INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS B: ATOMIC, MOLECULAR AND OPTICAL PHYSICS J. Phys. B: At. Mol. Opt. Phys. 36 (2003) 2019–2032 PII: S0953-4075(03)58862-9 Electron impact ionization of Kr XI–Kr XIX ions I Beigman 1 , P Defrance 2 and L Vainshtein 1 1 Lebedev Physical Institute, Leninsky Avenue, 53, 119991, Moscow, Russia 2 Department of Physics (FYAM) 2, Chemin du Cyclotron, B-1348 Louvain-la-Neuve, Belgium Received 26 November 2002, in final form 1 April 2003 Published 6 May 2003 Online at stacks.iop.org/JPhysB/36/2019 Abstract Cross sections for the single ionization of Kr XI–XIX ions by electron impact are calculated in the Coulomb–Born approximation by the code ‘ATOM’ and compared with experimental data and other theoretical results for Kr XI, Kr XII and Kr XIX. Single electron impact ionization is the sum of the contributions from direct ionization and from excitation of the autoionizing levels. The first part includes only ionization from the 3s, 3p and 3d shells since ionization from the 1s, 2s, 2p shells results in double ionization. The autoionizing levels (1s 2 2s2p 6 3s 2 3p 6 3d m nl and 1s 2 2s 2 2p 5 3s 2 3p 6 3d m nl ) decay via autoionization and finally contribute to single ionization. The results are found to be in satisfac- tory agreement with the experimental results obtained in a crossed electron–ion beam experiment in the energy range from threshold to about 6 keV. The case of ions formed in metastable states is studied as they wereobserved experimentally. 1. Introduction In the design of future thermonuclear reactors,krypton has been recognized as a good candidate for the spectroscopic diagnostics of, for instance, the temperature in the plasma edge, as well as in the central plasma. For this reason, a good knowledge of related spectroscopic and collisional atomic data is needed in order to interpret the observations of various plasma parameters (Janev 1993). Among the processes playing a role in this field, electron-impact ionization of atoms and ions is a fundamental one, because it governs the ion charge state distribution evolution in the plasma. As a consequence, the corresponding ionization cross sections are required for plasma modelling. For single ionization, experimental cross sections for Kr XI–XIX have been published. In particular, the largest charge states were studied in the laboratory of Louvain-la-Neuve for Kr XI, Kr XII (Oualim et al 1995) and Kr XIII–XIX (Khouilid et al 2001a) in the energy range from subthreshold to about 6 keV. In the experiment, the animated crossed-beams method is applied in an apparatus (Duponchelle et al 1995) specially designed to study electron-impact ionization (single and multiple) of multiply charged ions (X q+ ) up to q = 20. The krypton ions are extracted from an electron cyclotron resonance ion source (Baru´ e et al 1998) and are accelerated by a voltage of some kilovolts, mass-analysed, focused and deflected to the 0953-4075/03/102019+14$30.00 © 2003 IOP Publishing Ltd Printed in the UK 2019