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Abstract

The existence of a partially chaotic magnetic topology in the confinement zone of Tokamaks could explain the anomalous heat transport observed in ohmically heated plasmas relative to classical perpendicular diffusion, and the degradation of confinement at high levels of heating power. An analysis, based on non-dimensional structural parameters which describe the dominant physical processes in the plasma, is interpreted in terms of a critical electron temperature gradient, above which the heat diffusivity is anomalous. The critical value of nablaT-"rm e", a local quantity, when applied to small islands is reached when several chains of magnetic islands--of a size comparable to the ion Larmor radius--are embedded in a common chaotic region. This situation is already expected to occur in the ohmic phase. These arguments are substantiated by a physical model and consistent expressions of nabla-"rm c"T-"rm e" and of chi-"an" are tested against JET experimental data on the basis of global scalings and of more detailed transport code simulations.

Additional information

Authors: LALLIA P P, JET JOINT UNDERTAKING, ABINGDON (UK);REBUT P H, JET JOINT UNDERTAKING, ABINGDON (UK);WATKINS M L JET JOINT UNDERTAKING, ABINGDON (UK), JET JOINT UNDERTAKING, ABINGDON (UK)
Bibliographic Reference: AVAILABILITY: PUBLICATIONS OFFICER, JET JOINT UNDERTAKING, ABINGDON, OXON, OX14 3EA (UK) MENTIONING REPORT JET-P(88)05, 1988
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