On the theory and application of drift motion of charged particles in inhomogeneous magnetic fields

A drift theory, valid for any ratio of particle gyroradius to scale length of field variations, is presented as an alternative to guiding centre drift theory. Local instantaneous drift expressions are derived for simple forms of particle velocity distribution functions in terms of the fields at the particles. The main advantage of this particle drift concept above the standard guiding centre drift is that the relationship between particle current, particle drift current and circulation current may be written down per definition. A clear distinction is made between these three quantities. It is shown that the particle drift speed for an isotropic distribution, when viewed on the scale of a gyroradius, cannot exceen (π/4)v. Trajectory traced drift velocities are used to show under what circumstances this limit of drift speed is attained. Total drift velocity fields are calculated for cases when the magnetic field has a neutral plane across which it changes direction. Three methods for the incorporation of neutral sheet drift into the transport equation for galactic cosmic rays are evaluated. An extension to the case of a wavy neutral sheet is discussed