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The M-intrashell spectra from Co-like Yb43+ through Na-like Yb59+ ions produced in an electron beam ion trap (EBIT) at the National Institute of Standards and Technology have been studied in the extreme ultraviolet (EUV) range. A few N-intrashell transitions for Co-like Yb43+ and Fe-like Yb44+ are also reported. The EUV radiation was observed with a flat-field grazing incidence spectrometer in the wavelength region of about 7.5 nm to 26.2 nm. The electron beam energies were varied between 3.6 keV and 18 keV to produce the ionization stages of interest. The line identifications were based on the large-scale simulations of the EBIT plasma emission using the non-Maxwellian collisional-radiative code NOMAD. A total of 76 previously unobserved spectral lines corresponding to electric-dipole and magnetic-dipole transitions in the above mentioned ions were identified and discussed. In particular, our accurate wavelength of 24.3855±0.0005 nm for a magnetic-dipole (M1) transition in the ground configuration of Co-like ion presents a solid benchmark for comparisons with the most advanced theories of atomic structure.

The electron-beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) was employed for the measurement and detailed analysis of the $\ensuremath{\delta}\ensuremath{\lambda}(^{124}\mathrm{Xe},^{136}\mathrm{Xe})$ isotopic shifts of the Al-like $3{s}^{2}3p\phantom{\rule{4pt}{0ex}}^{2}P_{1/2}\ensuremath{-}3{s}^{2}3p\phantom{\rule{4pt}{0ex}}^{2}P_{3/2}$, Al-like $3{s}^{2}3p\phantom{\rule{4pt}{0ex}}^{2}P_{1/2}\ensuremath{-}3{s}^{2}3d\phantom{\rule{4pt}{0ex}}^{2}D_{3/2}$, Mg-like $3{s}^{2}\phantom{\rule{4pt}{0ex}}^{1}S_{0}\ensuremath{-}3s3p\phantom{\rule{4pt}{0ex}}^{1}P_{1}$, Mg-like $3{s}^{2}\phantom{\rule{4pt}{0ex}}^{1}S_{0}\ensuremath{-}3s3p\phantom{\rule{4pt}{0ex}}^{3}P_{1}$, Na-like $3s\phantom{\rule{4pt}{0ex}}^{2}S_{1/2}\ensuremath{-}3p\phantom{\rule{4pt}{0ex}}^{2}P_{1/2}$ (${D}_{1}$), and Na-like $3s\phantom{\rule{4pt}{0ex}}^{2}S_{1/2}\ensuremath{-}3p\phantom{\rule{4pt}{0ex}}^{2}P_{3/2}$ (${D}_{2}$) transitions. Systematic analysis revealed possible line blends and contributing experimental uncertainties. Highly accurate atomic-structure calculations were conducted and used to determine the $\ensuremath{\delta}{\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}}^{136,124}$ difference in the mean-square nuclear charge radii of the two xenon isotopes. In the present work, $\ensuremath{\delta}{\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}}^{136,124}$ of 0.276 $\ifmmode\pm\else\textpm\fi{}$ 0.030 ${\mathrm{fm}}^{2}$ was obtained from the weighted average of the Na-like ${D}_{1}$, Mg-like $3{s}^{2}\ensuremath{-}3s3p$ and Al-like $3{s}^{2}3p\ensuremath{-}3{s}^{2}3p$ and $3{s}^{2}3p\ensuremath{-}3{s}^{2}3d$ transitions. This result confirms the value previously determined from the Na-like ${D}_{1}$ transition of 0.269 $\ifmmode\pm\else\textpm\fi{}$ 0.042 ${\mathrm{fm}}^{2}$. The uncertainty of our result is half of that of previous results for the same isotopes obtained from x-ray spectroscopy of muonic atoms, laser spectroscopy of neutral xenon atoms, and a global evaluation of charge radii. Our result is slightly outside the uncertainty of the value obtained from a King plot analysis of comparable precision. The present work illustrates that extreme-ultraviolet spectroscopy of highly charged ions is a viable approach for measurements of charge nuclear radii differences and can be used to benchmark conventional methods.

