV electron temperature and 6.9+/-1.7 x 10(21) cm(-3) electron density are reported over the 800-1800 eV photon energy range. The temperature is more than twice that in prior experiments, permitting the first direct experimental tests of absorption features critical for understanding solar interior radiation transport. Detailed line-by-line opacity models are in excellent agreement with the data.

We have studied the K-shell emission of an Al plasma which was generated by focusing a high contrast 150 fs laser pulse at a wavelength of 395 nm and intensity of 5 3 10 17 W͞cm 2 on a flat Al target tamped by a thin surface layer of MgO. The measured resonance lines (Ly a , He a , and He b ) and their Li-like and He-like satellites are extremely broadened and show a red polarization shift. Analysis of the Ly a and He b satellites yields an electron temperature of ഠ300 eV and an electron density of ͑5 10͒ 3 10 23 cm 23 . [S0031-9007(99)09405-3] PACS numbers: 52.50. Jm, 52.25.Nr, 52.70.Kz One fascinating aspect of the interaction of intense, ultrashort-duration laser pulses with matter is the possibility to generate plasmas at solid state density at high temperatures in the range 0.1 to 1 keV. Under these conditions the ion coupling parameter G [1] exceeds one and the plasma is thus in a strongly coupled state [2]. Such plasmas are of particular interest in inertial confinement fusion (ICF) and astrophysics. For example, it is possible to study the x-ray opacity of matter under conditions found in stellar interiors [3]. The importance for ICF originates from the fact that fs-laser generated plasmas approach temperatures and densities similar to the values currently attained in indirect drive experiments [4] and may therefore be of interest to investigate x-ray spectroscopy diagnostics needed for ICF plasmas [5]. In contrast to ICF plasmas, which require huge laser facilities, fs-laser plasmas can be generated by small tabletoplike lasers with a high repetition rate.Here we report an experiment in which we focused a frequency doubled 150-fs Ti-Sapphire laser on tamped targets, which consisted of solid Al covered by a thin surface layer of MgO. We measured the Al K-shell emission by means of time-integrated high resolution crystal spectroscopy. The resonance and satellite lines were considerably broader than previously reported [6][7][8][9]. For the detailed spectral analysis, we used simultaneously the He-like satellites of the Ly a line and the He b line which is strongly merged with its Li-like satellites. To our knowledge these features have not been considered in previous studies of the x-ray emission from fs-laser plasmas. Our analysis indicates that we achieved a higher density compared to previous experiments where the electron density did not exceed a few times 10 23 cm 23 . We attribute this result to the fact that we avoided early expansion by using a high contrast fs-laser pulse and tamped targets. Also the short wavelength of 395 nm may be helpful because it leads to absorption of the laser at a high critical density (n c 7.2 3 10 21 cm 23 ). Altogether, it was thus possible to produce ultrafast heating of solid Al before any significant expansion took place (i.e., isochoric heating).The ATLAS Ti-Sapphire laser at the MPQ-Garching was used to produce pulses with 150 fs (FWHM), and 200 mJ at l 790 nm. To achieve a high contrast ratio, we frequency doubled the pulses and obtained 65-75 mJ at l 395 nm. ...

Theoretical opacities are required for calculating energy transport in plasmas. In particular, understanding stellar interiors, inertial fusion, and Z pinches depends on the opacities of mid-atomic-number elements over a wide range of temperatures. The 150–300 eV temperature range is particularly interesting. The opacity models are complex and experimental validation is crucial. For example, solar models presently disagree with helioseismology and one possible explanation is inadequate theoretical opacities. Testing these opacities requires well-characterized plasmas at temperatures high enough to produce the ion charge states that exist in the sun. Typical opacity experiments heat a sample using x rays and measure the spectrally resolved transmission with a backlight. The difficulty grows as the temperature increases because the heating x-ray source must supply more energy and the backlight must be bright enough to overwhelm the plasma self-emission. These problems can be overcome with the new generation of high energy density (HED) facilities. For example, recent experiments at Sandia’s Z facility [M. K. Matzen et al., Phys. Plasmas 12, 055503 (2005)] measured the transmission of a mixed Mg and Fe plasma heated to 156±6 eV. This capability will also advance opacity science for other HED plasmas. This tutorial reviews experimental methods for testing opacity models, including experiment design, transmission measurement methods, accuracy evaluation, and plasma diagnostics. The solar interior serves as a focal problem and Z facility experiments illustrate the techniques.

