High-resolution charge-exchange spectroscopy of Si$$^{13+/14+}$$ ions with an X-ray microcalorimeter

Abstract Charge exchange between highly charged ions and neutral atoms at collision energies in the keV range occurs in many astrophysical environments. Modeling this quasi-molecular process is difficult, and accurate laboratory data are scarce. We report charge-exchange measurements of highly charged silicon ions using a superconducting transition-edge X-ray microcalorimeter with an energy resolution of approximately 2 eV FWHM at the Si K $$_\alpha$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mi>α</mml:mi> <mml:mrow/> </mml:mmultiscripts> </mml:math> energy and an electron beam ion trap. By using its magnetic trapping mode, i. e, cyclically turning the electron beam on and off, we isolate charge-exchange–induced emission and distinguish radiative cascade features unresolved with semiconductor detectors. These measurements can help isolating their contributions to the X-ray spectra of hot astrophysical plasmas from the dominant thermal excitation mechanisms, in particular for Rydberg states of the highly charged ions. Additionally, we present high resolution spectra of the Si Li-like K $$_\beta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mi>β</mml:mi> <mml:mrow/> </mml:mmultiscripts> </mml:math> - to K $$_\epsilon$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mi>ϵ</mml:mi> <mml:mrow/> </mml:mmultiscripts> </mml:math> -transitions observed during the beam-on phase.