Extreme ultraviolet spectra of highly charged tungsten ions were produced with an electron beam ion trap at the National Institute of Standards and Technology and recorded with a flat-field grazing-incidence spectrometer. The spectra were measured in the wavelength range 2.7-17.3 nm while the beam energy varied between 1.65 and 2.00 keV. At these energies, the ionization stages from Zr-like W34+ to Se-like W40+ ions were observed. Large-scale collisional-radiative modelling was used to identify the strong lines, including 15 new ones, which represent electric dipole n = 4-4 transitions in these ions. While a good quantitative agreement between theoretical and experimental data was found for almost all ions, some of the tentatively identified wavelengths in W35+ significantly disagree from all available calculations.

The variation in mean-square nuclear charge radius of xenon isotopes was measured utilizing a new method based on extreme ultraviolet spectroscopy of highly charged Na-like ions. The isotope shift of the Na-like D1 (3s $^{2}$S$_{1/2}$ - 3p $^2$P$_{1/2}$) transition between the $^{124}$Xe and $^{136}$Xe isotopes was experimentally determined using the electron beam ion trap facility at the National Institute of Standards and Technology. The mass shift and the field shift coefficients were calculated with enhanced precision by relativistic many-body perturbation theory and multi-configuration Dirac-Hartree-Fock method. The mean-square nuclear charge radius difference was found to be $\delta^{136, 124}$ = 0.269(0.042) fm$^2$. Our result has smaller uncertainty than previous experimental results and agrees with the recommended value by Angeli and Marinova [I. Angeli and K. P. Marinova, At. Data and Nucl. Data Tables {\bf 99}, 69-95 (2013)]., Comment: 6 pages, 3 figures

Precise spectroscopic experiments with light atoms can provide information about nuclear properties that are very difficult to obtain in electron scattering experiments. For example, relative nuclear radii of low-Z isotopes can be determined accurately from isotope shifts. Theory has attained sufficient accuracy to study exotic, short-lived halo nuclei by interpreting precise spectroscopic measurements. However, serious inconsistencies remain in the measured isotope shifts for the D1 and D2 lines of the stable isotopes (6Li and 7Li). The latest experiments, within the last decade, are in strong disagreement with each other and with theory. We report on the progress of a new experiment at the National Institute of Standards and Technology (NIST) to measure these lithium D lines using an optical frequency comb. A preliminary result for the splitting isotope shift (SIS) is presented.

A new data acquisition system coupled to a backgammon-type gas proportional counter capable of single-photon counting over a wide range of count rates has been developed and replaces a CAMAC-based system. The new apparatus possesses improved architecture, interface technology, speed and diagnostic capability. System efficiency and throughput is significantly improved, especially in addressing earlier problems of hardware buffer downloads containing zero or repeat data and inefficient gating control. The new system is a PXI-based data acquisition apparatus including additional electronics, controlled by a graphical programming environment. It allows development of superior diagnostic tools for system optimisation and more stable performance. System efficiency is improved by 10% over a wide range of count rates (0.5 Hz–50 kHz). For the Backgammon Detector type, this represents a significant improvement in performance and applicability over previous systems. Characteristic and few-electron spectra collected on the new acquisition system are illustrated.

Careful measurements of highly charged ions (HCIs) colliding with gases and surfaces have provided glimpses of intense electronic interactions, but a comprehensive model for the interaction mechanisms, time scales, and resultant nano-features that bridges materials systems is yet to be realized. At the National Institute of Standards and Technology (NIST) electron beam ion trap (EBIT) facility, new apparatus is now connected to the HCI beamline to allow preparation of clean, atomically flat surfaces of single crystals, e.g. gold, tungsten and silicon, and deposition and patterning of thin films, e.g. high resistivity oxides, ferromagnetic metals, normal metals and superconductors. Experiments reported here focus on the electronic and morphological structure of HCI induced nano-features. Current activities are focused on using in situ scanning tunneling microscope (STM) on Au(1 1 1) and (separately) ex situ transport measurements to study electronic properties within HCI modified magnetic multilayer systems. Specifically, we are fabricating magnetic multilayers similar to magnetic tunnel junctions (MTJs) (important in advanced magnetic field sensors and superconducting Josephson junction devices) and using HCIs to adjust critical electronic properties. The electrical response of the tunnel junction to HCIs provides a novel approach to performing HCI-induced nanostructure ensemble measurements.

