Spectroscopic measurements of the D α and H α line profiles emitted within the edge region of a tokamak plasma, have revealed the existence of a cold central component, broadened mainly by the Zeeman effect arising from the confining magnetic field. Evaluation of the Doppler broadening suggests that the cold component is probably produced by electron impact-induced molecular dissociation, dissociative excitation being one of the few mechanisms which can explain the formation of atoms of kinetic energy around 0.2 eV against a background of comparatively hot electrons and ions. Further analysis of these line profiles, observed along different directions in the equatorial plane and under various tokamak discharge conditions, reveals, in addition to this effective 'cold temperature', an effective 'lukewarm temperature', which we explain in terms of an appreciable collisional heating mechanism. Estimates of the rates for ion-induced dipole and ioninduced quadrupole collisions with excited atoms, yield values of the correct order of magnitude for this observed 'lukewarm temperature'. In addition, measurements of Balmer-α line profiles, radiated from a gas discharge in a magnetic field of similar magnitude, are analysed and their shapes compared with those from the tokamak plasma.

Profiles of the Balmer lines D,(H,), Db(Hs) and D, (H,) have been measured in the scrape-off layer and within the edge of the TEXTOR (upgrade) plasma, under Ohmic conditions and with neutral-beam injection. Each line profile shows a strong Zeeman effect in the vicinity of line centre, and a marked central dip when mainly the ( I components are observed. The line core evidently originates from cold atoms in the edge plasma, excited in the course of molecular dissociation, while the broad pedestal on which the core rests is radiated by excited atoms produced through chargeexchange recombination of deuterons (protons), transported outwards from the much hotter plasma interior, and by atoms heated directly by collisions with the deuterons (protons). Core temperatures of about 0.5 eV and less are obtained from line profile analysis.

Spectroscopic measurements of low‐n Balmer line profiles of atomic hydrogen and deuterium, emitted within the edge region of the TEXTOR‐94 tokamak plasma, have revealed the existence of a class of cold excited atoms, whose probable origin has been ascribed to electron impact‐induced molecular dissociation. Associated with these cold radiators are a second group of ‘lukewarm’ atoms, i.e. atoms heated by elastic collisions with hot protons (deuterons) diffusing outward from the plasma interior, as well as a third group of ‘hot’ atoms, produced in the corresponding excited states directly by charge‐exchange recombination between protons (deuterons) and boundary region atoms. A mechanism recently proposed to explain the heating process quantitatively, in terms of elastic atom‐ion collisions, is applied and discussed in this paper.

Experimental results from TEXTOR are presented to provide strong evidence for the feasibility of the "cold radiative plasma mantle", a concept which might be a possible solution for the energy exhaust problem in a fusion reactor. The concept is compared with the high density divertor. The compatibility to other constraints, limitations and open problems are discussed, in particular the issues of stationarity (feed-back control, thermal instabilities, q=2), energy confinement. Heexhaust and fuel dilution.

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.

The injection of 10-100 keV Lio diagnostic beams into magnetically confined fusion plasmas causes collisionally induced Lil emission at 670.8 nm, in close relation to the edge plasma electron dcnsity. A numcrical method Cor quantitative reConstruction of the plasma density exclusively from rclaliw Lil 670.8 nm emission profilcs as measured slang the diagnostic beam has been developed, involving all relevant collisional interactions of the Li atoms with plasma constituents. The applicahility of the descrihed algorithm is illustrated by experimental results obtained for the TEXTOR Tokamak edge plasma at KFA Jirlich.

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Plasma-wali interaction and impurity transport processes in the outermost region of magnetically confined hot plasmas (the so-called plasma edge) must be well understood for successful development of future thermonuclear fusion reactors. To this goal, sufficiently detailed edge plasma diagnostics are in great demand. By injecting a fast Li beam into the edge plasma region, a great number of information can be obtained with excellent space and time resolution. This so-called Li-beam plasma spectroscopy gives access not only to edge plasma density profiles from the collisionally excited Li atoms, but also to the impurity concentration and temperature profiles via line emission induced by electron capture from the injected Li atoms by the impurity ions. Full utilization of all capabilities requires a reliable data base for the atomic collision processes involving injected Li atoms and plasma constituents (i.e., electrons, hydrogen ions, and relevant impurities in their various charge states), since a precise modeling of Li beam attenuation and excited-state composition has to be made for evaluating desired plasma properties from the related spectroscopical measurements. The most recent methodical improvement permits a fully consistent determination of absolute edge plasma density profiles by measuring only relative LiI line emission profiles. This is of special interest for investigating rapid edge plasma density fluctuations in connection with, e.g., ELMS, L-H mode transition, turbulence or edge cooling by impurity injection. This paper describes the capabilities of Li-beam edge plasma spectroscopy by way of illustrative examples from measurements at the tokamak experiment TEXTOR.