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Understanding the mechanisms responsible for particle transport is of the utmost importance for magnetized fusion plasmas. A peaked density profile is attractive to improve the fusion rate, which is proportional to the square of the density, and to self-generate a large fraction of non-inductive current required for continuous operation. Experiments in various tokamak devices (ASDEX Upgrade, DIII-D, JET, TCV, TEXT, TFTR) indicate the existence of a turbulent particle pinch. Recently, such a turbulent pinch has been unambiguously identified in Tore Supra very long discharges, in the absence of both collisional particle pinch and central particle source, for more than 4 min. This turbulent pinch is predicted by a quasilinear theory of particle transport, and confirmed by nonlinear turbulence simulations and general considerations based on the conservation of motion invariants. Experimentally, the particle pinch is found to be sensitive to the magnetic field gradient in many cases, to the temperature profile and also to the collisionality that changes the nature of the microturbulence. The consistency of some of the observed dependences with the theoretical predictions gives us a clearer understanding of the particle pinch in tokamaks, allowing us to predict more accurately the density profile in ITER.

Additional information

Authors: BOURDELLE C, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion, Vol. 47 (2005), p. A317-A326
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