D. Thorn

Laboratory Wavelengths of K-Shell Resonance Lines of O V and O VI

We present wavelength measurements of K-shell resonance lines of O V and O VI using the University of California Lawrence Livermore National Laboratory EBIT-I electron beam ion trap. The wavelength accuracy of better than 140 parts per million is sufficient to determine gas outflow velocities of warm absorbers associated with active galactic nuclei to within 40 km s-1 and better. Our measurements confirm that the outflow velocities associated with NGC 5548 and derived from the O V and O VI lines are similar to those derived from the O VII lines. These kinematic measurements make for further evidence that the X-ray and UV absorbers in these systems are truly two manifestations of the same physical outflow.

Laboratory Measurement and Theoretical Modeling of K-shell X-ray Lines from Inner-shell Excited and Ionized Ions of Oxygen

We present high resolution laboratory spectra of K-shell X-ray lines from inner-shell excited and ionized ions of oxygen, obtained with a reflection grating spectrometer on the electron beam ion trap (EBIT-I) at the Lawrence Livermore National Laboratory. Only with a multi-ion model including all major atomic collisional and radiative processes, are we able to identify the observed K-shell transitions of oxygen ions from O III to O VI. The wavelengths and associated errors for some of the strongest transitions are given, taking into account both the experimental and modeling uncertainties. The present data should be useful in identifying the absorption features present in astrophysical sources, such as active galactic nuclei and X-ray binaries. They are also useful in providing benchmarks for the testing of theoretical atomic structure calculations.

Performance of the EBIT calorimeter spectrometer.

The EBIT calorimeter spectrometer (ECS) is a new high-resolution, broadband x-ray spectrometer that has recently been installed at the Electron Beam Ion Trap Facility (EBIT) at the Lawrence Livermore National Laboratory. The ECS is an entirely new production class spectrometer that replaces the XRS/EBIT spectrometer that has been operating at EBIT since 2000. The ECS utilizes a 32-pixel x-ray calorimeter array from the XRS instrument on the Suzaku x-ray observatory. Eighteen of the pixels are optimized for the 0.1-10 keV band and yield 4.5 eV full width at half maximum energy resolution and 95% quantum efficiency at 6 keV. In addition, the ECS includes 14 detector pixels that are optimized for the high-energy band with a bandpass from 0.5 to over 100 keV with 34 eV resolution and 32% quantum efficiency at 60 keV. The ECS detector array is operated at 50 mK using a five stage cryogenic system that is entirely automated. The instrument takes data continuously for over 65 h with a 2.5 h recycle time. The ECS is a nondispersive, broadband, highly efficient spectrometer that is one of the prime instruments at the EBIT facility. The instrument is used for studies of absolute cross sections, charge exchange recombination, and x-ray emission from nonequilibrium plasmas, among other measurements in our laboratory astrophysics program.

Wavelength Measurements of Ni L-Shell Lines between 9 and 15 Å

We present accurate wavelength measurements of nickel L-shell X-ray lines resulting from Δn ≥ 1 transitions between 9 and 15 A. We have used the electron beam ion trap, SuperEBIT, at the Lawrence Livermore National Laboratory and a flat-field grating spectrometer to record the spectra. The most significant emission lines of Ni XIX-XXVI in our spectral coverage are identified, and their relative intensities are determined. The resulting data set provides valuable input for the analyses of high-resolution X-ray spectra of stellar coronae sources, including the Sun.

Overview of the Livermore electron beam ion trap project

The Livermore electron beam ion trap facility has recently been moved to a new location within LLNL, and new instrumentation was added, including a 32-pixel microcalorimeter. The move was accompanied by a shift of focus toward in situ measurements of highly charged ions, which continue with increased vigor. Overviews of the facility, which includes EBIT-I and SuperEBIT, and the research projects are given, including results from optical spectroscopy, QED, and X-ray line excitation measurements.