This paper mirrors and provides references to an invited review talk delivered by the first author at the 13th International Conference on the Physics of Highly Charged Ions. It briefly updates and extends an earlier review (J. D. Gillaspy, 2001 J. Phys. B: At. Mol. Opt. Phys. 34, R93-R130).

While more than a decade of work has provided glimpses into the physics of highly charged ion (HCI) neutralization on surfaces, two prominent objectives remain unfulfilled: (1) a unified, quantitative model for separating the kinetic energy response of a wide range of materials classes from the effects of HCIs’ potential energy effects and (2) insertion of HCI technology(s) as a cost-effective processing tool in a high-volume market sector. The National Institute of Standards and Technology (NIST) electron beam ion trap (EBIT) facility has recently incorporated tools for preparing clean, atomically flat surfaces of single crystals from gold to tungsten to silicon and for depositing and patterning thin films that range from high resistivity oxides to transition metals like cobalt and nickel. Current activities are focused on utilizing this unique capability to simultaneously address both of the objectives above by employing technologically important magnetic multi-layer systems to perform transport measurements that provide new insight into the fundamental processes that occur during HCI–surface neutralization. Specifically, we are producing Magnetic Tunnel Junctions (MTJs) critical to both magnetic devices and incorporating HCIs in the processing recipe to adjust critical electronic properties that are currently inhibiting their advancement. In return, the electrical response of the tunnel junction to the HCI processing provides a novel approach to performing ensemble measurements of HCI–surface interactions. By varying the construction of the tunnel junction, critical tests of the role of electron density, densities of states and electronic structure in the HCI–surface charge exchange can be performed.

An EBIT can selectively create, in principle, any charge state of every naturally occurring element, has good control on atomic collision processes, and can produce nearly ideal conditions for the analysis of highly ionized plasmas of astrophysical importance. A microcalorimeter enables the broadband detection of x-ray emission with high energy resolution and near-unity quantum efficiency in the energy range wherein many cosmic x-ray sources emit the bulk of their energy (0.2 keV–10 keV). The combination (EBIT+ microcalorimeter) provides a powerful tool for laboratory studies of the atomic/plasma processes underlying the energy release mechanisms in cosmic x-ray sources. We briefly describe some early experiments with a microcalorimeter built by the Smithsonian Astrophysical Observatory (SAO) and deployed on the NIST EBIT. We also present some very recent observations with a more advanced microcalorimeter built by SAO that can obtain an energy resolution of 4.5 eV. The higher spectral quality produced by the new system will be useful in laboratory measurements of interest in x-ray astronomy.

The importance of the combination of electron beam ion trap (EBIT) spectroscopy with X-ray microcalorimeters in the field of astrophysics was discussed. X-ray astronomy involves heavily charged ion instruments , especially EBIT, to obtain improved quality atomic data. In this regard, the research program at the National Institute of Standards and Technology, which uses X-ray spectroscopic methods to study plasma and atomic physics, was also discussed.

X-rays originating from a series of the cascades after electron capture into highly excited Rydberg states have been observed from low energy, highly charged Kr q + ions ( q =27–36) colliding with neutral Ar atoms. The intensity ratio between L ( n =3→2) X-rays and the sum of M X-rays ( n =4→3, n =5→3, n =6→3, etc.) is drastically changed from Kr 27+ to Kr 28+ and constant for higher ion charge states ( q =29–36). This feature can be understood to be due to the metastable states formed during cascades after electron capture into Kr 27+ ions. This is also supported by time-dependent population calculations.

Extreme ultraviolet radiation emitted from highly-charged dysprosium ions was measured at the National Institute of Standards and Technology. The ions were created, trapped, and excited in an electron beam ion trap (EBIT), and the spectra were recorded with a flat-field grazing-incidence spectrometer in the wavelength range 3 nm to 17 nm. Tuning the electron beam energies between 1.2 keV and 2.0 keV resulted in a selection of Rb-like Dy29+ to Ni-like Dy38+ ions. Identification of strong n = 4-n = 4 transitions was achieved by collisional-radiative modeling of the EBIT plasma. A total of 64 spectral lines were recorded, including 54 new identifications.

