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Two-fluid tokamak equilibria with reversed magnetic shear and sheared flow†

Published online by Cambridge University Press:  01 June 2007

G. POULIPOULIS ,
G. N. THROUMOULOPOULOS  and
H. TASSO
G. POULIPOULIS
Affiliation:
University of Ioannina, Association Euratom – Hellenic Republic, Section of Theoretical Physics, GR 451 10 Ioannina, Greece ([email protected]; [email protected])
G. N. THROUMOULOPOULOS
Affiliation:
University of Ioannina, Association Euratom – Hellenic Republic, Section of Theoretical Physics, GR 451 10 Ioannina, Greece ([email protected]; [email protected])
H. TASSO
Affiliation:
Max-Planck-Institut für Plasmaphysik, Euratom Association, D-85748 Garching, Germany ([email protected])
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Abstract

The aim of the present work is to investigate tokamak equilibria with reversed magnetic shear and sheared flow, which may play a role in the formation of internal transport barriers (ITBs), within the framework of the two-fluid model in cylindrical geometry. The study is based on exact self-consistent solutions by means of which the impact of the magnetic shear, s, and the ‘toroidal’ (axial) and ‘poloidal’ (azimuthal) ion velocity components, viz and viθ, on the radial electric field, Er, its shear, |dEr/dr|, and the shear of the E×B velocity, ωE×B≡|d/dr(E× B/B2)|, is examined. For a wide parametric regime of experimental concern it turns out that the contributions of the viz, viθ and pressure gradient (∇ Pi) terms to Er, |Er′| and ωE×B are of the same order of magnitude. The contribution of the ∇ Pi term is missing in the framework of magnetohydrodynamics (MHD) (G. Poulipoulis et al. 2004 Plasma Phys. Control. Fusion46, 639). The impact of s on ωE×B through the ∇ Pi term is stronger than that through the velocity terms; in particular for constant Bz the ion pressure gradient contribution to ωE×B at the point where dEr/dr=0 scales as (1−s)(2−s), whereas the ion flow contributions to ωE×B scale as (1−s). The results indicate that, like MHD, the magnetic shear and the sheared toroidal and poloidal velocities act synergetically in producing electric fields and therefore ωE×B profiles compatible with the ones observed in discharges with ITBs; owing to the ∇ Pi term, however, the impact of s on Er, |Er′| and ωE×B is stronger than that in MHD.

Type
Papers
Information
Journal of Plasma Physics , Volume 73 , Issue 3 , June 2007 , pp. 347 - 366
Copyright
Copyright © Cambridge University Press 2006

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