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Abstract

A systematic procedure to identify the plasma equilibrium response to the poloidal field coil voltages has been applied to the JT-60U tokamak. The required response was predicted with a high accuracy by a state-space model derived from first principles. The ab initio derivation of linearized plasma equilibrium response models is re-examined using an approach standard in analytical mechanics. A symmetric formulation is naturally obtained, removing a previous weakness in such models. RZIP, a rigid current distribution model, is re-derived using this approach and is compared with the new experimental plasma equilibrium response data obtained from Ohmic and neutral beam injection discharges in the JT-60U tokamak. In order to remove any bias from the comparison between modelled and measured plasma responses, the electromagnetic response model without plasma was first carefully tuned against experimental data, using a parametric approach, for which different cost functions for quantifying model agreement were explored. This approach additionally provides new indications of the accuracy to which various plasma parameters are known, and to the ordering of physical effects. Having taken these precautions when tuning the plasmaless model, an empirical estimate of the plasma self-inductance, the plasma resistance and its radial derivative could be established and compared with initial assumptions. Off-line tuning of the JT-60U controller is presented as an example of the improvements which might be obtained by using such a model of the plasma equilibrium response.

Additional information

Authors: LISTER J B, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH);SHARMA A, Imperial College of Science, Technology and Medicine, Centre for Process Systems Engineering, London (GB);LIMEBEER D J N, Imperial College of Science, Technology and Medicine, Centre for Process Systems Engineering, London (GB);WAINWRIGHT J P, Imperial College of Science, Technology and Medicine, Centre for Process Systems Engineering, London (GB);NAKAMURA Y, JAERI Naka Fusion Research Establishment, Naka-machi, Naka-gun, Ibaraki-ken (JP);YOSHINO R, JAERI Naka Fusion Research Establishment, Naka-machi, Naka-gun, Ibaraki-ken (JP)
Bibliographic Reference: An article published in: Nuclear Fusion 42 (June 2002) pp.708-724
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://stacks.iop.org/0029-5515/42/708
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