[en] We propose a hybrid approach to treating atomic structure and rates in collisional-radiative models, combining the completeness of highly averaged models with the accuracy of detailed models. The hybrid scheme supplements a small subset of coronally accessible fine structure levels with a complete set of configuration- and superconfiguration-averaged levels and produces spectra based on transitions among a mix of fine-structure and relativistic configuration-averaged levels. Convenient expressions are given for obtaining rates between the fine structure and averaged levels and a technique for propagating configuration interaction from the fine structure calculations to configuration averages is described. We present results from a trial hybrid model of germanium which demonstrate the accuracy of the hybrid model for charge state distributions and spectra

[en] We report measurements of the line polarization of Ne-like and F-like of iron n=3 to n=2 transitions in the x-ray region. We used the ''two-crystal technique'' developed in previous polarization measurements in our laboratory. Preliminary results from our measurements are presented together with the theoretical calculations using the Flexible Atomic Code (FAC). Our calculations show that contributions from cascades play an important role in the polarization calculations of most of the transitions. The uncertainties and difficulties of our experiments are also discussed

[en] The intensity ratios of 3 → 2 emission lines of Fe XVIII and Ni XX were measured on the Livermore electron beam ion trap (EBIT-I) with a flat-field grating spectrometer. The results were compared with distorted-wave (DW) calculations obtained with the Flexible Atomic Code and recent close-coupling calculations using the R-matrix code. The measured 3s → 2p/3d → 2p ratios are about 20-40% higher than the theoretical values. When more extended configuration interaction is included in the DW theory, the agreement with the measurements improved slightly. At the beam energies of these measurements, no significant resonance contribution is expected to be present, and the discrepancies represent the uncertainties in the direct excitation cross sections

[en] We are continuing EBIT measurements of line lists in the EUV region for use as astrophysical diagnostics and have recently measured the same transitions in much denser plasma of the NSTX tokamak. This allows us to calibrate density-sensitive line ratios at their upper limits. We compare our observations at low and high density with calculations from the Flexible Atomic Code

[en] We present a comprehensive wavelength survey of Fe L-shell X-ray lines between 7 and 11 (angstrom) measured using flat crystal spectrometers and the EBIT-I and EBIT-II electron beam ion traps at the Lawrence Livermore National Laboratory. This survey includes all significant emission lines produced by over 200 n → 2 transitions in Fe XIX-XXIV, with n = 4-10. The identification and assignment of transitions are made with the help of detailed theoretical modeling using the Flexible Atomic Code (FAC)

[en] The electric quadrupole (E2) and magnetic octupole (M3) ground-state transitions in Ni-like W⁴⁶⁺ have been measured using high-resolution crystal spectroscopy at the LLNL electron-beam ion trap facility. The lines fall in the soft x-ray region near 7.93 A and were originally observed as an unresolved feature in tokamak plasmas. Using flat ammonium dihydrogen phosphate and quartz crystals, the wavelengths, intensities, and polarizations of the two lines have been measured for various electron-beam energies and compared to intensity and polarization calculations performed using the Flexible Atomic Code (FAC).

[en] In this tutorial, we will discuss practical usage of the Flexible Atomic Code (FAC) for intermediate users. Basic knowledge of atomic physics and plasma spectroscopy is assumed, but familiarity with FAC in particular is not required. The topics covered in the tutorial include: • Download and installation. • Atomic processes implemented in FAC. • SFAC and PFAC interfaces. • Handling FAC binary and ascii output files. • Basic usage for simple atomic systems. • Coupling atomic calculations and collisional radiative modeling. • Advanced features: Many-body perturbation theory and R-Matrix. We will follow the tutorial through several practical examples, both simple and more advanced. Simple examples will demonstrate the use of FAC in obtaining limited sets of atomic parameters, such as energy levels, radiative rates, and collisional cross sections. More complex examples will demonstrate the use of PFAC interface (via the Python scripting language) to generate large scale datasets, and use them as input to collisional radiative models for spectroscopic modeling applications.

[en] We present detailed atomic physics models for the motional Stark effect (MSE) diagnostic on magnetic fusion devices. Excitation and ionization cross sections of the hydrogen or deuterium beam travelling in a magnetic field in collisions with electrons, ions and neutral gas are calculated in the first Born approximation. The density matrices and polarization states of individual Stark-Zeeman components of the Balmer α line are obtained for both beam into plasma and beam into gas models. A detailed comparison of the model calculations and the MSE polarimetry and spectral intensity measurements obtained at the DIII-D tokamak is carried out. Although our beam into gas models provide a qualitative explanation for the larger π/σ intensity ratios and represent significant improvements over the statistical population models, empirical adjustment factors ranging from 1.0 to 2.0 must still be applied to individual line intensities to bring the calculations into full agreement with the observations. The analyses of the filter-scan polarization spectra from the DIII-D MSE polarimetry system indicate unknown channel and time-dependent light contaminations in the beam into gas measurements. Such contaminations may be the main reason for the failure of beam into gas calibration on MSE polarimetry systems

[en] The line ratios of the 2p-3d transitions in the B-like spectra Ar XIV and Fe XXII have been measured using the electron beam ion traps at Livermore. Radiative-collisional model calculations show these line ratios to be sensitive to the electron density in the ranges ne = 10¹⁰ to 10¹² cm^-3 and ne = 10¹³ to 10¹⁵ cm^-3, respectively. In our experiment, the electron beam density of about 10¹¹ cm^-3 was varied by about a factor of 5. Our data show a density effect for the line doublet in Ar XIV, and good agreement with theory is found. The relative intensity of the Fe XXII doublet shows good agreement with our predicted low density limit. The N VI K-shell spectrum was used to infer the actual electron density in the overlap region of ion cloud and electron beam, and systematic measurements and calculations of this spectrum are presented as well. The Ar XIV and Fe XXII spectra promise to be reliable density diagnostics for stellar coronae, complementing the K-shell diagnostics of helium-like ions

[en] The M-shell x-ray emission of highly charged tungsten ions has been investigated at the Livermore electron beam ion trap facility. Using the SuperEBIT electron beam ion trap and a NASA x-ray calorimeter array, transitions connecting to levels of the ground configurations in the 1500-3600 eV spectral range of zinc-like W⁴⁴⁺ through cobalt-like W⁴⁷⁺ have been measured. The measured spectra are compared with theoretical line positions and emissivities calculated using the FAC code.