Livermore Electron Beam Ion Trap Research Articles

K-shell X-ray transition energies of multi-electron ions of silicon and sulfur

Prompted by the detection of K-shell absorption or emission features in the spectra of plasma surrounding high mass X-ray binaries and black holes, recent measurements using the Livermore electron beam ion trap have focused on the energies of the n=2 to n=1 K-shell transitions in the L-shell ions of lithiumlike through fluorinelike silicon and sulfur. In parallel, we have made calculations of these transitions using the Flexible Atomic Code and the multi-reference Møller-Plesset (MRMP) atomic physics code. Using this code we have attempted to produce sets of theoretical atomic data with spectroscopic accuracy for all the L-shell ions of silicon and sulfur. We present results of our calculations for oxygenlike and fluorinelike silicon and compare them to the recent electron beam ion trap measurements as well as previous calculations.

Lineshape spectroscopy with a very high resolution, very high signal-to-noise crystal spectrometer

We have developed a high-resolution x-ray spectrometer for measuring the shapes of spectral lines produced from laser-irradiated targets on the Orion laser facility. The instrument utilizes a spherically bent crystal geometry to spatially focus and spectrally analyze photons from foil or microdot targets. The high photon collection efficiency resulting from its imaging properties allows the instrument to be mounted outside the Orion chamber, where it is far less sensitive to particles, hard x-rays, or electromagnetic pulses than instruments housed close to the target chamber center in ten-inch manipulators. Moreover, Bragg angles above 50° are possible, which provide greatly improved spectral resolution compared to radially viewing, near grazing-incidence crystal spectrometers. These properties make the new instrument an ideal lineshape diagnostic for determining plasma temperature and density. We describe its calibration on the Livermore electron beam ion trap facility and present spectral data of the K-shell emission from highly charged sulfur produced by long-pulse as well as short-pulse beams on the Orion laser in the United Kingdom.

MEASUREMENT OF THE RADIATIVE DECAY RATE AND ENERGY OF THE METASTABLE LEVEL IN Fe xvii

ABSTRACT Measurements at the Livermore electron beam ion trap have been performed in order to infer the energy and the radiative lifetime of the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level in the Fe xvii spectrum. This is the longest-lived level in the neonlike iron ion, and its radiative decay produces the Fe xvii line at 1153 Å, feeding the population of the ( 1 s 2 2 s 2 2 p 3 / 2 5 3 s 1 / 2 ) J = 1 ?> upper level of one of the most prominent lines in the Fe xvii L-shell X-ray spectrum, commonly dubbed 3 G ?> . In the presence of a strong ( ≥ ?> few kG) magnetic field, the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level has a finite probability to decay directly to the ( 1 s 2 2 s 2 2 p 6 ) J = 0 ?> neonlike ground level via the emission of an L-shell X-ray. Our measurements allow us to observe this X-ray line in the Fe xvii L-shell spectrum and from it to infer the radiative rate for the magnetic dipole decay of the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level to the ( 1 s 2 2 s 2 2 p 3 / 2 5 3 s 1 / 2 ) J = 1 ?> . Our result of ( 1.45 ± 0.15 ) × 10 4 ?> s−1 is in agreement with predictions. We have also measured the wavelength of the associated X-ray line to be 16.804 ± 0.002 Å, which means that the line is displaced 1.20 ± 0.05 eV from the neighboring ( 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 1 → ( 2 s 2 2 p 6 ) J = 0 ?> transition, commonly labeled 3 F ?> . From our measurement, we infer 5950570 ± 710 cm−1 for the energy of the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level.

Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics

The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.

