Numerical drift orbit calculations for force-free spheromak configurations

A numerical analysis was performed of guiding-center (gc) orbits in a variety of spheromaktype force-free, numerically determined equilibria including the normal spherical configurations as well as configurations that are more prolate and oblate, and others having hollow or peaked current profiles. The calculated drift orbits differ significantly from the well-known drift orbits in tokamaks. In particular, the results indicate (i) the existence of particles trapped in separate hemispheres, (ii) the orbit widths d are about proportional to the Larmor radius ρ of the particle (calculated for the field maximum) up to ρ≈0.01-0.02 of the major separatrix dimension, (iii) many orbits, in particular on the outer flux lines, have their maximum normalized width d _max/ρ_L(ρ_L = local Larmor radius) away from the midplane of the configuration, and (iv) these maximum normalized widths are about 2-4 over most of the volume for all configurations except for prolate ones with a peaked current profile; in the latter configurations, orbits on outer field surfaces show d_max ≤ρ_L.