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Recent experimental results in the Large Helical Device have indicated that a large pressure gradient can be formed beyond the stability criterion for the Mercier (high-n) mode. While the stability against an interchange mode is violated in the inward-shifted configuration due to an enhancement of the magnetic hill, the neoclassical transport and confinement of high-energy particle are, in contrast, improved by this inward shift. Mitigation of the unfavourable effects of MHD instability has led to a significant extension of the operational regime. Achievements of the stored energy of 1 MJ and the volume-averaged beta of 3% are representative results from this finding. A confinement enhancement factor above the international stellarator scaling ISS95 is also maintained around 1.5 towards a volume-averaged beta of 3%. Configuration studies on confinement and MHD characteristics emphasize the superiority of the inward-shifted geometry to other geometries. The emergence of coherent modes appears to be consistent with the linear ideal MHD theory; however, the inward-shifted configuration has reduced heat transport in spite of larger amplitude of magnetic fluctuation than the outward-shifted configuration. While neoclassical helical ripple transport becomes visible for the outward-shifted configuration in the collisionless regime, the inward-shifted configuration does not show any degradation of confinement deep in the collisionless regime (nu*<0.1). The distinguished characteristics observed in the inward-shifted configuration help in creating a new perspective of MHD stability and related transport in net current-free plasmas. The first result of the pellet launching at different locations is also reported.

Additional information

Authors: YAMADA H ET AL, National Institute for Fusion Science, Toki, Gifu (JP);ASHIKAWA N ET AL, Department of Fusion Science, School of Mathematical and Physical Science, Graduate University for Advanced Studies, Hayama (JP);BAYLOR L R, Oak Ridge National Laboratory, Oak Ridge (US);COOPER W A, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Federale de Lausanne (CH);NOTAKE T ET AL, Department of Energy Engineering and Science, Nagoya University (JP);REWOLDT G, Princeton Plasma Physics Laboratory, Princeton (US)
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion, 43 (December 2001), pp. A55-A71
Record Number: 200214718 / Last updated on: 2002-05-16
Original language: en
Available languages: en