Hybrid guiding-centre/full-orbit simulations in non-axisymmetric magnetic geometry exploiting general criterion for guiding-centre accuracy

D. Pfefferlé, J. P. Graves, W. A. Cooper

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

To identify under what conditions guiding-centre or full-orbit tracing should be used, an estimation of the spatial variation of the magnetic field is proposed, not only taking into account gradient and curvature terms but also parallel currents and the local shearing of field-lines. The criterion is derived for general three-dimensional magnetic equilibria including stellarator plasmas. Details are provided on how to implement it in cylindrical coordinates and in flux coordinates that rely on the geometric toroidal angle. A means of switching between guiding-centre and full-orbit equations at first order in Larmor radius with minimal discrepancy is shown. Techniques are applied to a MAST (mega amp spherical tokamak) helical core equilibrium in which the inner kinked flux-surfaces are tightly compressed against the outer axisymmetric mantle and where the parallel current peaks at the nearly rational surface. This is put in relation with the simpler situation B(x, y, z) = B0[sin(kx)ey + cos(kx)ez], for which full orbits and lowest order drifts are obtained analytically. In the kinked equilibrium, the full orbits of NBI fast ions are solved numerically and shown to follow helical drift surfaces. This result partially explains the off-axis redistribution of neutral beam injection fast particles in the presence of MAST long-lived modes (LLM).

Original languageEnglish
Article number054017
JournalPlasma Physics and Controlled Fusion
Volume57
Issue number5
DOIs
Publication statusPublished - 1 May 2015
Externally publishedYes

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  • Activities

    • 1 Contribution or participation in a conference

    Joint Varenna-Lausanne International Workshop on Theory of Fusion Plasmas 2014

    David Pfefferle (Keynote speaker/Invited speaker)

    1 Sep 20145 Sep 2014

    Activity: Conferences and workshopsContribution or participation in a conference

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