Influence of charge-exchange processes on x-ray spectra in TEXTOR tokamak plasmas: experimental and theoretical investigation

Abstract

Time-resolved high-resolution soft x-ray spectra from gas-puff injected Ar impurity ions have been investigated for neutral beam heated and ohmically heated discharges in the TEXTOR tokamak. The experimental spectra show systematic deviations from corona model calculations for the line intensities of the forbidden He-like lines x, y, z and the Li-and Be-like dielectronic satellite spectra: theoretical corona model calculations predict intensities significantly too low. High-intensity Li-like inner-shell excited satellites correlate with the neutral beam injection. The discrepancies could also be observed in the stationary phase of an inductively heated discharge. In the heating phase the discrepancies are even larger. We propose charge-exchange processes between the neutral atoms and the impurity ions as an explanation of the experimental findings. Good agreement with the experimental observations can then be obtained without the need for invoking large (anomalous) diffusion coefficients. A self-consistent coupling of the population kinetics of the neutrals and the impurity ions, also taking into account charge-exchange processes from excited states of hydrogen/deuterium permit the determination of the neutral fraction and of the electron lifetime on the sole basis of impurity spectra analysis. Independent Monte Carlo simulations of neutral gas transport also provides the ionization degree in the centre and the electron lifetime. These calculations are also in good agreement with the spectroscopic results.

Energy levels, radiative rates and electron impact excitation rates for transitions in Be-like Ti XIX

“…Emission lines of Li-like ions have been observed in the spectra of a variety of astrophysical [1]- [2] and laboratory plasmas [3]- [4]. Similarly, high gain lengths have been measured in lasing plasmas, particularly for the 3d-4f transitions of Al XI and Si XII [5] in the soft x-ray region.…”

Spectral Line Shapes as a Diagnostic Tool in Magnetic Fusion

“…In fact, a self-consistent analysis of the particle transport and charge exchange (including also charge exchange from excited states) with a self-consistent multilevel collisional-radiative approach has shown that charge exchange phenomena, particle transport and atomic data are very closely related, as proved for the argon spectra in Ref. [33].…”

Neutral helium line emission for edge plasma conditions

“…At present, o/ot = 0 is assumed and the system Eq. (1) is closed by normalization conditions (for more details see [10,11]):…”