Recombination of bare Bi83+ ions with electrons -: art. no. 012702

Electron-ion recombination of completely stripped Bi83+ has been investigated at the Experimental Storage Ring (ESR) of the GSI in Darmstadt. 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, the experimental result is well described by the theory for radiative recombination (RR). However, below 15 meV the experimental rate increasingly exceeds the RR calculation by up to a factor of 5.2. This puzzling enhancement phenomenon, which has already been observed at other storage rings and single-pass merged-beams setups, is reported here from the ESR and for a bare ion heavier than argon. The enhancement is insensitive to changes of the electron density, which in subsequent measurements was set to 1.6 X 10(6), 3.2 X 10(6), and 4.7 X 10(6) cm(-3). An additional variation of the magnetic guiding field of the electrons from 70 mT to 150 mT in steps of 1 mT resulted in oscillations with a period of 7.6 mT of the rate that are accompanied by considerable changes of the transverse electron temperature.