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Abstract

Internal transport barriers (ITB) observed in tokamaks are described by a purely magnetic approach. Magnetic line motion in toroidal geometry with broken magnetic surfaces is studied from a previously derived Hamiltonian map in situation of incomplete chaos. This appears to reproduce in a realistic way the main features of a tokamak, for a given safety factor profile and in terms of a single parameter L representing the amplitude of the magnetic perturbation. New results are given concerning the Shafranov shift as function of L.

Single trajectories of magnetic line motion indicate the persistence of a central protected plasma core, surrounded by a chaotic shell enclosed in a double-sided transport barrier: the latter is identified as being composed of two Cantori located on two successive "most-noble" numbers values of the perturbed safety factor, and forming an ITB. Magnetic lines that succeed to escape across this barrier begin to wander in a wide chaotic sea extending up to a very robust barrier which is identified mathematically as a robust KAM surface at the plasma edge. In this case the motion is shown to be intermittent, with long stages of pseudo-trapping in the chaotic shell, or of sticking around island segments, as expected for a continuous time random walk.

Additional information

Authors: MISGUICH J H, Association Euratom-CEA, CEA Cadarache, Saint-Paul-lez-Durance (FR);REUSS J-D, Association Euratom-CEA, CEA Cadarache, Saint-Paul-lez-Durance (FR);CONSTANTINESCU D, Association Euratom-NASTI, University of Craiova (RO);STEINBRECHER G, Association Euratom-NASTI, University of Craiova (RO);VLAD M, Association Euratom-NASTI, National Institute of Laser, Plasma and Radiation Physics, Bucharest (RO);SPINEANU F, Association Euratom-NASTI, National Institute of Laser, Plasma and Radiation Physics, Bucharest (RO);WEYSSOW B, Association Euratom-État Belge sur la Fusion, Université Libre de Bruxelles (BE);BALESCU R, Association Euratom-État Belge sur la Fusion, Université Libre de Bruxelles (BE)
Bibliographic Reference: Report EUR-CEA-FC-1724 (February 2002), pp.85. Free of charge
Availability: Available from: Association EURATOM-CEA, Département de Recherches sur la Fusion Contrôlée, 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
Record Number: 200215027 / Last updated on: 2002-07-26
Category: PUBLICATION
Original language: en
Available languages: en
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