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Abstract We show the effects of ladder ionization and hyperfine quenching on charge state distributions and spectral features of ions in electron beam ion trap (EBIT) devices. Ladder ionization with intermediate excitation of metastable states proceeds at lower than ionization potential electron beam energies, while hyperfine quenching reduces the lifetimes of these states by enhancing particular decay channels through nuclear-electronic coupling. Using Ni-like Pr and Nd ions, we show that these processes significantly alter ion populations and spectra, emphasizing the importance of incorporating hyperfine level specific modeling in EBIT studies. 

Abstract Electron beam ion traps (EBITs) are compact devices optimized for producing ions in high charge states for spectroscopic studies or as extracted beams. Key characteristics, such as current density and electron-ion overlap, govern ionization and excitation rates. Using visible and X-ray imaging of emissions from highly charged ions, the spatial distributions of the electron beam and ion cloud in the Smithsonian Astrophysical Observatory (SAO) EBIT were measured, enabling the determination of the effective electron density. The nominal electron beam full width at half maximum (FWHM) was determined to be 92.0 ± 9.7 μm, while the ion cloud FWHM was 410.5 ± 16.5 μm, indicating an effective electron density roughly an order of magnitude lower than determined geometrically. The effects of magnetic fields on the electron beam size were also investigated, demonstrating sensitivity to the focusing magnet and bucking coil currents. These findings emphasize the need for simultaneous measurement of the effective electron density to improve the accuracy of density-sensitive studies in EBIT systems. 

Abstract In this report we describe the design and operation of the electron beam ion trap (EBIT) at the Smithsonian Astrophysical Observatory (SAO). We also provide an overview of recent upgrades that have led to improved system stability and greater user control, increasing the scope of possible experiments. Observations of X-ray emission from background elements were made after the system upgrades. The evolution of the spectrum, produced at beam energies ranging from 1285 eV to 3095 eV, allowed us to identify emission from multiple charge states and from key processes, such as dielectronic recombination, in Ba and Si ions. Emission from these background elements was easily removed by periodically dumping the trap every 2 s or less. 

Abstract Charge-exchange recombination with neutral atoms significantly influences the ionization balance in electron beam ion traps (EBIT) because its cross section is relatively large compared to cross sections of electron collision induced processes. Modeling the highly charged ion cloud requires the estimate of operating parameters, such as electron beam energy and density, the density of neutral atoms, and the relative velocities of collision partners. Uncertainty in the charge-exchange cross section can dominate the overall uncertainty in EBIT experiments, especially when it compounds with the uncertainties of experimental parameters that are difficult to determine. We present measured and simulated spectra of few-electron Fe ions, where we used a single charge-exchange factor to reduce the number of free parameters in the model. The deduction of the charge-exchange factor from the ratio of Li-like and He-like features allows for predicting the intensity of H-like lines in the spectra. 

Abstract We describe a novel technique to determine absolute nuclear radii of high-Znuclides. Utilizing accurate theoretical atomic structure calculations together with precise measurements of extreme ultraviolet transitions in highly charged ions this method allows for precise determinations of absolute nuclear charge radii based upon the well-known nuclear radii of their neighboring elements. This method can work for elements without stable isotopes, and its accuracy may be competitive with current methods (electron scattering and muonic x-ray spectroscopy). 

We report on a method for determining the absolute nuclear charge radius of high- $Z$elements using extreme-ultraviolet spectroscopy of highly charged Na-like ions in tandem with highly accurate atomic structure calculations of transition energy differences. The application of this method has reduced the nuclear charge radius uncertainty of ${}^{191}\mathrm{Ir}$by a factor of 8 from the currently accepted literature value, with a recently reported charge radius of 5.435(12) fm. The result reduces the charge radius uncertainty along the full Ir isotopic chain when combined with prior optical isotope shift measurements. The technique utilizes only a few million ions stored in an ion trap, which should apply to measurements with small quantities of radioactive nuclei. Published by the American Physical Society2025