Symplectic integration of guiding-center equations in canonical coordinates for general toroidal fields

Abstract Symplectic integrators with long-term preservation of integrals of motion are introduced for the guiding-center motion of plasma particles in the toroidal magnetic fields of general topology. An efficient transformation to canonical coordinates from cylindrical and flux-like coordinates is discussed and applied using a single component of the magnetic vector potential as a spatial coordinate. This choice is efficient in both theoretical and numerical developments and marks a generalization of magnetic flux coordinates. The transformation enables the application of conventional symplectic integration schemes formulated in canonical coordinates, as well as variational integrators on the guiding-center system, without requiring magnetic flux coordinates. Symplectic properties and superior efficiency of the implicit midpoint scheme compared to conventional non-symplectic methods are demonstrated on perturbed tokamak fields with magnetic islands and stochastic regions. The presented findings are benchmarked against symplectic integration in canonicalized flux coordinates and Boozer coordinates on energetic particle losses in 3D magnetic configurations.