Influence of radiative cascades on the polarization and angular distribution of radiation following electron-impact excitation of He-like Fe24+ ions

Detailed calculations are carried out for the electron-impact excitation cross sections from the ground state 1s2(J = 0) to the individual magnetic sublevels of the excited state 1s2s1/2 (J = 1) of highly charged He-like Fe24+ ions using a fully relativistic distorted-wave method. The cascades contributions from high-lying levels 1s2p, 1snl (n = 3, 4, 5, 6; l = s, p, d) to the cross sections and the polarization properties of the 1s2s(J = 0) line are investigated systematically. It is found that the 1s2p, 1s3l, and 1s4l (l = s, p, d) excited states have significant effects and make the cross sections increase evidently. These dramatic influences also lead to a remarkable decrease in the linear polarization and angular distribution of subsequent x-ray radiation. The present results are in good agreement with the previous theoretical results and the polarization measurements performed at the Livermore electron beam ion trap.

Dielectronic satellite lines of Fe XVII

We have been measuring the L-shell x-ray emission produced by dielectronic recombination of neonlike Fe16+ ions populating doubly excitated levels of the form 1s22l73ℓn'ℓ' in Fe15+. The measurements are carried out at the Livermore electron beam ion trap facility, where we isolate dielectronic resonances by choice of the electron beam energy. We utilize crystal spectrometers to record the x-ray lines generated in the radiative deexcitation of the 1s22l73ℓn'ℓ' upper levels. The measurements aim to support the identification of such lines in low-density astrophysical plasmas.

High-resolution grazing-incidence grating spectrometer for temperature measurements of low-Z ions emitting in the 100-300 Å spectral band.

We have constructed a high-resolution grazing-incidence spectrometer designed for measuring the ion temperature of low-Z elements, such as Li(+) or Li(2 +), which radiate near 199 Å and 135 Å, respectively. Based on measurements at the Livermore Electron Beam Ion Trap we have shown that the instrumental resolution is better than 48 mÅ at the 200 Å setting and better than 40 mÅ for the 135-Å range. Such a high spectral resolution corresponds to an instrumental limit for line-width based temperature measurements of about 45 eV for the 199 Å Li(+) and 65 eV for the 135 Å Li(2 +) lines. Recently obtained survey spectra from the Lithium Tokamak Experiment at the Princeton Plasma Physics Laboratory show the presence of these lithium emission lines and the expected core ion temperature of approximately 70 eV is sufficiently high to demonstrate the feasibility of utilizing our high-resolution spectrometer as an ion-temperature diagnostic.

Atomic physics and ionization balance of high-Z Ions: Critical ingredients for characterizing and understanding high-temperature plasmas

A correct description of the ionization balance of high-Z ions, i.e., the fractional abundance of different charge states of a particular element, is critical for interpreting diagnostic line ratios, for describing radiation flow within and out of the plasma, and for assessing the energy balance of high-temperature plasmas. Despite the fundamental nature of this atomic physics parameter, the ionization balance as a function of plasma electron density and electron temperature is generally rather poorly known both experimentally and theoretically. This is the case irregardless of the type of plasma, i.e., low-density astrophysical and coronal plasmas, intermediate density magnetically confined fusion plasmas, or high energy density (HED) laboratory plasmas. We illustrate these points by reviewing existing measurements of the ionization balance of high-Z elements in high-temperature plasmas and discussing the difficulties associated with ionization balance calculations. We focus on the two high-Z elements tungsten (Z=74) and gold (Z=79), which play important roles in magnetic fusion and HED plasmas and for which we present calculations of the ionization energies for each charge state. We show that the accuracy of the treatment of dielectronic recombination is currently a limiting factor in proper modeling of the ionization balance and propose “differential” measurements that determine the amount of dielectronic recombination concurrently with the ionization balance as the next step for advancing ionization balance modeling. As an example of the differential measurement approach, we present recent experiments carried out at the Livermore electron beam ion trap, which investigated the ionization balance of gold in the presence of beam-resonant dielectronic recombination. These plasmas limit the immense complexity of dielectronic recombination resonances so that both approximate and reasonably complete detailed calculations can be compared to the measurements. This represents a path forward for constructing and selecting those approximations that produce the most reliable ionization balance models.

