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.

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of M r ∼ −13.4 mag, and was initially classified as a SN impostor. Here we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (∼ 1 yr after). In addition, we inspect archival images of the host galaxy up to ∼ 21 yr before discovery, finding a burst ∼ 1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.

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.