arXiv subjects

Alexander Borovik Jr.

Publications and source records attributed to Alexander Borovik Jr..

3 recordsLinked to original sources

arXiv2026

Commissioning of a fast fine-step electron-energy-scan system for electron-ion crossed-beams experiments

We report on the commissioning of a fast electron-energy scan system for measurements of electron-impact ionization cross sections. The Giessen crossed-beams experiment employs a high-power electron gun which has been developed over recent years and which permits wide variations of the beam parameters. A multi-electrode design enables the decoupling of the electron energy from the electron density. The newly implemented control system, which governs the various electrode potentials, is described together with the salient technical features.

physics.atom-ph↗

arXiv2019

Electron-impact single ionisation of W14+ ions: Subconfiguration-average and level-to-level distorted wave calculations

The cross section for electron-impact single ionisation of W14+ ions has been calculated by using two different approaches, i.e., the subconfiguration averaged distorted-wave (SCADW) method and the more involved level-to-level distorted-wave (LLDW) method. Both methods are found to yield very similar results except for the 4d->5d excitation-autoionisation (EA) channels that straddles the ionisation threshold. Accordingly, a hybrid theoretical cross section where the $4d\to 5d$ EA SCADW cross section is replaced by its LLDW counterpart is in good agreement with the experimental result from an electron-ion crossed-beams experiment. This is in contrast to pure SCADW calculations for W14+ and neighbouring charge states which exhibit significant deviations from the experimental near-threshold cross sections of Schury et al. [J. Phys. B 53 (2020) 015201].

physics.atom-ph↗

arXiv2019

EBIT Observation of Ar Dielectronic Recombination Lines Near the Unknown Faint X-Ray Feature Found in the Stacked Spectrum of Galaxy Clusters

Motivated by possible atomic origins of the unidentified emission line detected at 3.55 keV to 3.57 keV in a stacked spectrum of galaxy clusters (Bulbul et al. 2014), an electron beam ion trap (EBIT) was used to investigate the resonant dielectronic recombination (DR) process in highly-charged argon ions as a possible contributor to the emission feature. The He-like Ar DR-induced transition 1s$^2$2l - 1s2l3l$^\prime$ was suggested to produce a 3.62 keV photon (Bulbul et al. 2014) near the unidentified line at 3.57 keV and was the starting point of our investigation. The collisional-radiative model NOMAD was used to create synthetic spectra for comparison with both our EBIT measurements and with spectra produced with the AtomDB database/Astrophysical Plasma Emission Code (APEC) used in the Bulbul et al. (2014) work. Excellent agreement was found between the NOMAD and EBIT spectra, providing a high level of confidence in the atomic data used. Comparison of the NOMAD and APEC spectra revealed a number of missing features in the AtomDB database near the unidentified line. At an electron temperature of $T_e$ = 1.72 keV, the inclusion of the missing lines in AtomDB increases the total flux in the 3.5 keV to 3.66 keV energy band by a factor of 2. While important, this extra emission is not enough to explain the unidentified line found in the galaxy cluster spectra.

astro-ph.HE↗