Recombination in Electron Coolers

An introduction to electron}ion recombination processes is given and recent measurements are described as examples, focusing on low collision energies. Discussed in particular are "ne-structure-mediated dielectronic recombination of #uorine-like ions, the moderate recombination enhancement by factors of typically 1.5}4 found for most ion species at relative electron}ion energies below about 10 meV, and the much larger enhancement occurring for speci"c highly charged ions of complex electronic structure, apparently caused by low-energy dielectronic recombination resonances. Recent experiments revealing dielectronic resonances with very large natural width are also described. 2000 Elsevier Science B.V. All rights reserved

Hochaufloesende Messung zur dielektronischen Rekombination von metastabilen und Grundzustands-Li"+-Ionen

At the heavy ion storage ring TSR dielectronic recombination of Li"+-ions in both configurations (1s"2) 1"1S (ground-state) and (1s2s) 2"3S (K-vacancy-configuration; metastable state with a lifetime of about 50 s) was measured with high resolution. The electron impact excitations #DELTA#n = 1 and #DELTA#n = 0 on these systems lead to formation of doubly excited states (resonances) in the continuum of neutral Li which can be observed through their radiative de-excitation into stable states of Li. The energy of the Li"+-beam was 13.3 MeV, which corresponds to an electron energy of about 1 keV in the laboratory frame. The spectroscopical investigation of recombination spectra of these systems was carried out by merging the electron with the ion beam and by varying the electron energy. The #DELTA#n = 0 excitation was recorded at center-of-mass energies between 0 and 4 eV, the #DELTA#n = 1 resonances between 52 and 65 eV. The resulting high resolution spectra allow a much better comparison with the theory than the previous measurements. In light ions the electron-electron interaction is stronger compared to the electron-nucleus-interaction. Therefore the calculation of DR in such ions is more difficult. In the same experiment we were also able to measure the lifetime of the 2 "3S_1-state in Li"+, which decays via a forbidden M1-transition. The result shows a better accuracy than the only experiment carried out previously. (orig.)SIGLEAvailable from TIB Hannover: RO 6920(1999,21) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Recent dielectronic recombination experiments

New recombination experiments with merged cold beams of electrons and atomic ions have been carried out at the storage ring facilities TSR in Heidelberg, ESR in Darmstadt, and CRYRING in Stockholm. A brief overview is given on the recent activities in which the Giessen group was engaged. Topics of this research were dielectronic recombination (DR) of astrophysically relevant ions, recombination of highly charged ions with respect to cooling losses in storage rings, field effects on DR, search for interference effects in photorecombination of ions, correlation effects in DR of low-Z ions, spectroscopy of high-Z ions by DR, and lifetimes of metastable states deduced from DR experiments

Storage ring at HIE-ISOLDE: technical design report

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report

Physics book: CRYRING@ESR

The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002)