Symplectic integration with non-canonical quadrature for guiding-center orbits in magnetic confinement devices

Christopher G. Albert*, Sergei V. Kasilov, Winfried Kernbichler

*Korrespondierende/r Autor/in für diese Arbeit

Publikation: Beitrag in einer FachzeitschriftArtikel

Abstract

We study symplectic numerical integration of mechanical systems with a Hamiltonian specified in non-canonical coordinates and its application to guiding-center motion of charged plasma particles in magnetic confinement devices. The technique combines time-stepping in canonical coordinates with quadrature in non-canonical coordinates and is applicable in systems where a global transformation to canonical coordinates is known explicitly but its inverse is not. A fully implicit class of symplectic Runge-Kutta schemes has recently been introduced and applied to guiding-center motion by Zhang et al. (2014) [9]. Here a generalization of this approach with emphasis on semi-implicit partitioned schemes is described together with methods to enhance performance, in particular avoiding evaluation of non-canonical variables at full time steps. For application in toroidal plasma confinement configurations with nested magnetic flux surfaces a global canonicalization of coordinates for the guiding-center Lagrangian by a spatial transform is presented that allows for pre-computation of the required map in a parallel algorithm in the case of time-independent magnetic field geometry. Guiding-center orbits are studied in stationary magnetic equilibrium fields of an axisymmetric tokamak and a realistic three-dimensional stellarator configuration. Superior long-term properties of symplectic methods are demonstrated in comparison to a conventional adaptive Runge-Kutta scheme. Finally statistics of fast fusion alpha particle losses over their slowing-down time are computed in the stellarator field on a representative sample, reaching a speed-up of the symplectic Euler scheme by more than a factor three compared to usual Runge-Kutta schemes while keeping the same statistical accuracy and linear scaling with the number of computing threads.
Originalspracheenglisch
Aufsatznummer109065
Seitenumfang23
FachzeitschriftJournal of Computational Physics
Jahrgang403
DOIs
PublikationsstatusVeröffentlicht - 15 Feb 2020

ASJC Scopus subject areas

  • !!Computational Mathematics
  • !!Physics and Astronomy(all)
  • Angewandte Mathematik
  • Numerische Mathematik
  • !!Computer Science Applications
  • !!Modelling and Simulation
  • !!Physics and Astronomy (miscellaneous)

Fields of Expertise

  • Information, Communication & Computing

Kooperationen

  • NAWI Graz

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