This paper reviews some of the fundamental properties of highly charged ions, the methods of producing them (with particular emphasis on table-top devices), and their use as a tool for both basic science and applied technology. Topics discussed include: charge dependence and scaling laws along isoelectronic or isonuclear sequences (for wavefunction size or Bohr radius, ionization energy, dipole transition energy, relativistic fine structure, hyperfine structure, Zeeman effect, Stark effect, line intensities, linewidths, strength of parity violation, etc), changes in angular momentum coupling schemes, selection rules, interactions with surfaces, electron-impact ionization, the electron beam ion trap (EBIT), ion accelerators, atomic reference data, cosmic chronometers, laboratory x-ray astrophysics, vacuum polarization, solar flares, ion implantation, ion lithography, ion microprobes (SIMS and x-ray microscope), nuclear fusion diagnostics, nanotechnology, quantum computing, cancer therapy and biotechnology.

We have studied the spectrum of x-rays emitted when 130 and 200 keV kinetic energy hydrogen-like argon ions impact silicon dioxide surfaces. Specifically, we were interested in the mechanism for creation of K-shell holes in the silicon target atoms, which can be filled with the release of a 1.75 keV x-ray. Two mechanisms have been hypothesized for the vacancy transfer between the K-shells of silicon and argon atoms: `direct vacancy transfer' and `projectile-decay-product-mediated vacancy transfer'. To separate these mechanisms, we used a target with a metallic coating (preventing close collisions between Si and Ar but allowing x-ray transmission) and a target without such a coating. We found that x-ray photoionization is the dominant mechanism in both cases and measured an upper limit for the contribution from the `direct mechanism' on the uncoated sample. Furthermore, we measured the relative strengths of the Kα, Kβ and Kγ lines of the argon projectile as a function of kinetic energy and found satisfactory agreement with charge exchange and cascade model calculations.

Nanoscale dots created on the surface of a highly oriented pyrolitic graphite sample by individual highly charged xenon projectile ions were observed using an in-situ scanning tunneling microscope. This is the first time that such features have been created and imaged without exposure to air. The dots vary in size with the charge state of the ion, up to a diameter of 6.6 nm for Xe44+. The results are discussed in terms of the energy density deposited in the near surface region.

We report new observations of emission line intensity ratios of Fe XVII under controlled experimental conditions, using the National Institute of Standards and Technology electron beam ion trap (EBIT) with a microcalorimeter detector. We compare our observations with collisional-radiative models using atomic data computed in distorted wave and R-matrix approximations, which follow the transfer of the polarization of level populations through radiative cascades. Our results for the intensity ratio of the 2p6 1S0-2p53d 1P1 15.014 A line to the 2p6 1S0-2p53d 3D1 15.265 A line are 2.94 ± 0.18 and 2.50 ± 0.13 at beam energies of 900 and 1250 eV, respectively. These results are not consistent with collisional-radiative models and support conclusions from earlier EBIT work at the Lawrence Livermore National Laboratory that the degree of resonance scattering in the solar 15.014 A line has been overestimated in previous analyses. Further observations assess the intensity ratio of the three lines between the 2p6-2p53s configurations to the three lines between the 2p6-2p53d configurations. Both R-matrix and distorted wave approximations agree with each other and our experimental results much better than most solar and stellar observations, suggesting that other processes not present in our experiment must play a role in forming the Fe XVII spectrum in solar and astrophysical plasmas.

We have directly observed the ion cloud distribution in an electron beam ion trap using visible and ultraviolet fluorescence from lines in the ground term of Ar13+, Xe31+ and Xe32+ ions. Using a gated intensified charge coupled device camera, we have the capability to measure both static and dynamic ion cloud distributions. The images provide information about the trapped highly charged ions which is difficult to obtain by other methods. To demonstrate the usefulness of the technique, we took images of static ion clouds under different conditions and compared the distributions to a simple model. We also recorded time resolved images which show that we can monitor the relaxation of the ion cloud toward equilibrium when the trapping conditions are suddenly changed. The information provided by such measurements can be used to improve models of ion cloud dynamics and, combined with modeling, these techniques can help improve measurements of atomic data using electron beam ion traps.

