DOI number: 10.1088/1741-4326/aad2a5

Journal: Nuclear Fusion

Key Words: collisionless pitch-angle scattering, magnetic moment, runaway electron

Abstract: Recently, the validity of the guiding-center approach to model relativistic runaway electrons in tokamaks has been challenged by full-orbit simulations that demonstrate the breakdown of the standard magnetic moment conservation. In this paper, we derive a new expression for the magnetic moment of relativistic runaway electrons with , which is conserved significantly better than the standard one. The new result includes one of the second-order corrections in the standard guiding-center theory which, in case of runaway electrons with , can peculiarly be of the same order as the lowest-order term. The better conservation of the new magnetic moment also explains the collisionless pitch-angle-scattering effect observed in full-orbit simulations since it allows momentum transfer between the perpendicular and parallel directions when the runaway electron is accelerated by an electric field. While the derivation of the second-order correction to the magnetic moment in general case would require the full extent of the relativistic second-order guiding-center theory, we exploit the Lie-perturbation method at the limit which simplifies the computations significantly. Consequently, we present the corresponding guiding-center equations applicable to runaway electrons.

Co-author: Chang Liu,Hong Qin,Eero Hirvijokl,Yulei Wang,Jian Liu

Discipline: Natural Science

Volume: 58

Issue: 10

Page Number: 106018

Translation or Not: no

Date of Publication: 2018-08-03

Included Journals: SCI

Links to published journals: https://www.osti.gov/biblio/1460954