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Two sources of magnetic diagnostic drift have been well documented, namely electronic input offset of the integrators, since the fields and fluxes are time-integrals of the voltages from the physical probes, and radiation induced or thermoelectric emf due to neutron bombardment of the mineral insulated cables between the probes and the integrators. Tore Supra has recently demonstrated an additional effect, not previously taken into consideration, which is slight rotation of the magnetic probes by thermo-mechanical distortion during 300 second pulses absorbing more than 1GJ into the plasma, resulting in time-dependent pick-up of the toroidal magnetic field. The Tore Supra control system tracks these offsets and displaces the last closed flux surface from its reference location. This new effect of long high-power pulses has the properties of a drift, generating a slowly evolving unmeasured offset to the integrated magnetic signals. For this reason, we have decided to take another look at methods of reconstructing an offset-free equilibrium from magnetic diagnostics, whereas most proposed approaches to drift compensation rely on non-magnetic, non-integrated measurements of plasma emission or reflectometry. We note that a similar approach was tested on HT-7 [1] using the induction in the Poloidal Field (PF) coils as the sole measurement of the radial position, modulating in a similar way. Although this present work uses magnetic diagnostics, we are extending this idea to include the vertical position and the deformation of highly shaped plasmas.

Additional information

Authors: LISTER J B, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confederation Suisse, Ecole Polytechnique Federale de Lausanne (CH);SAINT-LAURENT F, Departement de Recherches sur la Fusion Controlee, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);MOREAU PH, Departement de Recherches sur la Fusion Controlee, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);DOKOUKA V., TRINITI, Moscow Region (RU);KHAYRUTDINOV R R, TRINITI, Moscow Region (RU);LUKASH V E, RRC Kurchatov Institute, Moscow (RU)
Bibliographic Reference: An oral paper given at: 31st EPS Conference on Controlled Fusion and Plasma Physics Organised by: CCLRC Rutherford Appleton Laboratory (GB); EURATOM/UKAEA Fusion Association (GB) Held at: Imperial College London(GB)
Availability: Available from Association EURATOM-CEA, Departement de Recherches sur la Fusion Controlee, CEA Cadarache, F-13108 St Paul-Lez-Durance, France Tel: (+33) 4 42 25 70 01; Fax: (+33) 4 42 25 64 21 E-mail:
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