With the ability to create cosmic plasma conditions in the laboratory it is possible to investigate the dependencies of key diagnostic X-ray lines on density, temperature, and excitation conditions that exist in astrophysical sources with X-ray optics and a high-resolution X-ray microcalorimeter. The same instrumentation can be coupled to scanning electron microscopes or X-ray fluorescence probes to analyze the elemental and chemical composition of electronic, biological, geological and particulate materials. We describe how our microcalorimeter and X-ray optics provide significantly improved capabilities for laboratory astrophysics and microanalysis.

We have measured the radiative lifetimes for the level of and the level of . These measurements were performed by monitoring the temporal behaviour of their associated radiative decays during magnetic trapping mode in an electron beam ion trap (EBIT). Our lifetime results, 8.7(5) ms for and 5.7(5) ms for , are compared with theory.

Spherically curved crystal spectrometers are demonstrated for use on an Electron Beam Ion Trap (EBIT) for the first time. Such spectrometers are characterized by high light collection efficiency and relative insensitivity to source position, simultaneously, giving them an advantage that no X-ray spectrometer previously used on an EBIT has had. One of the spectrometer crystals tested is composed of mica, giving it the additional advantage that it can be used with reasonable efficiency up to very high order, allowing spectra to span a broad wavelength range from 0.5 Angstroms to 20 Angstroms. Spectra from Ne-like barium and He-like argon are presented.

We have measured the damage caused by the impact of low velocity, highly charged ions on insulating surfaces. Atomic force microscopy allows us to observe directly the surface topography with nanometer resolution. Using constant velocity (100 keV) Xeq+ ions (25 ⩽ q ⩽ 50) impinging on mica, we observe damage caused by single ion impacts. Impact sites typically are circular hillocks. Within the range and accuracy of the data, the height and volume of the damaged regions are well approximated by a linear function of ion potential energy.

Using molecular dynamics simulations, we have studied the Coulomb explosion processes on silicon surfaces. Three different initial shapes of ion distributions are used to model the possible localized charge distributions generated in highly charged ion (HCI)-surface impact. The three distinct distributions include a hemispherical, a flat disk, and a long and thin cylindrical geometrical. At t = 0, 100 singly-charged Si ions are embedded in the Si(111) surfaces. In about 100 fs, the strong repulsive electrostatic forces in these three systems cause Coulomb explosions and thus create three different shapes of craters on the surfaces. All simulations are carried to 1.6 ps, at which point the size and shape of the craters are nearly stabilized. The detailed analysis of the ejected ions, atoms, and the substrates reveals the dynamical consequences of the different initial conditions. For these 100 ions, the differences in the total number of the ejected particles, ranging from 245 to 317 particles, appear to be determined by the initial shape of the ionized region and not by the initial repulsive energy restored in the charged region. Contrary to intuition, a long and thin cylindrical distribution is the most efficient pattern for ejecting particles. The underlying mechanism is that ions with this initial configuration transfer more energy to the surrounding atoms. In all three cases, the number of ejected neutral particles are much greater then the number of ions (6–10 times as many atoms as ions). Among the ejected particles, a small percent of particles are found to return the surface at a later time. The angular distribution of ejected particles are also analyzed. While the differences in the distributions of polar angle of the Si atoms of the three configurations is small, the differences in distributions of the ions portray a strong shape dependence in the polar angle.

A recent 15 parts-per-million (ppm) experiment on muonic hydrogen found a major discrepancy with QED and independent nuclear size determinations. Here we find a significant discrepancy in a different type of exotic atom, a medium-Z nucleus with two electrons. Investigation of the data collected is able to discriminate between available QED formulations and reveals a pattern of discrepancy of almost 6 standard errors of experimental results from the most recent theoretical predictions with a functional dependence proportional to Z^n where n=4. In both the muonic and highly charged systems, the sign of the discrepancy is the same, with the measured transition energy higher than predicted. Some consequences are possible or probable, and some are more speculative. This may give insight into effective nuclear radii, the Rydberg, the fine-structure constant or unexpectedly large QED terms., Comment: 6 pages. 2 tables