Measuring plasma impurities in Alcator C-Mod as a function of time in the extreme ultraviolet1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

A flat-field grazing-incidence grating spectrometer has been installed on the MIT Alcator C-MOD tokamak, following the installation of such a spectrometer on the Livermore electron beam ion trap facility and on the National Spherical Torus Experiment at Princeton. The spectrometer employs a variable space grating with an average spacing of 2400 lines/mm and covers the 10–70 Å wavelength band. It is being used to monitor the presence of impurity ions such as boron, oxygen, fluorine, argon, calcium, iron, molybdenum, and tungsten, and to calibrate spectral diagnostics of astrophysical plasmas. The Alcator instrument provides spectral emission data in a density regime that is one to three orders of magnitude higher than that covered by the other two instruments and thus produces complementary data.

Tungsten spectroscopy at the Livermore electron beam ion trap facility1This review is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

The utilization of tungsten spectroscopy for diagnostics of magnetically confined fusion plasmas requires the radiative properties of tungsten ions to be accurately known. At the Lawrence Livermore National Laboratory, a program to gather spectroscopic data on tungsten ions has been initiated with the purpose to study spectral signatures and identify candidate fusion plasma diagnostics. In this paper, an overview of recent results from the Livermore WOLFRAM spectroscopy project is presented, which includes experimental investigations at the EBIT-I and SuperEBIT electron beam ion traps. In particular, the spectra of highly charged M- and L-shell tungsten ions have been studied. These investigations cover energy measurements of n = 2 to n = 2, 3 transitions in Ne-like W64+ through Li-like W71+ ions and soft X-ray measurements of n = 3 to n = 3, 4 transitions in M-shell ions with emphasis on the Ni-like W46+ and Si-like W60+ through Na-like W63+ ions. The measurements are complemented by atomic-structure calculations and spectral modeling using the Flexible Atomic Code (FAC).

Spectroscopy of M-shell x-ray transitions in Zn-like through Co-like W

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.

Laboratory Measurements of 3 → 2 X‐Ray Line Ratios of F‐like Fexviiiand Nixx

The intensity ratios of 3 {yields} 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 {yields} 2p/3d {yields} 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.

Cascade effects on the polarization of He-like Fe1s2l−1s2x-ray line emission

We calculate x-ray line polarization degrees for cases with axial symmetry using a collisional-radiative magnetic-sublevel atomic kinetics model and the properties of multipole radiation fields. This approach is well suited for problems where the alignment is determined by the competition between many atomic processes. We benchmark this method against polarization measurements performed at the Livermore electron beam ion trap, and we study the 3-to-2 cascade effects on the polarization of 2-to-1 lines in He-like Fe.

Measurement of electron impact collisional excitation cross sections of Ni to Ga-Like Gold

We are measuring the cross sections for the 3d→4f and 3d→5f excitations in Ni- to Ga-like Au in beam plasmas created in the Livermore electron beam ion trap EBIT-I. The measurements are possible by using the high-resolution broadband coverage of the Goddard Space Flight Center micro-calorimeter. The cross sections are determined from the ratio of the intensity of the collisionally excited lines to the intensity of the radiative recombination lines. The value of the excitation cross section of the 3d3/2→5f5/2 transition in Au50+ (Cu-like) is presented and compared to distorted wave calculations.

New Results in Laboratory X-ray Astrophysics

AbstractA multi-faceted, multi-institutional laboratory astrophysics program is carried out at the Livermore electron beam ion trap facility, which is a mature spectroscopic source with unsurpassed controls and capabilities, and an unparalleled assortment of spectroscopic equipment, including a full complement of grating and crystal spectrometers and a 6x6 micro-calorimeter array. Recent results range from the calibration of x-ray diagnostics, including the Fe XVII and Fe XXV emission lines, extensive lists of L-shell ions, the first laboratory simulation and fit of a cometary x-ray emission spectrum, and the discovery of new spectral diagnostics for measuring magnetic field strengths.

