This derivation is only used for Tokamaks, but it can be enlightening. Using the definition of 'The Theory of Toroidally Confined Plasmas 1:3'(Roscoe White), Writing B → → by contravariant basis ( ∇ ∇ Ψ Ψ , ∇ ∇ ϕ ϕ , ∇ ∇ ζ ζ ) : B → → = ∇ ∇ Ψ Ψ × × ∇ ∇ ϕ ϕ + F ¯ ¯ ∇ ∇ ϕ ϕ ,