This paper shows the extensions of the authors' previous work on absolute cross sections for electron capture into He+ (4l) states, produced in collisions of He2+ with atomic and molecular hydrogen, to higher impact energies (27-132 keV amu-1) than used before (2-13 keV amu-1). The cross sections have been deduced from photon emission profile measurements along the ion beam axis, detecting the He II(n=4 to n=3) radiation at a wavelength of 4686 AA. The results for collisions with atomic hydrogen generally show reasonable agreement with the atomic orbital calculations of Fritsch (1989) below 50 keV amu-1 and at the highest impact energies used (E>or=100 keV amu-1) approach the data of the distorted wave approximation by Belkic et al. (1990).

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We have determined absolute cross sections for electron capture into the quasi-degenerate SZ states of Be + produced in collisions of He 2+ on atomic hydrogen. The cross sections have been deduced by deconvoluting spatial HeII(n = ~ -9 n = 3) emission profiles. The measurements have been performed in the impact energy range of 2 -130 keV/amu. The results are compared with theory. In addition we discuss the relevance of these cross sections t o ~-particle diagnostics in fusion plasmas. At the JET tokamak the HeII(n = 4 -9 n = 3) emission can be used to determine related quantities like ion temperature, plasma rotation and local =-particle densities. I. Charge exehsnge cross sectionsIn several publications (e.g.[I-4]) we have reported on our Photon Emission Spectroscopy experiments of electron capture into excited states in collisions of bare ions with atomic hydrogen, which are highly relevant for the diagnostics of fusion plasmas [5,6]. Here we shall confine ourselves to the processfollowed by HeII(n = $ -~ n = 3) photon emission at 468.6 nm. To produce He 2+ ion beams in the energy ranges of 2 -13 and 25 -130 keV/amu two accelerators have been used, the ECR ion source installed at the KVI (Groningen) and the Van de Graaff accelerator at AMOLF (Amsterdam) respectively. In the latter case He 2+ arises from stripping the primary accellerated Be + beam. In a collision chamber the ion beam crosses a partly dissociated hydrogen beam effusing from a radio frequency discharge source. The photon emission is observed with a monochromator (see e.g. [I-4]).The ~Z state selective capture cross sections have been determined from the HeII(n = $ -. n = 3) emission, measured along the ion beam axis, by means of deconvolution technique [2,3,4], which exploits the fact that the lifetimes of the 4Z states are different.The results for the HeII(,= 4 -9 ~ = 3) are given in fig. 1