For about 120 years, the Atomic Spectroscopy Group at the National Institute of Standards and Technology (NIST) was one of the world leaders in experimental and theoretical atomic and plasma spectroscopy, production of standard reference data for atomic parameters, and development of atomic databases. Nonetheless, in early 2025 the group was abruptly terminated due to the apparent change of priorities for NIST research. Fortunately, the whole ASG scientific and engineering team was soon adopted by NASA Goddard Space Flight Center and the University of Maryland College Park which allowed us to preserve its rich legacy and offer new opportunities. We will briefly describe the achievements and status of the group at this pivotal moment of its history as well as its research plans for the near future.

The atomic processes in laser-produced tin plasmas for the extreme ultraviolet light sources are investigated. The level population of complex tin ions is calculated using the collisional-radiative (CR) model, and then spectral emissivity and opacity are calculated, taking the spectral structure of unresolved transition array into account. A rule-based method for developing a large-scale CR model is discussed, which enables the simulation of the emission spectrum using a relatively compact model. The effect of configuration interaction on the wavelength of the emission and broadening of the main peak at λ = 13.5 nm by the emission from multiply excited states is discussed.

The advent of the X-ray microcalorimeter spectrometer Resolve onboard the XRISM space telescope opened a new era for high-resolution X-ray spectroscopy of astrophysical plasmas. Many spectral features were newly detected, including the Kα and Kβ inner-shell transition lines of mildly ionized (F- to Li-like) Fe at 6–8 keV in the spectra of X-ray binaries and active galactic nuclei. The widely used atomic databases contain information on the Kα but not Kβ lines of these ions. We conducted the atomic structure calculation using FAC to derive the Fe Kα and Kβ lines and verified the result against ground experiments and other calculations of the Fe Kα lines. We then implemented the Fe Kβ lines in a radiative transfer code (Cloudy) and compared the synthesized and observed spectra with XRISM. A reasonably good agreement was obtained between the observation and the ab initio calculations. This exemplifies the need to expand the atomic databases to interpret astrophysical spectra.

We present the basic performance and experimental results of an electron beam ion trap (JAXA-EBIT), newly introduced to the Japanese astronomical community. Accurate atomic data are indispensable for the reliable interpretation of high-resolution X-ray spectra of astrophysical plasmas. The JAXA-EBIT generates highly charged ions under well-controlled laboratory conditions, providing experimental benchmarks for atomic data. The JAXA-EBIT shows performance comparable to the Heidelberg compact EBIT through dielectronic recombination measurements of highly charged Ar ions. Furthermore, we conducted resonant photoexcitation spectroscopy of highly charged ions using the soft X-ray beamline BL17SU at the synchrotron radiation facility SPring-8. As a result, we successfully detected resonance transitions of He-like O⁶⁺ and Ne-like Fe¹⁶⁺. These results demonstrate the capability of the JAXA-EBIT for precise measurement of atomic data and show that it serves as a powerful tool for advancing astrophysical research.

Short-wavelength lasers based on a transient collisional excitation (TCE) have extensively been studied using neon (Ne)-like and nickel (Ni)-like ions. In this study, we have examined the possibility of amplified spontaneous emission (ASE) at 111.9 nm in a Ne-like aluminum (Al) plasma using the TCE scheme. Al targets in vacuum were irradiated with two time-delayed Nd:YAG laser pulses (wavelength: 1,064 nm). A pre-pulse laser generated a pre-formed plasma, and subsequently a grazing-incidence main-pulse laser axially heated it to excite 3p (1S⁰)–3s (1P¹) transition of Al³⁺ ion. To achieve effective energy deposition in the region of electron density of ∼ 10¹⁸ cm⁻³, the main-pulse was introduced at 3.5° incidence angle. Under optimized conditions, a sharp spectral line at 111.9 nm, corresponding to the 3p–3s lasing transition in Ne-like Al ion, was observed. Although clear ASE was not observed, this work confirms the feasibility of vacuum ultraviolet (VUV) ASE generation by means of this scheme. Further improvements in pulse synchronization and irradiation conditions would show the prominent evidence of 111.9-nm ASE phenomenon.

The discovery of gravitational waves (GW170817) and the associated kilonova (AT2017gfo) from a neutron star merger in 2017 confirmed the latter as key sites for heavy element production through the r-process. Subsequent observations, including late-time spectra with JWST, have highlighted the need for accurate modeling of kilonova ejecta. In the photospheric phase, atomic level populations can be estimated under LTE using Boltzmann and Saha relations, but about a week after the merger the ejecta enters the nebular phase where non-LTE effects dominate. Modeling nebular spectra therefore requires a detailed treatment of radiative and collisional processes that affect the population of atomic levels. This work focuses on electron-impact excitation in Sr II, a heavy ion relevant for kilonova spectra. Two computational approaches are employed: the Plane-Wave Born approximation within the pseudo-relativistic Hartree-Fock method, and a Distorted Waves method using AUTOSTRUCTURE. The resulting collision strengths are compared against reference R-matrix data to evaluate the accuracy of these approximations and their suitability for large-scale applications to all heavy elements. In addition, radiative parameters for forbidden transitions are computed. These results provide an essential benchmark of approximations that could be used to compute atomic data for nebular-phase kilonova modeling.

