Dielectronic recombination of xenonlike tungsten ions

Abstract

Dielectronic recombination (DR) of xenonlike ${\mathrm{W}}^{20+}$ forming ${\mathrm{W}}^{19+}$ 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 ${\mathrm{W}}^{20+}$ 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 ${\mathrm{W}}^{20+}$([Kr]$4{d}^{10} 4{f}^{8}$) ion core.