We report spectroscopic measurements of highly charged samarium and erbium performed at the National Institute of Standards and Technology (NIST) Electron Beam Ion Trap (EBIT). These measurements are in the extreme ultraviolet (EUV) range, and span electron beam energies from 0.98 keV to 3.00 keV. We observed 71 lines from Kr-like Sm$^{26+}$ to Ni-like Sm$^{34+}$, connecting 83 energy levels, and 64 lines from Rb-like Er$^{32+}$ to Ni-like Er$^{40+}$, connecting 78 energy levels. Of these lines, 64 in Sm and 60 in Er are new. Line identifications are performed using collisional-radiative modeling of the EBIT plasma. All spectral lines are assigned individual uncertainties, most in the $\sim$0.001 nm range. Energy levels are derived from the wavelength measurements., Comment: 26 pages, 4 tables, 4 figures

The transition probability for the ${3\mathrm{d}}^{45}$${\mathrm{D}}_{2}$${\ensuremath{\leftarrow}}^{5}$${\mathrm{D}}_{3}$ magnetic-dipole transition in Ti-like Xe (${\mathrm{Xe}}^{32+}$) has been measured using an electron-beam ion trap. The unusually weak dependence of the transition energy on nuclear charge Z, and the fact that the transition wavelength remains in the 320- to 400-nm range for 5492, makes this transition promising as a plasma diagnostic tool. Our measurement of the transition probability yields 465(30) ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, corresponding to a lifetime of 2.15(14) ms, in good agreement with the theoretical value of 2.4 ms.

We describe our newly modified beam line and present its performance in conjunction with the National Institute of Standards and Technology electron-beam ion trap. We find that, contrary to previously reported results from similar ion sources, the highest intensity time-averaged ion fluxes are achieved by letting the ions boil out of the trap in a continuous stream rather than periodically dumping the trap to produce a pulsed beam. We produced continuous beams of 3.0(6)×106 Xe44+ ions per second and lower flux beams of charge states up to Xe49+. Also, in pulsed mode, we created beams with very high peak flux, over 1010 Xe44+ ions per second.

Kr spectra from 300 nm to 460 nm produced in an electron-beam ion trap (EBIT) are reported in this work. The spectra include magnetic dipole (M1) transitions from Kr XXIII and Kr XXII, as well as electric dipole (E1) lines of Kr II and Kr III. Two new capabilities of the EBIT at the National Institute of Standards and Technology, time resolved data acquisition and extracted ion analysis, are used to aid in the charge state identification.

Coulomb explosions on silicon surfaces are studied using large-scale molecular-dynamics simulations. Processes under investigation begin by embedding a region consisting of 265--365 singly charged ${\mathrm{Si}}^{+}$ ions on a Si [111] surface. The repulsive electrostatic energy, initially stored in the charged region, leads to a local state with ultrahigh pressure and stress. During the relaxation process, part of the potential energy propagates into the surrounding region while the remainder is converted to kinetic energy, resulting in a Coulomb explosion. Within less than 1.0 ps, a nanometer-sized hole on the surface is formed. A full analysis of the density, temperature, pressure, and energy distribution as functions of time reveals the time evolution of physical properties of the systems related to the violent explosive event. A shock wave that propagates in the substrate is formed during the first stage of the explosion, 0100 fs. The speed of the shock wave is twice the average speed of sound. After the initial shock the extreme nonequilibrium conditions leads to ultrarapid evaporation of Si atoms from the surface. Qualitatively similar features are observed on a smaller scale when the number of initial surface charges is reduced to 100. Our simulations demonstrate the details of a process that can lead to permanent structure on a semiconductor surface at the nanoscale level. The work reported here provides physical insights for experimental investigations of the effects of slow, highly charged ions (Qg40, e.g.) on semiconductor materials.

The Electron Beam Ion Trap (EBIT) facility at the National Institute of Standards and Technology (NIST) is now operational and producing atomic physics data. This report gives an overview of the design, operation, and performance of our EBIT. A preview of some of the first atomic physics results is given to illustrate the capabilities of the facility.

An overview is given of recent activities at the NIST electron beam ion trap (EBIT) facility. The machine has been operational for almost three years. Important characteristics and demonstrated capabilities of our EBIT are presented. Selected results include experiments with trapped highly charged ions (X-ray and visible spectroscopy), and with extracted ions (ion-surface collision studies).

