National Laboratory Electron Beam Ion Research Articles

Mitigation of Finite Bandwidth Effects in Time-Division-Multiplexed SQUID Readout of TES Arrays

Time division multiplexing (TDM) is being developed as the readout technology of the X-ray integral field unit (X-IFU), a 3,168-pixel X-ray transition-edge sensor (TES) imaging spectrometer that is part of the European Space Agency's Athena satellite mission. Recent improvements in the low X-ray event count rate performance of TDM have been driven by increases in multiplexer bandwidth and the mitigation of settling transients. These methods and design changes have improved the 32-row multiplexed resolution of a NASA LPA 2.5a array from an initial (2.73 ± 0.03) eV to (1.97 ± 0.01) eV resolution at 5.9 keV. We discuss these recent advances in TDM readout, which have been implemented in an 8-column × 32-row spectrometer that will be deployed at the Lawrence Livermore National Laboratory electron beam ion trap (EBIT) facility, and present a model that will inform the design of future systems.

Low charge states of Si and S in Cygnus X-1

Strong, relatively short, absorption dips have been observed in the x-ray light curves measured from the high mass x-ray binary system Cygnus X-1. With increasing strength of the dips, which are believed to be caused by ‘clumps’ of cold material present in the stellar wind of Cyg X-1's companion star, K-shell absorption lines in L-shell ions of Si and S develop. To determine the bulk motion of the clumps via the Doppler shifts of these lines with high accuracy, we measured their reference energies using the Lawrence Livermore National Laboratory electron beam ion trap EBIT-I and EBIT Calorimeter Spectrometer. Our findings—shifts consistent with zero velocity of the absorber throughout all ionization states at orbital phase zero—provide evidence for an onion-like ion structure of the clumps.

Calibration of a high resolution grating soft x-ray spectrometer

The calibration of the soft x-ray spectral response of a large radius of curvature, high resolution grating spectrometer (HRGS) with a back-illuminated charge-coupled device detector is reported. The instrument is cross-calibrated for the 10-50 Å waveband at the Lawrence Livermore National Laboratory electron beam ion trap (EBIT) x-ray source with the EBIT calorimeter spectrometer. The HRGS instrument is designed for laser-produced plasma experiments and is important for making high dynamic range measurements of line intensities, line shapes, and x-ray sources.

Laboratory simulation of cometary X-rays using a high-resolution microcalorimeter

X-ray emission following charge exchange has been studied at the University of California Lawrence Livermore National Laboratory electron beam ion traps EBIT-I and EBIT-II using a high-resolution microcalorimeter. The measured spectra include the K-shell emission from hydrogenlike and heliumlike C, N, O, and Ne needed for simulations of cometary x-ray emission. A comparison of the spectra produced in the interaction of O8+ with N2 and CH4 is presented that illustrates the dependence of the observed spectrum on the interaction gas.

The study of X-ray M-shell spectra of W ions from the Lawrence Livermore National Laboratory Electron Beam Ion Trap

M-shell spectra of W ions have been produced at the Lawrence Livermore National Laboratory EBIT-II electron beam ion trap-II at different energies of the electron beam. A survey has been performed at 2.4, 2.8, and 3.6 keV, and for steps in energy of 100 eV over the 3.9–4.6 keV energy range. The analysis of 11 W spectra has shown the presence of a wide variety of ionization stages from Se-like to Cr-like W; the appearances of these ionization stages correlate well with the energy of their production. The present paper focuses on the identification of 63 experimental features of W ions in a spectral region from 5 to 6 Å (1 Å = 10–10 m) using calculations with inclusion of all ionization stages matching this spectral region. The majority of lines in all spectra have been identified and assigned to the 4f → 3d and 4d → 3p transitions. This is the first work that lists a comprehensive identification of so many resolved spectral features of X-ray M-shell transitions in W ions recorded in such detail in the laboratory. PACS Nos.: 52.58.Lq,32.30.Rj,52.70.La

Extraction of highly charged Au ions from a multiampere electron beam EBIS at BNL

