K. J. Reed

Diagnostic Utility of the Relative Intensity of 3C to 3D in Fe XVII

The relative intensity R of the resonance and intercombination line in neon-like Fe XVII, located at 15.01 and 15.26 A, respectively, has been measured at the Lawrence Livermore National Laboratory electron beam ion trap EBIT-II as a function of the relative abundance of sodium-like Fe XVI. Our measurements identify several Fe XVI lines and one Fe XV line in this region. We show that an Fe XVI inner shell satellite line coincides with the intercombination line and can significantly reduce the apparent R. We measure R = 1.90 ± 0.11 when the relative abundance of Fe XVI to Fe XVII is ~1. This explains the anomalously low ratios observed in the solar and stellar coronae. The fact that the apparent relative intensity of the resonance and intercombination line in Fe XVII is sensitive to the strength of an Fe XVI inner shell satellite, and therefore, the relative abundance of Fe XVI to Fe XVII, makes the line ratio a diagnostic of temperature.

Laboratory Measurements of Iron L-Shell Emission: 3→2 Transitions of Fe XXI-XXIV between 10.5 and 12.5 Å

Using the electron beam ion trap EBIT-II facility at Lawrence Livermore National Laboratory, we have measured the iron L-shell spectrum between 10.5 and 12.5 A for Fe XXI-XXIV with a spectral resolution of ~30 mA. The relative line intensities of strong 3 → 2 transitions for each charge state are measured as functions of electron energy and compared to distorted wave (DW) calculations. The contributions of resonant processes, namely, resonant excitation (RE) and spectroscopically unresolved dielectronic recombination (DR) satellites, are investigated. The RE contributions are shown to be less than the experimental and theoretical uncertainties for plasma in collisional ionization equilibrium. The unresolved DR satellites, however, enhance the emissivities of almost all lines, some by as large as 15%, consistent with our earlier measurements for Fe XXIV. The DW results agree with our measurements to better than 20% under the condition of collisional ionization equilibrium. The line emissivities in the widely used spectral synthesis model, MEKAL, are also compared to our measurements and are found to be discrepant at a greater than 20% level for some lines.

Laboratory Measurements of Fe XXIV L-Shell Line Emission

Recent ASCA spectra exhibit discrepancies with the relative line intensities of various Fe XXIII and XXIV L-shell emission lines predicted by standard plasma emission codes. To address this issue, we have carried out a series of high-resolution, broadband measurements of Fe XXIV line emission using an electron beam ion trap facility. X-ray lines produced in the trap are detected and resolved using Bragg crystal spectrometers. We report measurements of 3 → 2 and 4 → 2 transitions, which result primarily from electron impact excitation. Overall, good agreement is found with distorted wave calculations.

Laboratory astrophysics: Measurements of n=n′ to n=2 line emission in Fe16+ to Fe23+

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 s...

Polarization measurements of the Lyman-{alpha}{sub 1} x-ray emission lines of hydrogenlike Ar{sup 17+} and Fe{sup 25+} at high electron-impact energies

We have measured the polarization of the 2p{sub 3/2}{yields}1s{sub 1/2} Lyman-{alpha}{sub 1} x-ray line of hydrogenlike Ar{sup 17+} and Fe{sup 25+} at electron-impact energies ranging from 7 to 25 threshold units. The highly charged argon and iron ions were produced using the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. A combination of two crystal spectrometers and a microcalorimeter were used to record the Lyman-{alpha} x-ray emission of Ar{sup 17+} and Fe{sup 25+} and to infer the polarization of the Lyman-{alpha}{sub 1} line. Our results show a systematic discrepancy with the predictions of distorted-wave calculations.

New Insights into the X‐ray Spectra of Heliumlike and Neonlike Ions

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.