Testing LaMgAl11O19 crystal for x-ray spectroscopy

We investigated the properties of the rare earth crystal LaMgAl11O19 and its application to soft x-ray spectroscopy. Its relative reflectivity and half-width rocking curve were measured to up to the reflection order of 28. In addition, a comparative measurement of the iron L-shell soft x-ray line emission was made on the EBIT-I Livermore electron beam ion trap by fielding the LaMgAl11O19 crystal side by side with a rubidium hydrogen phthalate crystal in a flat crystal spectrometer. From these measurements, reflectivity and spectral resolving power were determined.

Laboratory Measurements of 3 → 2 X-Ray Emission Lines of Ne-like Ni xix

The intensity ratios between 3 → 2 emission lines in Ni XIX were measured on the Livermore electron beam ion trap (EBIT-I) with a flat-field grating spectrometer and the NASA/Goddard Space Flight Center X-ray microcalo-rimeter. The results are consistent with earlier measurements of Fe XVII and other Ne-like ions at Livermore and confirm the problems in the atomic modeling of the direct collisional excitation for Ne-like systems.

Metastatic breast cancer (19 years later) mimicking obstructing primary colon cancer

A correct description of the ionization balance of high-Z ions, i.e., the fractional abundance of different charge states of a particular element, is critical for interpreting diagnostic line ratios, for describing radiation flow within and out of the plasma, and for assessing the energy balance of high-temperature plasmas. Despite the fundamental nature of this atomic physics parameter, the ionization balance as a function of plasma electron density and electron temperature is generally rather poorly known both experimentally and theoretically. This is the case irregardless of the type of plasma, i.e., low-density astrophysical and coronal plasmas, intermediate density magnetically confined fusion plasmas, or high energy density (HED) laboratory plasmas. We illustrate these points by reviewing existing measurements of the ionization balance of high-Z elements in high-temperature plasmas and discussing the difficulties associated with ionization balance calculations. We focus on the two high-Z elements tungsten (Z = 74) and gold (Z = 79), which play important roles in magnetic fusion and HED plasmas and for which we present calculations of the ionization energies for each charge state. We show that the accuracy of the treatment of dielectronic recombination is currently a limiting factor in proper modeling of the ionization balance and propose “differential” measurements that determine the amount of dielectronic recombination concurrently with the ionization balance as the next step for advancing ionization balance modeling. As an example of the differential measurement approach, we present recent experiments carried out at the Livermore electron beam ion trap, which investigated the ionization balance of gold in the presence of beam-resonant dielectronic recombination. These plasmas limit the immense complexity of dielectronic recombination resonances so that both approximate and reasonably complete detailed calculations can be compared to the measurements. This represents a path forward for constructing and selecting those approximations that produce the most reliable ionization balance models.

Determination of the charge state distribution of a highly ionized coronal Au plasma.

We present the first definitive measurement of the charge state distribution of a highly ionized gold plasma in coronal equilibrium. The experiment utilized the Livermore electron beam ion trap EBIT-II in a novel configuration to create a plasma with a Maxwellian temperature of 2.5 keV. The charge balance in the plasma was inferred from spectral line emission measurements which accounted for charge exchange effects. The measured average ionization state was 46.8+/-0.75. This differs from the predictions of two modeling codes by up to four charge states.

Experimental Transition Rate of the Green Coronal Line of Fexiv

The transition probability of the electric dipole forbidden transition in the ground state of Fe XIV (Al-like), the green coronal line at 5302.86 A, has been measured using the Livermore electron beam ion trap. Our result for the 3s23p2 2P atomic level lifetime is 16.74 ± 0.12 ms, which differs significantly from an earlier measurement, and is the most accurate one to date. The measured transition rate of 59.7 ± 0.4 s-1 corroborates some earlier calculations, but not all of the more recent ones.