Excellent progress has been made in the operation of the Brookhaven National Laboratory electron beam ion source (EBIS), which is a prototype for an EBIS that could meet requirements for a RHIC preinjector. We have achieved very stable operation of the electron beam at 10 A through the EBIS trap. Ion injection of low charge gold ions from a low energy vacuum ion source [Brown et al., Rev. Sci. Instrum. 65, 1260 (1994)] and subsequent extraction of these ions with most probable charge state Au34+ has been demonstrated with electron beams up to 8 A. The total ion charge for gold measured on current transformer at the EBIS exit was 55 nC after a 30 ms confinement period. This corresponds to ∼85% of the theoretical ion trap capacity and exceeds our goal of 50% neutralization. The collected ion charge is proportional to the electron current and the gold charge state scales with the electron current density. Details of the EBIS configuration, total charge measurements, and time-of-flight spectra are given.

Diagnostic Utility of the Relative Intensity of 3C to 3D in F[CLC]e[/CLC] [CSC]xvii[/CSC

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.

Thin-window high-efficiency position sensitive proportional counter for the vacuum flat crystal spectrometers on the Lawrence Livermore National Laboratory electron beam ion trap (abstract)

We have mounted 1 μm thick aluminized polyimide windows onto the position sensitive proportional counters employed by the wide-band flat crystal spectrometers at the Lawrence Livermore National Laboratory electron beam ion trap experiment. The aluminized polyimide, supported by thin wires across the short axis of the window, is used to isolate the detection chamber of the proportional counters, which operate at a pressure of 760 Torr, from the vacuum chamber of the spectrometer. The windows are modified versions of those developed for the proportional counters which were used during ground calibration of the Chandra X-ray Observatory. The transmission properties of these windows are, therefore, well known. The increased transmission efficiency of the polyimide windows relative to the 4 μm thick polypropylene window material previously employed by our proportional counters has extended the useful range of the spectrometer from roughly 20 to 30 Å at energies below the carbon edge, as well as increasing detection efficiency at wavelengths beyond the carbon edge. Using an octadecyl hydrogen maleate crystal with 2d=63.5 Å, we demonstrate the increased wavelength coverage by measuring the resonance, intercombination, and forbidden lines in helium-like N VII in two different density regimes. The thin polyimide windows have also increased the efficiency of the spectrometers entire wavelength range. To demonstrate the increased efficiency we compare the Fe XVII spectrum in the 15–17 Å band measured with the 1 μm aluminized polyimide windows to the 4 μm aluminized polypropylene windows. The comparison shows an average increase in efficiency of ∼40%. The polyimide windows have a significantly lower leak rate than the polypropylene windows making it possible to achieve approximately an order of magnitude lower pressure in the spectrometer vacuum chamber which reduces the gas load on the trap region.

Electron capture fromH2to highly charged Th and Xe ions trapped at center-of-mass energies near 6 eV

Ions with charge states as high as $80+,$ produced in the Lawrence Livermore National Laboratory electron beam ion trap were extracted and transferred to a Penning ion trap (RETRAP). RETRAP was operated at cryogenic temperature in the field of a superconducting magnet. The stored low-energy ions collided occasionally with ${\mathrm{H}}_{2}$ molecules in the ultrahigh-vacuum environment of the trap, capturing one or two electrons and reducing the charge state of the ions. The number of ions was monitored nondestructively by ramping the axial oscillation frequencies of the ions through resonance with a tuned circuit composed in part of trap capacitance and an external inductor. This produced resonance signals whose square is proportional to the number of ions in each charge state. These signals were recorded vs storage time to determine the electron-capture rates. From these rates the relative electron-capture cross sections were obtained using estimates of the mean ion energies based on modeling the ion storage, and with the aid of a density calibration measurement using ${\mathrm{Ar}}^{11+}.$ The measured total electron-capture cross sections are consistent with a linear increase with charge state $q.$ The cross-section data for the highest charge states lie above the predictions of the absorbing sphere model, but agree within uncertainties in both experiment and theory. The true double-capture cross-section fraction for $q>35$ is near 25%. The results are discussed with relation to measurements on lower charge states, and with theory.

