2013 Volume 8 Pages 1403170
Guiding-center equations for relativistic particles are presented in axisymmetric toroidal geometry using Boozer coordinates. Effects of slow equilibrium changes are included for describing electron acceleration due to the induction field, which is a fundamental process of runaway electron generation during disruptions. For a consistent treatment of the runaway orbit in finite-pressure plasmas, the equations are given in both canonical and noncanonical forms by retaining the radial covariant component of the equilibrium magnetic field. For this purpose, the Lagrangian formulation by White and Zakharov [R.B. White and L.E. Zakharov, Phys. Plasmas 10, 573 (2003)] is applied to axisymmetric equilibria with slowly varying magnetic-flux functions.