  The effect of a narrow sub-Alfvenic shear flow layer near the minimum q_min
of the tokamak safety factor profile in a configuration with reversed central
shear is analyzed. Sufficiently strong velocity shear gives rise to a broad
spectrum of fast growing Kelvin-Helmholtz (KH)-like ideal magnetohydrodynamic
(MHD) modes with dominant mode numbers m,n ~ 10. Nonlinear simulations with
finite resistivity show magnetic reconnection near ripples caused by KH-like
vortices, the formation of turbulent structures, and a flattening of the flow
profile. The KH modes are compared to double tearing modes (DTM) which dominate
at lower shearing rates. The possible application of these results in tokamaks
with internal transport barrier is discussed.
