Populating high-n Rydberg states in highly-charged Ar ions*

Rydberg Highly Charged Ions (RyHCI) are interesting systems to study as they provide excellent test beds for precision tests of quantum electrodynamics and precision x-ray wavelength standards. Moreover, certain high angular momentum states are considered to be potentially useful for measuring fundamental constants. Dielectronic Recombination (DR) is a significant process that results in the production of Rydberg states. DR is a process in which a free electron is captured by an ion, non-radiatively, by exciting a bound electron in the ion. DR is a resonant process, occurring only at specific free electron energies. The resulting doubly excited ion then radiatively decays.

Experiments were conducted at the National Institute of Standards and Technology's (NIST) Electron Beam Ion Trap (EBIT) facility utilizing the Transition Edge Sensing (TES) microcalorimeter [1]. We present highly charged Ar x-ray spectra as a function of the electron beam energy that show the signatures of different processes populating electronic levels including DR. We measure DR cross-sections to compare with the absolute, precisely measured radiative recombination (RR) cross-sections as well as to compare with theoretical cross-sections. These measurements are expected to be valuable diagnostics for many areas of plasma physics.

[1]    P. Szypryt, et al. Rev. Sci. Instrum 90, 123107 (2019)