a2 Max-Planck-Institut für Plasmaphysik, Euratom Association, D-85748 Garching, Germany (email@example.com)
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. Fusion 46, 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.
(Received March 10 2006)
† A preliminary version of this study was presented at the 10th European Fusion Theory Conference (Helsinki, Finland, 8–10 September 2003).