Radiative recombination of bare Bi83+: Experiment versus theory

TL;DR

This study measures and compares the radiative recombination rates of bare Bi83+ ions with theoretical predictions, revealing good agreement at higher energies and significant enhancement at near-zero energies, with magnetic field effects observed.

Contribution

First experimental investigation of electron-ion recombination for a bare heavy ion (Bi83+), providing data to compare with theoretical models and revealing unexplained low-energy enhancements.

Findings

Good agreement between experiment and theory from 15 meV to 125 eV

Significant recombination rate enhancement below 15 meV

Magnetic field variations cause oscillations in recombination rates

Abstract

Electron-ion recombination of completely stripped Bi83+ was investigated at the Experimental Storage Ring (ESR) of the GSI in Darmstadt. It was the first experiment of this kind with a bare ion heavier than argon. Absolute recombination rate coefficients have been measured for relative energies between ions and electrons from 0 up to about 125 eV. In the energy range from 15 meV to 125 eV a very good agreement is found between the experimental result and theory for radiative recombination (RR). However, below 15 meV the experimental rate increasingly exceeds the RR calculation and at Erel = 0 eV it is a factor of 5.2 above the expected value. For further investigation of this enhancement phenomenon the electron density in the interaction region was set to 1.6E6/cm3, 3.2E6/cm3 and 4.7E6/cm3. This variation had no significant influence on the recombination rate. An additional variation of the magnetic guiding field of the electrons from 70 mT to 150 mT in steps of 1 mT resulted in periodic oscillations of the rate which are accompanied by considerable changes of the transverse electron temperature.