S. Asp

DENSITY DEPENDENCE OF RECOMBINATION IN THE ELECTRON COOLER OF CRYRING

The electron-ion recombination rates of Ne10+ and D+ have been measured as a function of relative energy and electron density. We found a strong enhancement of e-Ne10+ recombination over expected radiative recombination rates below 1 meV relative energies, reaching a factor of 4 close to zero relative energy. Remarkably, the measured rate coefficients decrease as a function of electron density for both systems. Studies of recombination of D+ indicate that this density dependence may be due to temperature variations of the electron beam with the electron density.

Laser-Induced Recombination of D(+)

Laser induced recombination into the L shell (n = 2) of deuterium was investigated at the heavy-ion cooler storage ring CRYRING for two values of the electron density. The data shows the expected enhancement of radiative recombination, induced by the intense laser field applied, over the spontaneous case. Like in previous measurements, a strong intensity below the photoionization threshold was observed. Qualitatively, this gain is described by an average field induced threshold shift model. However, when reducing the electron density by roughly a factor of two, the effective field increased by an order of magnitude. This surprising result indicates that the precise origin of the observed fields is not simply related to the known field sources.

DIELECTRONIC RECOMBINATION OF LI-LIKE NEON AND ARGON

We have measured dielectronic recombination rates and energies for δn=0 transitions of Ne7+ and Ar15+ beams stored in CRYRING. The energy resolution was in the order of 10−2 eV FWHM; the absolute accuracy in the position of the resonances is in the same order. The energy positions of the dielectronic recombination resonances are compared to theoretical calculations of the fine-structure splittings.

Study of radiative recombination into deuterium Rydberg states

Deuterium Rydberg states which were populated by radiative recombination in the electron cooler of CRYRING have been detected using state-selective field ionization in an external electric field. Absolute radiative recombination rate coefficients for Rydberg states between 12<or=n<or=18 are extracted and agree well with theoretical calculations using the Kramers cross section corrected by the Gaunt factor. The influence of the Stark effect on the Rydberg states has to be taken into account to explain the data. It was found that the relative population distribution of Rydberg states as well as the rate coefficient are very sensitive to the transverse electron temperature in the electron cooler.

Using an OPO laser system for recombination studies in a storage ring: LIR to n=3 states of deuterium

We have investigated the use of a one-stage optical parametric oscillator (OPO) laser system for studies of laser induced radiative recombination (LIR) of stored ions. For the test case considered, LIR into n = 3 states of deuterium, we find that the energy resolution is limited by the broad linewidth of the OPO. Within this resolution, our LIR results are in good agreement with a theoretical average field induced threshold shift model.

Observation of Δn=1 dielectronic recombination resonances of boronlike argon

We report here an observation ofδn=1 dielectronic recombination resonances of boron-like argon in the energy region 140–195 eV. With the coolers electron beam as a target, a resolution of approximately 0.6 eV FWHM was obtained in the observed energy range. The energies of the doubly excited states were estimated with a Hartree-Fock calculation, which indicates that the observed resonances are from Ar13+(1s22s22p) to Ar12+(1s22s23l3l′) and Ar12+(1s22s2p3l3l′) transitions.

DIELECTRONIC RECOMBINATION OF AR13+ AT CRYRING

We have investigated Δn = 0 dielectronic recombination resonances of Ar13+ at CRYRING. The Ar13+ ions were obtained from the electron beam ion source CRYSIS. The ultracold electron beam produced in the modified electron cooler was used as the electron target, resulting in resonance widths less than 30 meV FWHM. Determination of the observed resonance line energies, which requires transformation from laboratory to center of mass frame, includes acceleration of the ion beam due to the drag force encountered as the electron energy is scanned. With this transformation the uncertainty in absolute line positions has been reduced to less than 30 meV.

Low energy electron-ion recombination experiments at CRYRING

Results from recent experiments at the heavy-ion synchrotron storage ring CRYRING are described. These experiments include radiative recombination of deuterons using several separate techniques to investigate specific n-level capture, and dielectronic recombination of He+ and Ar13+. New methods applied to the argon dielectronic recombination experiment provided an energy resolution better than 30 meV FWHM and a determination of the peak positions to ±30 meV.

Electron-ion recombination using the modified cryring electron cooler

Abstract Recent electron-ion recombination experiments at the heavy-ion syncrotron storage ring CRYRING are described. These experiments include state selective radiative recombination into mid-n levels of deuterons and dielectronic recombination of Ar13+. Modifications to the CRYRING electron cooler have reduced the transverse electron temperature to a few tenths of an meV/kB. The ultrahigh energy resolution achieved is demonstrated in the recent experiments. The widths of the Ar13+ Δn = 0 dielectronic recombination resonances are resolved to 30 meV FWHM. Detailed calculation of the electron-ion interaction energies has allowed a determination of the peak positions to ± 30 meV.