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Abstract

The ITER neutral beam injection is based on the acceleration and neutralization of negative deuterium ions. The target performance for the ITER beam source is to accelerate to 1 MeV a 40 A D{-} beam, with a current density of 200 A m{-2}, with pulse lengths of up to 1000 s. It was found that in long pulse operation the negative ion yield from the filamented Kamaboko III ion source (a model of ITER ion source) degrades in comparison with short pulse operation, <5 s. This could be linked to the behaviour of caesium (Cs), which is added to the source to increase its negative ion yield and tungsten (W) evaporated from filaments. Cs and W are co-adsorbed on the source walls and the plasma grid and the composition of this coating can vary during long pulse operation. The possible consequences of this changing surface on the negative ion production will be discussed.
Tungsten filaments have a limited lifetime in the ion source and changing filaments and refilling of the Cs oven are the only scheduled maintenance events for the ITER injectors. These are complicated operations as the ITER injectors will be highly activated and all maintenance has to be carried out remotely. Therefore, increasing the filament lifetime and decreasing the Cs consumption are highly desirable. This paper presents results of relative measurements (including spectroscopic and chemical) of the W content of the Kamaboko-III source and reports relevant calculations on Cs consumption and W evaporation.

Additional information

Authors: KRYLOV A, RRC 'Kurchatov Institute', Moscow (RU);BOILSON D, Association EURATOM-DCU, PRL/NCPST, Dublin (IE);FANTZ U, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);HEMSWORTH R S, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);PROVITINA O, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);PONTREMOLI S, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);ZANIOL B, Associazione Euratom-ENEA sulla Fusione, Consorzio RFX, Padova (IT)
Bibliographic Reference: An article published in: Nuclear Fusion 46 (2006), pp. S324-S331
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/10.1088/0029-5515/46/6/S14
Record Number: 200719114 / Last updated on: 2007-04-11
Category: PUBLICATION
Original language: en
Available languages: en