Dielectronic recombination of xenonlike tungsten ions

Abstract

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.Comment: 7 pagers, 4 figures, accepted for publication in Physical Review

Level-resolved quantum statistical theory of electron capture into many-electron compound resonances in highly charged ions

“…Experiment shows that the recombination rates at low (∼ 1 eV) electron energies in these ions exceed the direct RR rates by two orders of magnitude or more. At the same time the measured rates do not show the sharp resonance structure normally associated with DR [14,19,36]. The MBQC statistical theory quantitatively explains the discrepancy as being due to a very dense spectrum of compound resonances: multiply excited, strongly mixed, chaotic many-electron eigenstates.…”

“…In the future our levelresolved statistical theory can also be applied to other processes where chaotic mixing plays an important role, such as photo-and electron-impact ionization and scattering processes in highly charged ions [20]. [14] (black) and the theoretical results of this paper (red). The latter is obtained by multiplying our capture rate (dot-dashed line) with our extracted fluorescence yield (18).…”

“…In Fig. 4 we also include the experimental recombination data of [14]. Since in this paper we have neglected the fluorescence yield, a direct comparison cannot be made except very close to threshold, ε 1 eV, where the radiative yield should be very close to unity.…”

“…We will consider one of these processes in detail: the recombination of W 20+ with an incident electron to form W 19+ [14]. Tungsten is a major candidate for the plasma facing components of ITER and future fusion reactors, and processes involving highly-charged tungsten ion are critical for the properties of fusion plasmas [15].…”

Effect of an external magnetic field on the determination of E1M1 two-photon decay rates in Be-like ions

“…The 2s 2p 3 P 0 state is the lowest excited state, and for isotopes with a nonzero nuclear spin, the J = 0 → 0 transition channel * jon.grumer@teorfys.lu.se opens up due to mixing of the hyperfine levels, leading to a so-called hyperfine-induced transition (HIT). Such a shortening of lifetimes of metastable states owing to hyperfine interaction is referred to as hyperfine quenching and has been investigated for Be-like ions both theoretically [15][16][17][18][19][20] and experimentally [21,22]. For isotopes with zero nuclear spin, on the other hand, a one-photon transition to the ground state 2s 2 1 S 0 is strictly forbidden in a field-free region, and the lowest-order decay channel is a very slow E1M1 two-photon process.…”