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Abstract

A numerical and experimental study of the impurity concentration and radiation in the EXTRAP-T2R device is reported. The experimental setup consists of an 8-chord bolometer system providing the plasma radiated power and a vacuum-ultraviolet spectrometer providing information on the plasma impurity content. The plasma emissivity profile as measured by the bolometric system is peaked in the plasma centre. A one dimensional Onion Skin Collisional-Radiative model (OSCR) has been developed to compute the density and radiation distributions of the main impurities. The observed centrally peaked emissivity profile can be reproduced by OSCR simulations only if finite particle confinement time and charge-exchange processes between plasma impurities and neutral hydrogen are taken into account. The neutral hydrogen density profile is computed with a recycling code. Simulations show that recycling on metal first wall such as in EXTRAP-T2R (stainless steel vacuum vessel and molybdenum limiters) is compatible with a rather high neutral hydrogen density in the plasma centre. Assuming an impurity concentration of 10% for oxygen and 3% for carbon compared with the electron density, the OSCR calculation including lines and continuum emission reproduces about 60% of the total radiated power with a similarly centrally peaked emissivity profile. The centrally peaked emissivity profile is due to low ionisation stages and strongly radiating species in the plasma core, mainly O4+ (Be-like) and C(3+) Li-like.

Additional information

Authors: CORRE Y, KTH-Physics Department Alba Nova, Association EURATOM-VR, Stockholm (SE);RACHLEW E, KTH-Physics Department Alba Nova, Association EURATOM-VR, Stockholm (SE);GRAVESTIJN R M, KTH-Physics Department Alba Nova, Association EURATOM-VR, Stockholm (SE);HEDQVIST A, KTH-Physics Department Alba Nova, Association EURATOM-VR, Stockholm (SE);CECCONELLO M, KTH-Physics Department Alba Nova, Association EURATOM-VR, Stockholm (SE);PÉGOURIÉ B, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);SCHUNKE B, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);STANCALIE V, Association EURATOM-MEC, NIL, Plasma and Radiation Physics, Bucharest (RO)
Bibliographic Reference: An article published in: Physica Scripta 71 (2005), pp. 523-531
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/10.1238/Physica.Regular.071a00523
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