Istvan Orban

First results from the Stockholm Electron Beam Ion Trap

A new laboratory for highly charged ions is being built up at Stockholm university. An electron beam ion trap (EBIT) (3T magnet,≤30 keV electron beam) was installed. It is used for spectroscopic studies, precision mass measurements, electron ion collisions, and highlycharged ion surface studies. Here we report about a fast ion-extraction scheme from ebit and first results using a time-of-flight detection as well as a labview based operational system of ebit.

Spectroscopic study of doubly excited states in Mg-like Si using dielectronic recombination

We present calculated and experimentally derived electron–ion recombination rate coefficients for Na-like Si IV, recombining into Mg-like Si III, and provide accurate spectroscopic data for doubly excited states located above the ionization threshold of Si III. The experimental recombination rate coefficients were measured in a merged-beam-type experiment at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm. Changing the electron–ion relative energy from 0 to 20 eV we covered the energy region from the first to the third ionization threshold. We find that even for the low-charged Si2+ ion, a relativistic many-body perturbation theory calculation is necessary, to describe the recombination rate coefficients in the low-energy region, up to 1.5 eV, satisfactorily. Doubly excited states, forbidden to form in LS coupling, are responsible for the most prominent dielectronic recombination resonances at low energies and contribute with 40% to the strength. Several wide resonances give rise to a plateau-like formation in the recombination spectrum. A broader energy range, up to 6.7 eV, was covered with a non-relativistic many-body calculation. This range contains, in addition to 3pnl resonances, several resonances of the type 3dnl, with the LS-forbidden 3d23F states giving rise to a strong, isolated peak at 2.976 eV. The NIST database lists eleven doubly excited states of Si III with energy positions deviating considerably from our determination. Since the listed lines are also not fully matching those with the largest fluorescence yields it must be concluded that they are misidentified.

Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III

Aims. Absolute, total recombination rate coefficients for Si iv were determined using the CRYRING heavy-ion storage ring.Calculated rate coefficients were used to estimate recombination into states ...

Photo-recombination studies at R-EBIT with a Labview control and data acquisition system

Equipment at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) was developed for photo-recombination studies. A LabView-based event mode data acquisition and R-EBIT control system was impl ...

Recombination rate coefficients of Be-like Si

Aims. Merged-beam and plasma recombination rate coefficients for Be-like Ne vii were extracted from results of a merged-beam type experiment. Methods. The cryring heavy-ion storage ring was used to determine merged-beam recombination rate coefficients for Be-like Ne 6+ . Recombined Ne 5+ ions were separated from the stored beam in the first dipole magnet following the electron-ion interaction region. Field-ionization at this dipole magnet prevented detection of recombination into states with the principal quantum number n > ncutoff = 23. To account for the field-ionization effects, results obtained with autostructure calculations were used for recombination channels above ncutoff. The merged-beam recombination rate coefficients were then convoluted with Maxwellian electron energy distributions in the 10 3 −3 × 10 6 K temperature region, to obtain plasma recombination rate coefficients. Results. Good agreement was found between the experimentally derived rate coefficient spectrum and results of the autostructure calculation. At low energies, several strong dielectronic recombination resonances belonging to the spin-forbidden 2s2p( 3 PJ)nl series dominate the merged-beam spectrum. Recombination through these states dominates at low-temperatures, e.g. at 10 3 K recombination through these resonances is more than one order of magnitude higher than the radiative recombination rate coefficient. Most data from the literature significantly underestimate the low-temperature plasma rate coefficients below 10 4 K, with only two calculations showing rate coefficients comparable to our results. Strong contributions from trielectronic recombination were found in the merged-beam spectrum of Be-like Ne, associated with double excitation of the Be-like Ne core, during the attachment of the free electron. Calculated trielectronic recombination resonance positions agree with experimental peaks, however compared to the experiment, the calculation underestimates the strength of trielectronic recombination.

Experimental dielectronic recombination rate coefficientsfor Na-like S VI and Na-like Ar VIII

Aims. Absolute recombination rate coefficients for two astrophysically relevant Na-like ions are presented. Methods. Recombination rate coefficients of S vi and Ar viii are determined from merged-beam type experiments at the CRYRING electron cooler. Calculated rate coefficients are used to account for recombination into states that are field-ionized and therefore not detected in the experiment. Results. Dielectronic recombination rate coefficients were obtained over an energy range covering Δn = 0 core excitations. For Na-like Ar a measurement was also performed over the Δn = 1 type of resonances. In the low-energy part of the Ar viii spectrum, enhancements of more than one order of magnitude are observed as compared to the calculated radiative recombination. The plasma recombination rate coefficients of the two Na-like ions are compared with calculated results from the literature. In the 10 3 −10 4 K range, large discrepancies are observed between calculated plasma rate coefficients and our data. At higher temperatures, above 10 5 K, in the case of both ions our data is 30% higher than two calculated plasma rate coefficients, other data from the literature having even lower values. Conclusions. Discrepancies below 10 4 K show that at such temperatures even state-of-the-art calculations yield plasma rate coefficients that have large uncertainties. The main reason for these uncertainties are the contributions from low-energy resonances, which are difficult to calculate accurately.

Electron-ion recombination of H- and He-like sulfur

Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombin ...

Recombination rate coefficients of Be-like neon

Aims. Merged-beam and plasma recombination rate coefficients for Be-likeNe vii were extracted from results of a merged-beam typeexperiment.Methods. The cryring heavy-ion storage ring was used to de ...

RECOMBINATION RATE COEFFICIENTS OF BORON-LIKE Ne

Recombination of Ne5+ was measured in a merged-beam type experiment at the heavy-ion storage ring CRYRING. In the collision energy range 0-110 eV resonances due to 2s(2)2p -> 2s2p(2) (Delta n=0) ...

Recombination and electron impact excitation rate coefficients for S XV AND S XVI

Recombination and electron impact excitation of S14+ and S15+ ions was measured at the Stockholm refrigerated electron beam ion trap. The collision energy range was 1.4-3 keV, where we covered the ...