Doppler Broadening and Magnetic Field Effects on Some Ion Impurity Spectra Emitted in the Boundary Layer of a Tokamak Plasma

Abstract

Examples are presented of Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: CII, CIII, CIV, Sin, and Sim. The shapes of these spectral lines are significantly influenced by the confining magnetic field of some 2T, in some cases exhibiting an appreciable Paschen-Back effect which complicates their appearance. It is shown that reliable values for the particular ion temperature can be obtained from the Doppler widths of the various Zeeman components, when the presence of the magnetic field is properly accounted for. Such temperatures derived from partially ionised impurity species should, however, be cautiously interpreted, as the ions in question probably do not exist for long enough in the particular ionisation stage to achieve thermal equilibrium with the background deuterons and protons. This interpretation of our results is supported by a simple one-dimensional model of ionisation and collisional heating processes in the plasma boundary.

Spectroscopic Studies of Cold Atomic Hydrogen and Deuterium Produced in a Tokamak Edge Plasma

“…[47] (see also [34]). While the order-of-magnitude agreement clearly serves well to substantiate the present model, there are apparent discrepancies, which can plausibly be explained by considering, e.g., the lack of good spatial resolution of the measurements [34], [36], [47]. 6 -9 of [47]).…”

“…The choice in [21] of 0.25 eV as the Franck-Condon energy of the cold atoms [9] represented a significant departure from the earlier choice of 2 eV as the mean energy of the slow atoms [22]. This proved very convenient for the observation of not only charge-exchange spectra for ion temperature measurements [33], but also the spectra of species in low charge states [34], [35], which do not normally achieve equipartition with their environment [34], [37]- [39]. In that case, Doppler and instrumental broadening should be known to predominate [23], if one wishes to avoid detailed calculations.…”

“…As in the work just discussed, selection by linear polarizer of a single Zeeman component is often not possible, and one has to work instead with a set of closely-spaced Zeeman components of the same type. Since the σ ± components are completely dominant for this optical arrangement, the use of a linear polarizer (with quarter-wave plate) offers no particular advantage [34] in most cases, especially not for lines from highly excited hydrogenic ions, where the number of Zeeman components may be large [33] with or without elimination of one of the polarization states. Convenient exceptions are singlet transitions in LS-coupled atoms, e.g.…”

Charge exchange recombination spectroscopy on a diagnostic hydrogen beam—measuring impurity rotation and radial electric field at the tokamak TEXTOR

“…Corrections regarding finite slit height [29] , Zeeman effect and Fine-structure are applied [2,21,22] during the analysis process and thus accounted for regarding the resulting temperatures and velocities. Corrections regarding CXRS cross-sections are negligible due to the low temperatures and perpendicular viewing angle [43].…”

Spectroscopic measurements of impurity temperatures and parallel ion flows in the DIII-D divertor

“…Because ion temperatures in the divertor are usually less than 20 eV, it is necessary to account accurately for the nonlinear splitting of the sublevels of excited electronic states in a magnetic field (ZeemanPaschen-Back effect) when determining the Doppler widths [3,8]. Of all the transitions utilized for temperature measurements, deviations from a linear dependence on the field (Zeeman effect) appear most markedly in the B II multiplet, although they are evident in the other multiplets.…”