SPECT3D is a multi-dimensional collisional-radiative code used to post-process the output from radiation-hydrodynamics (RH) and particle-in-cell (PIC) codes to generate diagnostic signatures (e.g., images, spectra) that can be compared directly with experimental measurements. This ability to postprocess simulation code output plays a pivotal role in assessing the reliability of RH and PIC simulation codes and their physics models. SPECT3D has the capability to operate on plasmas in 1-D, 2-D, and 3-D geometries. It computes a variety of diagnostic signatures that can be compared with experimental measurements, including: time-resolved and time-integrated spectra, space-resolved spectra and streaked spectra; filtered and monochromatic images; and x-ray diode signals. Simulated images and spectra can include the effects of backlighters, as well as the effects of instrumental broadening and time-gating. SPECT3D also includes a drilldown capability that shows where frequency-dependent radiation is emitted and absorbed as it propagates through the plasma towards the detector, thereby providing insights on where the radiation seen by a detector originates within the plasma. SPECT3D has the capability to model a variety of complex atomic and radiative processes that affect the radiation seen by imaging and spectral detectors in high energy density physics (HEDP) experiments. LTE (local thermodynamic equilibrium) or non-LTE atomic level populations can be computed for plasmas. Photoabsorption rates can be computed using either escape probability models or, for selected 1-D and 2-D geometries, multi-angle radiative transfer models. The effects of non-thermal (i.e., non-Maxwellian) electron distributions can also be included. To study the influence of energetic particles on spectra and images recorded in intense short-pulse laser experiments, the effects of both relativistic electrons and energetic proton beams can be simulated.SPECT3D is a user-friendly software package that runs on Windows, Linux, and Mac platforms.A parallel version of SPECT3D is supported for Linux clusters for large-scale calculations. We will discuss the major features of SPECT3D, and present example results from simulations and comparisons with experimental data.

Experimental tests are in progress to evaluate the accuracy of the modeled iron opacity at solar interior conditions, in particular to better constrain the solar abundance problem [S. Basu and H.M. Antia, Physics Reports 457, 217 (2008)]. Here we describe measurements addressing three of the key requirements for reliable opacity experiments: control of sample conditions, independent sample condition diagnostics, and verification of sample condition uniformity. The opacity samples consist of iron/magnesium layers tamped by plastic. By changing the plastic thicknesses, we have controlled the iron plasma conditions to reach i) T e =167±3 eV and n e = (7.1 ± 1.5) × 10 21 cm −3 , ii) T e =170±2 eV and n e = (2.0 ± 0.2) × 10 22 cm −3 , and iii) T e =196±6 eV and n e = (3.8 ± 0.8) × 10 22 cm −3 , which were measured by magnesium tracer K-shell spectroscopy. The opacity sample non-uniformity was directly measured by a separate experiment where Al is mixed into the side of the sample facing the radiation source and Mg into the other side. The iron condition was confirmed to be uniform within their measurement uncertainties by Al and Mg K-shell spectroscopy. The conditions are suitable for testing opacity calculations needed for modeling the solar interior, other stars, and high energy density plasmas.

Direct-drive-implosion core conditions have been characterized on the 60-beam OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system with time-resolved Ar K-shell spectroscopy. Plastic shells with an Ar-doped deuterium fill gas were driven with a 23 kJ, 1 ns square laser pulse smoothed with 1 THz smoothing by spectral dispersion (SSD) and polarization smoothing (PS) using birefringent wedges. The targets are predicted to have a convergence ratio of ∼15. The emissivity-averaged core electron temperature (Te) and density (ne) were inferred from the measured time-dependent Ar K-shell spectral line shapes. As the imploding shell decelerates the observed Te and ne increase to 2.0 (±0.2) keV and 2.5 (±0.5)×1024 cm−3 at peak neutron production, which is assumed to occur at the time of the peak emissivity-averaged Te. At peak compression the ne increases to 3.1 (±0.6)×1024 cm−3 and the Te decreases to 1.7 (±0.17) keV. The observed core conditions are close to those predicted by a one-dimensional hydrodynamics code.