The role of finite–orbit effects in the theory of short–wavelength non-potential oscillations in a tokamak plasma

The paper investigates the non-potential (non-electrostatic) perturbations of a plasma contained in a toroidal magnetic trap of the tokamak type. The transverse wavelengths are assumed to be small in comparison with the ion Larmor radius. It considers the case of perturbations considerably extended along the lines of force of a magnetic field k||qR < 1 (where k|| is the longitudinal wave number, q the tokamak safety factor and R the radius of curvature of the magnetic axis). It is shown that in this case the dispersion relation for short-wavelength non-potential perturbations is affected substantially by the effects of the finite orbits of the transit ions. The dispersion relation for such perturbations is obtained; it differs substantially from that for similar perturbations in a straight magnetic field. It is pointed out that these perturbations can grow as a result of electron dissipation.