Radial differential operator

The form of the radial differential operator $\nabla \Psi \cdot \nabla$ in $(\psi, \theta, \zeta)$ coordinates is given by

$$\nabla \Psi \cdot \nabla = \Psi' \vert \nabla \psi \vert^2 \frac{... ...eta} + \Psi' (\nabla \psi \cdot \nabla \zeta) \frac{\partial}{\partial \zeta} .$$ (167)

(Refer to my notes ``tokamak_equilibrium.tm'' for the proof.)