Collisionless drift modes in a toroidal configuration

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Abstract
Toroidicity-induced drift modes are investigated in the collisionless regime. Ion magnetic drift resonant effects are fully retained, also in the ion sound contribution. It is shown that the modes with the least number of nodes between turning points are localized at the outside of the torus within the poloidal interval (- pi , pi ). They are marginally stable and their amplitudes vanish before the magnetic drift resonance is actually reached. Any inverse dissipation will destabilize the lowest even mode. Here, the destabilization due to inverse Landau damping of circulating electrons is investigated. The non-adiabatic response of trapped electrons causes a decrease of the mode frequency. For normal Tokamak parameters, the maximum growth rate is a few times 10-2 omega * and occurs at kperpendicular to rho i*.