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

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, vizand vi?, on the radial electric field, Er, its shear, |dEr/dr|, and the shear of the E?Bvelocity, ?E?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, vi? and pressure gradient (Pi) terms to Er, |Er?| and ?E?Bare of the same order of magnitude. The contribution of the Piterm is missing in the framework of magnetohydrodynamics (MHD) (G. Poulipoulis et al. 2004 Plasma Phys. Control. Fusion46, 639). The impact of son ?E?Bthrough the Piterm is stronger than that through the velocity terms; in particular for constant Bzthe ion pressure gradient contribution to ?E?Bat the point where dEr/dr=0 scales as (1?s)(2?s), whereas the ion flow contributions to ?E?Bscale 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 ?E?Bprofiles compatible with the ones observed in discharges with ITBs; owing to the Piterm, however, the impact of son Er, |Er?| and ?E?Bis stronger than that in MHD. [ABSTRACT FROM AUTHOR]