  Dielectronic recombination (DR) of xenonlike W20+ forming W19+ has been
studied experimentally at a heavy-ion storage-ring. A merged-beams method has
been employed for obtaining absolute rate coefficients for electron-ion
recombination in the collision energy range 0-140 eV. The measured rate
coefficient is dominated by strong DR resonances even at the lowest
experimental energies. At plasma temperatures where the fractional abundance of
W20+ is expected to peak in a fusion plasma, the experimentally derived plasma
recombination rate coefficient is over a factor of 4 larger than the
theoretically-calculated rate coefficient which is currently used in fusion
plasma modeling. The largest part of this discrepancy stems most probably from
the neglect in the theoretical calculations of DR associated with
fine-structure excitations of the W20+([Kr] 4d10 4f8) ion core.