In the past few decades, X-ray astronomy satellites equipped with grating spectrometers and microcalorimeters have enabled high-resolution spectroscopic observations of astrophysical objects. The need for accurate atomic data has arose as we attempt detailed analysis of the high-resolution spectra they provide. This is because current spectral models, which heavily rely on theoretical calculations, entail non-negligible uncertainties. We employ a plasma spectroscopy device called electron beam ion trap (EBIT) to experimentally obtain precise atomic data. An EBIT with a design that allows combined operation with synchrotron radiation facilities was developed based on the Heidelberg Compact EBIT and installed at ISAS/JAXA for this purpose. We conducted a spectroscopic experiment using the JAXA-EBIT at the synchrotron radiation facility SPring-8, and successfully obtained high-resolution spectra of the Lα resonance transition of Ne-like Fe¹⁶⁺ ions, 3C, as well as the Kα resonance transition of He-like O⁶⁺ ions. We also measured another Ne-like Fe¹⁶⁺ Lα resonance transition, 3G, and constrained an upper limit of the oscillator strength ratio of 3G to 3C, using our experimental results. The experimental values obtained in this study will be applied to observational studies of astrophysical objects as a part of the plasma spectral modeling.

^*This article is based on the presentation selected as APiP2025 Best Student Poster.

In this paper, we use the Halfium R-matrix method to investigate the Rydberg states of the H₂ molecule up to n = 20, filling the gap above the low-lying bound states already calculated with configuration interaction packages. Moreover, we show that the use of Quantum Defect Theory scaling laws, allows for a comprehensive analysis of the regular patterns resulting from the coupling between Rydberg series and doubly excited states. The results should open the door for more efficient quasi-diabatization of the potential energy curves which is required for calculating cross sections and rate coefficients of the (e + H₂⁺) collisional processes, involved in the plasma modeling for fusion devices.

Laser-produced tin (Sn) plasma is extensively used as an extreme ultraviolet (EUV) light source for advanced lithography; however, the collector mirror lifetime is considerably shortened by high-energy debris from the plasma. The introduction of hydrogen (H₂) gas into the plasma region can mitigate debris through ion–neutral collisions and chemical reactions forming gaseous stannane (SnH₄). However, the detailed Sn-H interaction mechanisms remain uninvestigated. Herein, visible emission spectroscopy was used to investigate the spatiotemporal behaviors of Sn and H plasmas generated by 12-ps, 1,064-nm laser pulses incident on a solid Sn target in a 100 Pa H₂ atmosphere. Spatiotemporal-resolved measurements of H_α and H_β lines revealed prompt hydrogen excitation following plasma generation, with electron temperatures of 1–2 eV and electron densities up to 1 × 10¹⁷ cm⁻³ near the target. These conditions aid the formation of hydrogen radicals that react with Sn atoms/ions to produce SnH₄, contributing to the effective mitigation of debris. These findings offer insights into the optimization of the EUV source performance and the prolongation of the optical component lifetime.

We calculated adiabatic states of atomic hydrogen in strong magnetic fields treating the radial distance of the spherical coordinates as the adiabatic parameter. The results show a transition from diamagnetic Kepler motion in the inner region to gyromotion along the magnetic field at large distances. At the boundary, avoided crossings of adiabatic potential curves occur along the ridge of the diamagnetic potential, indicating strong local non-adiabatic coupling. These findings clarify the mixed Coulomb-magnetic dynamics of hydrogen and contribute to more accurate modeling of atomic processes in strongly magnetized astrophysical environments.

^*This article is based on the presentation selected as APiP2025 Best Student Poster.

Understanding hydrogen trapping in tungsten is crucial for accurate modeling of plasma-wall interactions in fusion devices. In this study, we developed a deep learning model to predict hydrogen trapping sites, which serve as essential input parameters for kinetic Monte Carlo (kMC) simulations. The model employs a U-Net–based convolutional neural network that directly maps three-dimensional potential energy distributions to trapping site positions. Training data were generated from atomistic calculations using the embedded atom method (EAM) potential, and ground-truth trapping sites were systematically identified by force relaxation. The trained model achieved an F1 score of approximately 0.76, with most predicted sites coinciding with the true minima within ± 1 voxels (1 voxel = 0.1 Å per side). Visual comparisons confirmed the ability of the model to capture both global and local features of the potential energy landscape. In terms of efficiency, the proposed approach reduced prediction time by more than three orders of magnitude compared with conventional force-relaxation searches, enabling predictions in less than one second on a GPU. These results demonstrate that deep learning provides an accurate and computationally efficient method for identifying trapping sites. Future extensions include incorporating more complex defect structures and integrating the model into molecular dynamics-kMC hybrid frameworks for large-scale plasma-wall interaction simulations.

The article reports electron-impact excitation cross-sections and rate coefficients for neutral tungsten for three transitions (400.87, 429.46, and 430.21 nm) using the relativistic distorted wave approach within the flexible atomic code. Some of these lines are also observed in tokamak plasma. Cross-sections are computed for incident electron energy up to 30 keV. The energy levels in flexible atomic code were corrected to match the NIST database. The electron impact excitation rate coefficients are also provided.