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Enhanced radiative recombination of U⁹²⁺ ions with cooling electrons for the K-shell

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Enhanced radiative recombination of U

92+

ions

with cooling electrons for the K-shell

D. Bana´s1, H. F. Beyer2, F. Bosch2, C. Brandau2, S. B¨ohm5, S. Chatterjee2, M. Czarnota1, J.-Cl. Dousse6, A. Gumberidze2,3, S. Hagmann2, C. Kozhuharov2,

D. Liesen2, P. H. Mokler2, A. M¨uller5, A. Kumar2, M. Pajek1, R. Reuschl2, E. W. Schmidt5, D. Sierpowski7, U. Spillmann2, A. Surzhykov4, Th. St¨ohlker2,4,

J. Szlachetko1,6, S. Tashenov2, S. Trotsenko2, P. Verma2, and A. Warczak7

1Institute of Physics, Jan Kochanowski University, 25-406 Kielce, Poland 2GSI Helmholtzzentrum f¨ur Schwerionenforschung, D-64291 Darmstadt, Germany

3Extreme Matter Institute, D-64291 Darmstadt, Germany

4Physikalisches Institut der Universit¨at Heidelberg, D-69117 Heidelberg, Germany 5Institut f¨ur Kernphysik, Justus-Liebig Universit¨at, D-35392 Giessen, Germany 6Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland

7Institute of Physics, Jagiellonian University, 31-007 Cracow, Poland

Synopsis Observed enhancement of K-shell radiative recombination (RR) of bare uranium ions with cooling

electrons is interpreted in terms of of distant transverse collisions in magnetized electron-cooler plasma described within the semiclassical geometrical model (SGM), which was recently proposed. The Monte Carlo simulations based on the proposed approach explains the enhancement measured in RR of U92+ions with cooling electrons for the K-shell.

Recently we have proposed [1] new interpre-tation of the RR enhancement using the de-veloped semiclassical geometrical model (SGM) which adopts the standard quantum mechanical RR cross sections to introduce a simplified con-cept of fully ”absorbing” RR sphere. Within this model we demonstrate that the enhancement of the RR is caused by ”transverse’ collisions with impact parameters in the μm range, with cut-off value depending on a strength of the guiding B-field in the electron cooler.

The proposed SGM model reproduces the scaling of the RR excess rates observed at exper-iments at the TSR [2] and, moreover, predicts strong enhancement for low n-states, which was observed in our x-ray experiment on RR for the K-shell [3]. It should be noted that for stronger magnetic fields this model predicts linear depen-dence on the B-field, i.e. Δα ∝ B, which was suggested in earlier experiment at the GSI [4] (see Fig. 1). For a better description of the RR en-hancement we have performed the Monte Carlo simulations based on the SGM approach which predicts more realistic B-field dependence and impact parameter cuf-off. It is important to note, that the absolute value of the RR enhancement predicted by the SGM is close to the observed one for the K-shell [3]. Additionally, the Monte Carlo simulations involving the angular distributions of x-rays demonstrate that the proposed approach describes well the RR enhancement measured in x-ray experiment on recombination of U92+ ions with cooling electrons.

This work was supported by the Polish Min-istry of Science and Higher Education under Grant No. N N202 463539. 10 1 10 2 10 3 10 4 1E-15 1E-14 1E-13 1E-12 T =120meV T || =0.1meV b max =1 m N=10 8 B(mT) n=1 Z=92

Figure 1. The B-field dependence of the excess

of the total RR rate in the magnetized electron cooler as obtained using the Monte-Carlo simula-tions based on the SGM model.

References

[1] Bana´s D et al. 2010 15th Int. Conf. on the Phys. of Highly Charged Ions, Shanghai, China, A-b38. [2] Gwinner G et al. 2000 Phys. Rev. Lett. 84 4822. [3] Bana´s D et al. 2009 Eur. Phys. J. ST169 15-18. [4] Shi W et al. 2001 Eur. Phys. J. D15 145. 1E-mail:d.banas@ujk.kielce.pl

 Published in "-RXUQDORI3K\VLFV&RQIHUHQFH6HULHV  " which should be cited to refer to this work.

Figure

Figure 1. The B-field dependence of the excess of the total RR rate in the magnetized electron cooler as obtained using the Monte-Carlo  simula-tions based on the SGM model.

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