Recombination of lithium-like bismuth and uranium ions with free electrons at the ESR

In two separate experiments at the ESR recombination of 230 MeV/u Bi80+ and 170 MeV/u U89+ ions was studied. The analysis of these experiments has been carried on in order to extract information about radiative recombination (RR) of very highly charged ions exposed to electrons with a density of few 10(6) cm(-3). In the light of the recombination rate enhancement seen in almost all recent experiments at a relative energy E-rel = 0 eV, a surprising result is found for the very highly charged ions, which could add some confusion to an already puzzling picture: in spite of the high charge state of the investigated ions there is no evidence of enhanced recombination beyond the expected RR rate. This observation appears to be supported by other experimental findings at the ESR as well. We suspect, however, that this is a consequence of excessive transverse magnetic field components in the ESR cooler (which have meanwhile been corrected for) causing variable degrees of angular mismatch between the ion beam and the electron beam occurring when the ring settings are tuned for optimum cooling.