Particle and heat diffusion fluxes due to toroidal drift of bananas in helical solenoids, i.e. solenoids wound around a circular torus, are discussed. Particle collision frequency ranges, in which the effective trapped-particle collision frequency is lower than the inverse trapped-particle period of oscillation between the magnetic mirrors, but higher than the frequency of banana precession around the magnetic axis, are considered. It is shown that for this regime the diffusion coefficients in helical solenoids may be greater than those in a three-turn stellarator, but smaller than those in stellarator-type traps with a helical magnetic axis produced by the magnetic fields of the helical windings.
Effect of magnetic-surface cross-sections on maximum equilibrium plasma pressure in toroidal traps with helical magnetic axis