2018 Impact factor 2.481
Hadrons and Nuclei
Eur. Phys. J. A 6, 471-477

Recoil separator ERNA: ion beam specifications

D. Rogalla1 - M. Aliotta1 - C.A. Barnes2 - L. Campajola3 - A. D'Onofrio4 - E. Fritz1 - L. Gialanella1 - U. Greife1 - G. Imbriani3 - A. Ordine3 - J. Ossmann1 - V. Roca3 - C. Rolfs1 - M. Romano3 - C. Sabbarese4 - D. Schürmann1 - F. Schümann1 - F. Strieder1 - S. Theis1 - F. Terrasi4 - H.P. Trautvetter1

1 Institut für Physik mit Ionenstrahlen, Ruhr-Universität Bochum, Bochum, Germany
2 California Institute of Technology, Pasadena, USA
3 Dipartimento di Scienze Fisiche, Universita Federico II, Napoli and INFN, Napoli, Italy
4 Dipartimento di Scienze Ambientali, Seconda Universita di Napoli, Caserta and INFN, Napoli, Italy

Received: 25 October 1999 Communicated by B. Povh

Abstract
For improved measurements of the key astrophysical reaction 12C( $\alpha,\gamma$)16O in inverted kinematics, a recoil separator ERNA is being developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with about 50% efficiency. Calculations of the ion beam optics including all filtering and focusing elements of ERNA are presented. Since the 12C projectiles and the 16O recoils have essentially the same momentum, and since the 12C ion beam emerging from the accelerator passes through a momentum filter (analysing magnet), the 12C ion beam must be as free as possible from 16O contamination for ERNA to succeed. In the present work, the 16O contamination was reduced from a level of $1 \times 10^{-11}$ to a level below $2 \times 10^{-29}$ by the installation of Wien filters both before and after the analysing magnet. The measurement of these and other beam specifications involved other parts of the final ERNA layout - sequentially a Wien filter, a $60^{\circ}$ dipole magnet, another Wien filter, and a $\Delta$E-E telescope. The setup led to a measured suppression factor of $5 \times 10^{-18}$ for the 12C ion beam. The experiments also indicate that an almost free choice of the charge state for the 16O recoils is possible in the separator.


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