We study the excitation of parabolic Stark states in hydrogen atoms by collisions with fast ions. It is shown that excitation cross sections are very sensitive to the angle between the electric field and the projectile velocity. The calculated collisional data are implemented in a newly developed collisional–radiative model involving parabolic quantum states of hydrogen. Our simulations are shown to explain the frequently observed non-statistical behaviour of the Hα component intensities under typical conditions of a motional Stark effect (MSE). A good agreement with the MSE data from the Joint European Torus (JET) for emission of the σ and π components (Mandl et al 1993 Plasma Phys. Control Fusion 35 1373) is obtained for the first time.

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The measured K α spectra of He-like argon were used to determine the densities of H-, He-and Li-like argon ions in ohmically heated plasmas in the tokamak TEXTOR. The obtained ratio of the densities for the Li-and He-like ions shows a significant deviation from coronal equilibrium. In order to interpret these results numerical modelling of the impurity transport was performed by the code RITM with neoclassical and anomalous contributions to the transport coefficients. The measurements show that the transport in the plasma core is much higher than that predicted from the model and has a strong correlation with the line averaged density. This paper also demonstrates the unique ability of the He-like spectra to separate the transport properties and the charge-exchange processes in the plasma.