Electron-ion collision spectroscopy at the CRYRING@ESR electron cooler

TL;DR

This paper details the setup and initial results of electron-ion collision spectroscopy at CRYRING@ESR, enabling precise tests of quantum electrodynamics with heavy ions through measurements of recombination processes.

Contribution

It introduces a new experimental setup at CRYRING@ESR for electron-ion collision spectroscopy and presents first experimental results on recombination of berylliumlike lead ions.

Findings

Recombination rate enhancement factor of 3.5 at zero collision energy.

Excellent agreement with shifted theoretical predictions for resonant recombination.

First detailed experimental data on electron-ion recombination at CRYRING@ESR.

Abstract

Electron-ion collision spectroscopy at heavy-ion storage rings aims at precision measurements of resonance features that occur in the cross sections of electron collision processes such as electron-impact ionization of ions or electron-ion recombination. As part of the international FAIR project, the low-energy ion storage ring CRYRING@ESR has been coupled with the heavy-ion accelerators operated by the GSI Helmholtz Center for Heavy-Ion Research in Darmstadt, Germany. This has created a new opportunity for stringent tests of strong field quantum electrodynamics by electron-ion collision spectroscopy of heavy few-electron ions. The present contribution provides details of the electron-ion collision spectroscopy setup at CRYRING@ESR and of the associated data-analysis procedures along with first results for nonresonant and resonant recombination of berylliumlike lead ions. For nonresonant recombination a recombination rate enhancement factor of 3.5 is found at zero electron-ion collision energy. For resonant recombination there is excellent agreement with recent theoretical results when these are shifted by 340~meV in energy.