Signatures of multi-keV LMN dielectronic resonances in highly-charged 3d^n ions of tungsten were detected in the intensity ratios of extreme-ultraviolet magnetic-dipole lines within ground configurations. The measurements were performed with an electron beam ion trap at beam energies of about 6 keV. Large-scale collisional-radiative modeling incorporating magnetic sublevels of autoionizing levels showed the significance of anisotropy effects due to the monodirectional propagation of the electron beam. The observation method allows simultaneous resolved registration of dielectronic resonances from several ions., 5 figures; submitted to Phys. Rev. A

We characterize the effect of quantum interference on the line shapes and measured line positions in atomic spectra. These effects, which occur when the excited state splittings are of order the excited state line widths, represent an overlooked but significant systematic effect. We show that excited state interference gives rise to non-Lorenztian line shapes that depend on excitation polarization, and we present expressions for the corrected line shapes. We present spectra of 6,7 Li D lines taken at multiple excitation laser polarizations and show that failure to account for interference changes the inferred line strengths and shifts the line centers by as much as 1 MHz. Using the correct lineshape, we determine absolute optical transition frequencies with an uncertainty of

The direct radiative recombination (RR) to n=3, 4, and 5 levels and the resonant dielectronic recombination (DR) cross section involving 2p\ensuremath{\rightarrow}3d excitation of Sc-like barium ${\mathrm{Ba}}^{35+}$ and Ti-like barium ${\mathrm{Ba}}^{34+}$ are calculated and compared with a recent electron beam ion trap experiment at the National Institute of Standards and Technology. Assuming a fractional population of ${\mathrm{Ba}}^{35+}$ in the trap of about 30%, we obtain good agreement between theory and experiment for the cross section ratio \ensuremath{\sigma}(DR)/\ensuremath{\sigma}(RR)(n=4), as well as for \ensuremath{\sigma}(RR)(n=5)/\ensuremath{\sigma}(RR)(n=4). The result confirms again that the simple angular momentum averaged procedure can be effective in treating DR for heavy open-shell ions when the energy resolution is not high. A large, broad peak below 2 keV in the x-ray spectrum is being theoretically examined. \textcopyright{} 1996 The American Physical Society.

The design and operation of a beam line for transporting and charge‐to‐mass selecting highly charged ions extracted from the National Institute of Standards and Technology electron beam ion trap (EBIT) are described. This beam line greatly extends the range of experiments possible at this facility. Using the transport system, pure beams of low‐energy, highly charged ions up to Xe44+ have been produced with substantially higher fluxes than previously reported from an EBIT source. Design choices and computer modeling for the various components of the beam line are explained in detail.

This paper provides an updated review of the capabilities of the Electron Beam Ion Trap (EBIT) as an advanced light source for atomic spectroscopy. Recent developments extending the spectral range to over five orders of magnitude in wavelength are highlighted. Distinguishing features that make EBIT a powerful tool both for simplifying spectral analysis and for making precise and accurate measurements are discussed. Various limitations of the machine are also discussed, with the intent to provide an introductory guide for scientists who may be planning EBIT spectroscopy experiments for the first time.

We have searched for the existence of the permutation symmetric 1{ital s}2{ital s}{sup 1}{ital S} state of helium in an atomic beam. Such a state directly violates the symmetrization postulate (SP) of quantum mechanics and implies a breakdown of the Pauli exclusion principle. Our data constrain recent SP-violating models at the 5 ppm level. This is the first experiment to look systematically for an SP-violating state with no multiple occupancy of a quantum state.

We are using Fabry-Perot interferometry to study visible lines from highly-charged ions created and trapped within an electron beam ion trap (EBIT). The 3d 4 5 D 2 – 5 D 3 titanium-like barium (Ba 34+ ) line at 3932(2) A was recently measured in Ref. [1] (C.A. Morgan et al., Phys. Rev. Lett. 74 (1995) 1716) using a grating monochromator. We present preliminary Fabry-Perot spectra of this line with significantly improved resolution. The Doppler-broadened 1 A line width is consistent with an expected ion temperature of less than 1 keV. We discuss the possibility of resolving Zeeman splittings, and of using these visible lines as a diagnostic in high temperature, low density plasmas, like those that exist in tokamaks and the EBIT itself.

This paper surveys the ongoing physics experiments at the Electron Beam Ion Trap (EBIT) facility at NIST, with particular attention paid to the underlying physical principles involved. In addition, some new data on the performance of our EBIT are presented, including results related to the determination of the trap width, ion temperature, and number of highly charged ions in the trap.