Rapid, Absolute Calibration of X-ray Filters Employed By Laser-Produced Plasma Diagnostics

The Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of x-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen x-ray energies. X rays are detected using the high resolution EBIT Calorimeter Spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the x-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification of filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1 to 15 keV. The EBIT calibration lab has been used to field diagnostics (e.g., the OZSPEC instrument) with fully calibrated x-ray filters at the OMEGA laser. Extensions to use the capability for calibrating filter transmission for the DANTE instrument on the National Ignition Facility are discussed.

Photometric calibration of an EUV flat field spectrometer at the advanced light source

The photometric calibration of an extreme ultraviolet flat field spectrometer has been done at the Advanced Light Source at Lawrence Berkeley National Laboratory. This spectrometer is used to record spectrum for atomic physics research from highly charged ions in plasmas created in the Livermore electron beam ion traps EBIT-I and SuperEBIT. Two calibrations were done each with a different gold-coated grating, a 1200 l/mm and a 2400 l/mm, that covered 75–300 A and 15–160 A, respectively. The detector for this calibration was a back thinned charge coupled device. The relative calibration was determined for several different incident angles for both gratings. Within the scatter of the data, the calibration was roughly insensitive to the incidence angle for the range of angles investigated.

Results from the National Spherical Torus Experiment x-ray crystal spectrometer

A high-resolution x-ray crystal spectrometer has recently been installed at the National Spherical Torus Experiment to record the satellite spectra of helium-like argon, Ar XVII, in the wavelength range from 3.94 to 4.00 A for measurements of ion and electron temperatures, and measurements of the ionization equilibrium of argon, which is of interest for studies of ion transport. The instrument presently consists of a spherically bent quartz crystal and a conventional one-dimensional position-sensitive multiwire proportional counter, but it will soon be upgraded to a new type of x-ray imaging crystal spectrometer by the installation of a large size (10 cm×30 cm) two-dimensional position-sensitive detector that will allow us to obtain temporally and spatially resolved spectra from a 80 cm high cross-section of the plasma. In its present configuration, the spectrometer has been optimized for high throughput so that it is possible to record spectra with small statistical errors with a time resolution of 10 ms...

Development of a high resolution x-ray spectrometer for the National Ignition Facility (NIF)

A high resolution (E/ΔE = 1200-1800) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in National Ignition Facility experiments. The instrument will be a diagnostic instrument manipulator positioned cassette designed mainly to infer electron density in compressed capsules from Stark broadening of the helium-β (1s2-1s3p) lines of krypton and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and focus (1) the Kr Heβ complex and (2) the Heα (1s2-1s2p) and Lyα (1s-2p) complexes onto a streak camera photocathode for time resolved measurement, and a third cylindrical or conical crystal will focus the full Heα to Heβ spectral range onto an image plate to provide a time integrated calibration spectrum. Calculations of source x-ray intensity, spectrometer throughput, and spectral resolution are presented. Details of the conical-crystal focusing properties as well as the status of the instrumental design are also presented.

Understanding reconstructed Dante spectra using high resolution spectroscopy

The Dante is an 18 channel filtered diode array used at the National Ignition Facility (NIF) to measure the spectrally and temporally resolved radiation flux between 50 eV and 20 keV from various targets. The absolute flux is determined from the radiometric calibration of the x-ray diodes, filters, and mirrors and a reconstruction algorithm applied to the recorded voltages from each channel. The reconstructed spectra are very low resolution with features consistent with the instrument response and are not necessarily consistent with the spectral emission features from the plasma. Errors may exist between the reconstructed spectra and the actual emission features due to assumptions in the algorithm. Recently, a high resolution convex crystal spectrometer, VIRGIL, has been installed at NIF with the same line of sight as the Dante. Spectra from L-shell Ag and Xe have been recorded by both VIRGIL and Dante. Comparisons of these two spectroscopic measurements yield insights into the accuracy of the Dante reconstructions.