Polarization-dependent spectra of x-ray dielectronic satellite lines of Be-like Fe

We have studied the polarization properties of dielectronic satellite lines in Be-like Fe ions excited through resonant electron capture by an electron beam. Using the photon density-matrix formalism, we have calculated the degree of polarization and polarization-dependent spectra of dielectronic satellite lines, i.e., the spectral intensity distribution of lines associated with a given polarization state. Theoretical results have been compared with experiments performed at the Lawrence Livermore National Laboratory electron-beam ion trap where dielectronic satellite line emission from Fe ions produced at different energies of the electron beam was simultaneously recorded with two crystal spectrometers. These spectrometers had different polarization sensitivities. The experimental spectra recorded by the two spectrometers are reproduced by the theory. This ability to model the polarization dependence of x-ray line spectra is important for the diagnosis of electron beams in plasmas.

New experimental initiatives using very highly charged ions from an “electron beam ion trap”

A short review of the experimental program in highly-charged heavy ion physics conducted at the Lawrence Livermore National Laboratory Electron Beam Ion Trap (EBIT) facility is presented. The heavy-ion research, involving ions up to fully stripped U92+, includes precision x-ray spectroscopy and lifetime studies, electron impact ionization and excitation cross section measurements. The investigations of ion-surface interactions following the impact of high-Z highly charged ions on surfaces are aimed to study the neutralization dynamics effecting the ion and the response of the surface as well. The combination of an EBIT% with a cryogenic Penning Trap (“RETRSP”) allows to conduct experiments with ultra cold (e.g. 10 K) very highly charged ions. These studies of charge exchange processes, Coulomb crystals and measurements of hyperfine transitions using laser spectroscopy are in progress.

Electron emission and image-charge acceleration for the impact of very highly charged ions on clean gold.

We present total yields for emission of slow (${\mathit{E}}_{\mathit{e}}$\ensuremath{\le}50 eV) electrons due to the impact of slow (${\mathit{v}}_{\mathit{p}}$\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ m/s) highly charged ions [${\mathrm{Ar}}^{\mathit{q}+}$ (q\ensuremath{\le}18), ${\mathrm{Xe}}^{\mathit{q}+}$ (q\ensuremath{\le}51), and ${\mathrm{Th}}^{\mathit{q}+}$ (q\ensuremath{\le}80)] on clean polycrystalline gold. The highly charged ions were produced in the Lawrence Livermore National Laboratory electron-beam ion trap; electron yields have been derived from the respective measured electron emission statistics. The experimental data support a currently accepted scenario for multicharged ion-induced electron emission, which is largely based on a classical over-barrier model. In particular, we are able to distinguish different processes contributing to the total above-surface electron emission. In addition, an ultimate low-impact-energy limit due to projectile self-acceleration toward the metal surface, as a result of the projectile image charge, has been demonstrated and evaluated.

Precision measurement of the K alpha transitions in heliumlike Ge30+

A measurement of the 1{ital s}2{ital p} {sup 1}{ital P}{sub 1}{r arrow}1{ital s}{sup 2} {ital S}{sub 0} resonance transition in heliumlike germanium (Ge{sup 30+}) has been made on the Lawrence Livermore National Laboratory electron-beam ion trap to a precision of 21 ppm. The result is compared with theoretical values and confirms a trend previously seen in the differences between experiment and theory for this transition as a function of {ital Z}. Results for the 1{ital s}2{ital p} {sup 3}{ital P}{sub 1}{r arrow}1{ital s}{sup 2} {ital S}{sub 0} and 1{ital s}2{ital p} {sup 3}{ital P}{sub 2}{r arrow}1{ital s}{sup 2} {ital S}{sub 0} intercombination lines and for the 1{ital s}2{ital s} {sup 3}{ital S}{sub 1}{r arrow}1{ital s}{sup 2} {sup 1}{ital S}{sub 0} forbidden line are also presented and show similar differences with theoretical predictions.