Kinetic theory of helical instabilities in a cylindrical tokamak

The kinetic theory of the drift-tearing mode in a finite-β, collisionless inhomogeneous cylindrical tokamak is investigated. It is found that 1) when the density is low, the kinetic drift-tearing modes are unstable whereas they become stabilized as the density increases, 2) the medium-m (poloidal mode number) modes have a smaller growth rate, and 3) the electron temperature gradient further stabilizes these modes. Because of the magnetic shear and the finite β value, the outgoing drift wave is associated with the tearing mode, and hence the ion Landau damping stabilizes the mode when β increases. The local current density is found to be crucial for the instability. It is noted that the stability criterion for the MHD tearing mode, Δ'<0(Δ' is the jump of the logarithmic derivative of B tildesub(r) across the mode rational surface), is no longer valid for kinetic tearing mode. - For future tokamak parameters, low- and medium-m (2<=m approximately <50) kinetic drift-tearing modes are found to be stable in cylindrical geometry. (author)