Dielectronic recombination of lithiumlikeNi25+ions: High-resolution rate coefficients and influence of external crossed electric and magnetic fields

Abstract

Absolute dielectronic recombination (DR) rates for lithiumlike Ni 25+ (1s 2 2s) ions were measured at high-energy resolution at the Heidelberg heavy-ion storage ring TSR. We studied the center-of-mass energy range 0-130 eV which covers all ∆n=0 core excitations. The influence of external crossed electric (0-300 V/cm) and magnetic (41.8-80.1 mT) fields was investigated. For the measurement at near-zero electric field resonance energies and strengths are given for Rydberg levels up to n=32; also Maxwellian plasma rate coefficients for the ∆n=0 DR at electron temperatures between 0.5 and 200 eV are provided. For increasing electric field strength we find that for both the 2p 1/2 and the 2p 3/2 series of Ni 24+ (1s 2 2pjnℓ) Rydberg resonances with n > 30 the DR rate coefficient increases approximately linearly by up to a factor of 1.5. The relative increase due to the applied electric field for Ni 25+ is remarkably lower than that found in previous measurements with lighter isoelectronic Si 11+ , Cl 14+ and also Ti 19+ ions, [T. Bartsch et al, Phys. Rev. Lett. 79, 2233(1997 82, 3779 (1999) and to be published] and in contrast to the results for lighter ions no clear dependence of the electric field enhancement on the magnetic field strength is found. The Maxwellian plasma rate coefficients for ∆n=0 DR of Ni 25+ are enhanced by at most 11% in the presence of the strongest experimentally applied fields.

Experimental Mg IX photorecombination rate coefficient

“…Various aspects of recombination measurements at the heavy-ion storage ring TSR of the Max-Planck-Institut für Kernphysik (MPI-K) in Heidelberg, Germany, have been described by Kilgus et al (1992), Lampert et al (1996), Pastuszka et al (1996), Müller & Wolf (1997), and Schippers et al (2000Schippers et al ( , 2001. For the present experiment a Mg  ion beam with an energy of about 4.2 MeV/u was provided by the MPI-K linear accelerator facility and injected into the storage ring.…”

Dielectronic recombination data for dynamic finite-density plasmas

“…dominate the dielectronic recombination process can be Starkmixed by weak electric fields (Burgess & Summers 1969), in particular the plasma microfield (Jacobs et al 1976), and so increase the partial rate coefficients by factors of 2, or 3, or more, over a wide range of n. Recently, the picture has been further complicated by the discovery that magnetic fields, when crossed with an electric field, strongly affect the electric field enhancement -by reducing it in most cases(see Robicheaux et al 1997;Bartsch et al 1999;Schippers et al 2000;Böhm et al 2001). While this suppression of the electric field enhancement is advantageous towards the use of field-free dielectronic recombination data, it is disadvantageous in terms of trying to compute field-dependent data for plasma modelling.…”

Dielectronic recombination data for dynamic finite-density plasmas

“…The effects of external electric fields on dielectronic recombination are found to be quite significant by Griffin et al (1986) in their studies of Na-like ions P 4+ , S 5+ , Cl 6+ and by Griffin & Pindzola (1987) in their studies of Fe 15+ . Recent experimental (Bartsch et al 1997(Bartsch et al , 1999Böhm et al 2001Böhm et al , 2002Schippers et al 2000;Gwinner et al 2000), and theoretical studies (Robicheaux & Pindzola 1997;Robicheaux et al 1998;Griffin et al 1998;Mitnik et al 1999) have shown the importance of the effects of crossed external electric and magnetic fields. We expect that low charge Na-like ions will be more sensitive to the external fields, as is the case for Li-like ions (Badnell et al 1993).…”