Kinetic approach to a pressure-gradient-driven tokamak resistive instability in the banana regime

A new resistive, low-frequency (ω≪ω_ba∼ν _a, where ω is the frequency of the mode and ω_ba and ν_a are the bounce frequency and collision frequency for species a) instability is found in a tokamak geometry. The mode is driven unstable by the parallel viscous (bootstrap) current induced by the radial pressure gradient. It has a growth rate γ∼(ω _*e²ν_i)^1/3 for ν_i≫ω_*e, where ω_*e is the electron diamagnetic drift frequency and ν_i is the ion-ion collision frequency. The frequency dependence of the parallel viscosity is also derived and utilized to show that drift wave branches of these modes are stable, but that this new mode remains unstable when the diamagnetic drift effects are included.