EGAS41 - Swansea University

41 st EGAS CP 5 Gdańsk 2009
Enhancement of radiative recombination of U 92+ ions with
cooling electrons for the lowest n=1 and n=2 states
D. Banaś 1,∗ , M. Pajek 1 , Th. Stöhlker 2,3 , H.F. Beyer 2 , F. Bosch 2 , C. Brandau 2,4 ,
S. Böhm 4 , S. Chatterjee 2 , M. Czarnota 1 , J.-Cl. Dousse 5 , A. Gumberidze 2 ,
S. Hagmann 2 , C. Kozhuharov 2 , D. Liesen 2 , P.H. Mokler 2 , A. Müller 4 , A. Kumar 2 ,
R. Reuschl 2 , E.W. Schmidt 4 , D. Sierpowski 6 , U. Spillmann 2 , S. Surzhykov 3 ,
J. Szlachetko 1,5 , S. Tashenov 2 , S. Trotsenko 2 , P. Verma 2 , A. Warczak 6
1 Institute of Physics, Jan Kochanowski University, Kielce, Poland
2 Gesellschaft für Schwerionenforschung, Darmstadt, Germany
3 Physikalisches Institut der Universität Heidelberg, Heidelberg, Germany
4 Institut für Kernphysik, Justus-Liebig Universität, Giessen, Germany
5 Department of Physics, University of Fribourg, Switzerland
6 Institute of Physics, Jagellonian University, Cracow, Poland
∗ Corresponding author: d.banas@ujk.kielce.pl,
The enhancement observed in experiments on radiative recombination (RR) of bare ions
with cooling electrons in ion storage/cooler rings [1,2,3] have attracted a wide interest
in last years to interpret this effect theoretically [4,5]. More precisely, these experiments
have shown that the radiative recombination rates, measured by detecting the recombined
ions, agree with the theoretical predictions for relative electron energies higher than the
transverse electron beam temperature T ⊥ , while for the lower electron energies an increase,
called the enhancement, of the measured rates with respect to the RR prediction
is observed, which saturates below the longitudinal electron beam temperature T ‖ . It was
found [1] that the excess of the recombination rate depends on the magnetic guiding field
in the electron cooler, however, the existing interpretations [4,5] of the enhancement effect
do not fully explain these observations.
In order to investigate the enhancement effect in more details, the state-selective x-ray
radiative recombination experiment has been performed in the electron cooler of the ESR
storage ring with decelerated bare U 92+ ions of energy 23 MeV/amu recombining with
electrons having relative energies in the range 0-1000 meV [6]. In this experiment the
x-ray K-RR and L-RR photons emitted from direct radiative recombination into the K-
and L-shells were measured in coincidence with recombined U 91+ ions both for on- and
and off-cooling electron energies. In this way, by comparing the measured K-RR and
L-RR rates with fully relativistic RR calculations [7] reproducing the data for off-cooling
electron energies quite well, the enhancement of RR for the n=1 and n=2 states was
derived for the cooling condition. The importance of the present results for interpretation
of the enhancement effect will be discussed in details.
Acknowledgment
The financial support of the Grant No. N20215931/3048 of the Polish MNiSW is kindly acknowledged.
References
[1] G. Gwinner et al., Phys. Rev. Lett., 84 4822 (2000)
[2] A. Hoffknecht et al., Phys. Rev. A 63 012702 (2000)
[3] W. Shi et al., Eur. Phys. J. D 15 145 (2001)
[4] C. Heerlein et al., Phys. Rev. Lett. 89 083202 (2002)
[5] M. Hörndl et al., Phys. Rev. Lett. 95 243201 (2005)
[6] D. Banaś, et al., Eur. Phys. J. ST 169 15 (2009)
[7] A. Surzhykov et al., Comput. Phys. Commun. 165 139 (2005)
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