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Abstract

Long plasma discharges on the Tore Supra tokamak, first sustained by LHCD alone, were extended in 2004 towards higher powers and plasma densities by combined LH and ICRF waves. More than the mere extrapolation of shorter ones, long pulses raise specific issues combining technology, experiments and modelling.
Tore Supra is equipped with 3 ICRF antennas including 2 straps in metallic boxes, shielded by a B4C-coated Faraday Screen, and surrounded by CFC lateral protections, all actively cooled. They reach constant surface temperatures after several seconds. Cooling constraints at generators and VTLs limit pulse energies to 3×120MJ, for a full RF power of 3×4MW. In 2004 RF pulses of 20s×8MW and 60s×4MW were produced.
Antennas are monitored by calorimetry and infrared cameras, documenting the heat flux localisation, parametric dependencies, and thermal time constants. At least 3 processes were thus identified: convected power, electrons accelerated in the LH near field, and a RF mechanism compatible with RF sheaths. A hot spot asymmetry was observed between different box corners, which reversed upon B(0) reversal. LH coupling was also perturbed in the antenna shadow. This was attributed to RF-induced DC E×B(0) convection.
This motivated sheath modelling in two directions. First, the 2D topology of RF potentials was investigated in relation with the RF current distribution over the antenna, via a Green�s function formalism and full-wave calculation using the antenna code ICANT. In front of phased arrays of straps, convective cells were interpreted using the profiles of either RF current or RF voltage of strip line theory. Another class of convective cells, specific to antenna box corners, was evidenced for the first time.

Additional information

Authors: COLAS L, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);BREMOND S, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);MITTEAU R, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);CHANTANT M, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);GONICHE M, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);BASIUK V, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);BOSIA G, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);FAUDOT E, LPMIA, Unité du CNRS 7040, Université Henri Poincaré, Nancy (FR);HEURAUX S, LPMIA, Unité du CNRS 7040, Université Henri Poincaré, Nancy (FR)
Bibliographic Reference: An oral paper given at: Sixteenth Topical Conference on Radio Frequency Power in Plasmas Organised by: Plasma Science & Fusion Center, Cambridge (US) Held at: Park City, Utah USA
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: dirdrfc@drfc.cad.cea.fr
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