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We have measured the collisional excitation cross sections for the 3d→4f and 3d→5f excitations in Au ions near the Ni-like charge state by using beam plasmas created in the Livermore electron beam ion trap EBIT-I. The cross sections have been experimentally determined at approximately 1, 2 and 3 keV above the threshold energy, ET, for the 3d→4f excitations (ET ∼ 2.5 keV) and at approximately 0.1, 1 and 2 keV above the threshold energy for the 3d→5f excitations (ET ∼ 3.3 keV). The cross section measurements were made possible by using the GSFC x-ray microcalorimeter at the Livermore EBIT facility. The absolute cross sections are determined from the ratio of the intensity of the collisionally excited bound-bound transitions to the intensity of the radiative recombination lines produced in EBIT-I plasmas. The effects of polarization and Auger decay channels are accounted for in the cross section determination. Measured cross sections are compared with those from HULLAC, DWS and FAC calculations. The measurem...

Charge exchange recombination, the transfer of one or more electrons from an atomic or molecular system to a positive ion, is a common phenomenon affecting laboratory and astrophysical plasmas. Controlled studies of this process in electron beam ion traps during the past one and a half decades have produced multiple observations that are difficult to explain with available spectral models. Some of the most recent observations are so puzzling that they bring in doubt the existence of a coherent predictive capability for line formation by charge exchange, making investigations of charge exchange a fertile ground for continued measurements and theoretical development.

We review our recent high resolution experiments on photoabsorption by Fe14+ [M. C. Simon, et al., Phys. Rev. Lett. 105, 183001 (2010)], Fe15+, and Ar12+ [M. C. Simon, et al., J. Phys. B-At. Mol. Opt. Phys. 43, 065003 (2010)] at photon energies up to 1 keV. These ions play an essential role in photoionized astrophysical plasmas. Diagnostics of X-ray binary systems rely heavily on precise identification and knowledge of absorption lines. Novel experiments using an electron beam ion trap, FLASH EBIT, in combination with monochromatic synchrotron radiation allow us to investigate ions in charge states hitherto out of reach. Trapped ions can be prepared in any charge state at target densities sufficient to measure absorption cross sections below 0.1 Mb. This results in benchmark state-of-the-art predictions of the transitions wavelengths, widths, and absolute cross sections.

The XRS microcalorimeter will be launched in 2005 as part of the Astro‐E2 mission. It will cover the energy band from 0.3 to 10 keV with a nearly constant energy resolution of 6.0 eV and a peak effective area of 200 cm2 at 1.5 keV. The XRS will provide unprecedented throughput and resolving power, particularly at high energies. Detailed spectral features in the Fe K region will be resolved for the first time, providing access to spectroscopic diagnostics for a wide range of astrophysical objects. In this presentation we will describe the XRS instrument, details of its spectral performance, and how it compares to the current high‐resolution instruments on the Chandra and XMM‐Newton observatories.

Celestial objects are often home to complex, dynamic, intriguing environments. High‐resolution x‐ray spectra from these sources measured by satellites such as the Chandra, XMM‐Newton, the Solar Maximum Mission, and the soon‐to‐be‐launched Astro‐E2 provide a means for understanding the physics governing these sources. Especially rich is the x‐ray emission from L‐shell transitions in highly charged iron ions. This emission is the source of a variety of diagnostics whose utility lies in the accuracy of the atomic data employed to model the x‐ray spectra. The atomic data used to describe these diagnostics are generally provided by large theoretical calculations and benchmarked by laboratory data. In this paper we discuss laboratory measurements of Fe L‐shell x‐ray emission including wavelengths, relative and absolute excitation cross sections, and line ratios that provide diagnostics of temperature and density.

Recent measurements of the K‐shell and L‐shell x‐ray spectra of highly charged helium‐like and neonlike ions are presented that were performed on the Livermore electron beam ion traps and the Princeton tokamaks. These measurements provide new insights into collisional and indirect line formation processes, identifications of forbidden lines, and a new plasma line diagnostic of magnetic field strength.

In the past year a spare NASA/GSFC Astro-E microcalorimeter has been installed, tested, and run successfully on the electron beam ions traps EBIT-I and EBIT-II at the Lawrence Livermore National Laboratory. The microcalorimeter complements crystal and grating spectrometers already part of the LLNL ebit program making it possible to measure a broad bandwidth (∼0.3–10 keV) with moderate resolution while simultaneously measuring a narrow bandwidth (∼0.7–1.3 keV) with high resolution. An overview of recent work is presented including measurements by the microcalorimeter of absolute excitation cross sections. These results continue our effort to provide atomic data of high quality to be used as benchmarks for theoretical calculations and to be included in atomic data bases employed by spectral fitting packages used to interpret spectra obtained by XMM-Newton and the Chandra X-Ray Observatory.

Charge transfer reactions involving highly charged ions up to U91+ are being studied using x-ray spectroscopic techniques. The measurements are performed using ions produced in situ in a cylindrical trap with very low kinetic energy (⩽3 eV/amu). The observed K-shell and L-shell x-ray emission show prominent features from high-n levels decaying to the ground level. Such emission can serve as a diagnostic marker for charge transfer processes in plasmas, for example in cometary comae or in ion traps. The emission is enabled by electron capture into states with low orbital angular momentum, mainly l=1. The observed spectra, thus, provide a handle on determining the fraction of electron capture into low-l states that can be used for testing theoretical models in the limit of low collision energy. The present paper summarizes the progress made to date.

With the implementation of a transmission-type curved crystal spectrometer at the Livermore high-energy electron beam ion trap (SuperEBIT) the window on sub-eV level measurements of the ground-state quantum electrodynamics and the two-electron quantum electrodynamics of high-Z ions has been opened. High-resolution spectroscopic measurements of the Kα spectra of hydrogenlike Xe53+ and heliumlike Xe52+ are presented. The electron-impact excitation cross sections have been determined relative to the radiative recombination cross sections. The electron-impact energy was 112 keV which is about 3.7 times the excitation threshold for the n=2→1 transitions. Although the relative uncertainties of the measured electron-impact excitation cross sections range from about 20% to 50%, significant disagreement between the measured and calculated cross section values has been found for one of the helium-like xenon lines. Overall, the comparison between experiment and theory shows that already for xenon (Z=54) the Breit in...

One of the dominant forms of astronomical line emission in the 6 A to 18 A spectral region is line emission produced by n=n′ to n=2 transitions in Fe16+ to Fe23+ (i.e., Fe L‐shell n‐2 line emission). Using the Lawrence Livermore National Laboratory electron beam ion trap (EBIT) facility, we have carried out a number of measurements designed to address astrophysical issues concerning Fe L‐shell line emission. Desired ions are produced and trapped using the nearly monoenergetic electron beam of EBIT Trapped ions are collisionally excited and the resulting X‐ray line emission detected using Bragg crystal spectrometers. We have recently completed a line survey of Fe L‐shell 3‐2 line emission. The line survey will allow a more reliable accounting of line blending in astronomical spectra. We have now begun a series of broadband, high resolution line ratio measurements. These measurements are designed to benchmark atomic calculations used in astronomical plasma emission codes and also for comparison with X‐ray spectral observations of astronomical objects. Initial measurements have been carried out in Fe23+. Preliminary results agree with distorted wave calculations to within 20 percent and better.