One can show that the radial drift a particle experiences after one full bounce motion is simply related to a derivative of J , ∂ ∂ J ∂ ∂ α α = q Δ Δ ψ ψ where q is the charge of the particle, α α is the magnetic field line label, and Δ Δ ψ ψ is the total radial drift expressed as a difference in toroidal flux. With this relation, omnigeneity can be expressed as the criterion that the second adiabatic invariant should be the same for all the magnetic field lines on a flux surface, ∂ ∂ J ∂ ∂ α α = 0 This criterion is exactly met in axisymmetric systems, as the derivative with respect to α α can be expressed as a derivative with respect to the toroidal angle (under which the system is invariant).