Anisotropic distributions of suprathermal particles were investigated by the multidirectional passive neutral particle diagnostic [1, 2]. Time and angle resolved measurements of f(v,θ,t) were made in experiments with tangential H NBI into multi-ion-species target plasmas. The formation of the flux of neutral atoms from a quasistationary plasma column and the attenuation of this flux on the way out to the periphery are determined by the three groups of elementary atomic processes, viz. charge exchange, recombination and ionization. The charge exchange process is of primal importance for calculating both the local source function of atoms in the plasma and the loss of atoms along the observation direction. H⁺ charge exchange on He⁰ and He⁺ needs to be taken into account in case of hydrogen NBI-heated helium target plasma. In studies of high-energy proton distributions in multi-species plasmas including Ne and Ar components the charge capture cross-sections by protons from the atoms and various ions of these noble gases are required: H⁺+Ne^k+→H⁰+Ne^(k+1)+ and H⁺+Ar^l+→H⁰+Ar^(l+1)+. The experimental data on these cross-sections is not abundant. In [3, 4] a numerical code was described for calculating the distribution of various possible charge exchange targets in a multi-species plasma. Various theoretical estimations of cross-sections exist such as the one suggested by Oppenheimer (1928) and Brinkman and Kramers (1930) based on the first-order quantum perturbation theory. This so-called OBK approximation allows to obtain an analytic expression for the charge transfer probability amplitude. When fast ion distributions are of interest, it is enough to know the high energy asymptotic behaviour of the charge exchange cross-sections for <σv>-correction of the neutral particle energy spectra.

References