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The research on diverters for stellarators is at the beginning. Extensive studies are being prepared on large helical device (LHD) and W7-X. W7-AS is now being operated with an open island diverter (ID), which serves as a test bed for the W7-X diverter. The diverter enables access to a new NBI-heated, high-density operating regime with improved confinement properties. This regime-the high-density H-mode (HDH)-displays no evident mode activity, is extant above a threshold density and characterized by flat density profiles, high-energy- and low-impurity-confinement times and edge-localized radiation. Impurity accumulation, normally associated with ELM-free H-modes, is avoided. Quasi-steady-state discharges with n(e) up to 4×1E20 m{-3}, edge radiation levels up to 90% and plasma partial detachment at the diverter targets can be simultaneously realized. The accessibility to other improved confinement modes in W7-AS (conventional H-mode and OC-mode) is not restricted by the diverter. The results provide a promising basis for future experiments, in particular on W7-X, and recommend the ID as a serious candidate for solving the plasma exhaust problem in stellarators.

Additional information

Authors: MASUZAKI S, National Institute for Fusion Science, Toki-shii, Gifu-ken (JP);GRIGULL P ET AL, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE)
Bibliographic Reference: An article published in: Fusion Engineering & Design. 66-8:49-58, 2003 Sep.
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Record Number: 200417444 / Last updated on: 2004-03-15
Original language: en
Available languages: en
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