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Abstract

Neoclassical tearing modes (NTMs) are studied in the ASDEX Upgrade tokamak [O. Gruber, H.-S. Bosch, S. G³nter et at., Nucl. Fusion 39, 1321 (1999)]. The onset beta(?) for NTMs scales with the normalized ion gyroradius rho{star}, independent of the normalized collisionality nu{star} for a wide range of nu{star}.This scaling is in accordance with both polarization current and X(perpendicular) over X(parallel) model, if for the latter, the heat flux limit on parallel heat conductivity is taken into account. Analysis of NTM stabilization experiments indicates that the typical seed island size is 1-1.5 cm, again in agreement with both models. Mode coupling to the q = 1 surface is a crucial element in determining the impact of the NTM on the discharge performance. Complete stabilization using electron cyclotron current drive (ECCD) has been demonstrated at beta(N)= 2.5 and with about 10% of the total heating power. The results are in good qualitative agreement with modelling using the Rutherford equation and in quantitative agreement with a two-dimensional non-linear cylindrical tearing mode code. A precise positioning of the ECCD microwave beam, so far achieved by feed forward variation of B[t] , is required for efficient stabilization. This calls for feedback control of the stabilization scheme. Our plans to implement such a scheme on ASDEX Upgrade are discussed.

Additional information

Authors: ZOHM H, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);GUDE A, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);GNTER S, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);LEUTERER F, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);MARASCHEK M, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);SUTTROP W, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);YU Q, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);ASDEX UPGRADE TEAM, MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);ECRH-GROUP (AUG), MPI f³r Plasmaphysik, EURATOM Association, Garching (DE);GANTENHEIN G, Institut f³r Plasmaforschung, Stuttgard (DE);MESKAT J, Institut f³r Plasmaforschung, Stuttgard (DE)
Bibliographic Reference: An article published in: Physics of Plasmas. Vol.8, No.5 (2001), pp.2009-2016
Record Number: 200013477 / Last updated on: 2001-06-29
Category: PUBLICATION
Original language: en
Available languages: en
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