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Abstract

Non-intrusive emission spectroscopy plasma diagnostics allows for evaluation of the local temperature and density; it also provides information on the constituents and the most important processes encountered in the plasma. For a satisfactory application of such diagnostics, a full Collisional- Radiative (C-R) model is needed, taking into account all the present species, both neutral and ionized, together with their excited states (including their structure and transition probabilities) and also the rates of the contributing processes. As a sequel of our emission spectroscopy studies we report here on work in progress on emission spectroscopy diagnostics of theWEGA Stellarator plasma, when fed with Argon. This device, operated at IPP Greifswald, is mainly used for basic research in plasma physics, including educational training and for testing of new diagnostic equipment [1]. Emission spectroscopy diagnostics will be subsequently extended to He discharges, which are also studied in the same device. The present task takes advantage of a general study aiming for the characterization and optimization of the WEGA plasmas [2] and of bolometric results obtained recently [3]. According to measurements made at IPP, an electron temperature Te of about 10 eV prevails in WEGA for Ar discharges, with an electron density ne of about 1012 cm−3. Our calculations, based on a simple coronal model, are applied to the full Ar I to Ar V spectra, plus partial radiation from Ar5+. Of course, all of these spectra are not expected to be simultaneously present in an homogeneous plasma with a single Te, but in the case of the separatrix- and/or limiter-plasmas of WEGA a “mixture of temperatures” may explain the detection of signatures of all of the ionized Ar species as well as of the neutral, possibly altering the total radiated energy. Accordingly, more than one Maxwellian distribution prevails for some or for all of the present species. Typical Ar I-III spectral lines have now been identified in various WEGA discharges. The main features of the relevant spectra will be shown and commented on during the Conference. They will also be compared to our theoretical spectra, in order to investigate the real presence and percentage of each ionized species and judge about the form of Te in connection with possible departures from the unique Maxwellian distribution.