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(THP1/26) Effects of Tokamak Flux Surface Non-circularity on Charged Particle Transport Processes in the Weak Collisionality Regime

K. Schoepf¹⁾, B. H. Cho¹⁾, V. Ya. Goloborod'ko²⁾, S. N. Reznik²⁾, V. A. Yavorskij^2)
 
1) Institut für Theoretische Physik, Universität Innsbruck, Assoz. EURATOM-ÖAW, Austria
²⁾ Institute for Nuclear Research, Ukrainian Academy of Sciences, Kyiv, Ukraine

Abstract.  Introducing a novel analytical model for tokamak fields with prescribed flux surface shapes into a 3D Fokker-Planck simulation, the influence of parameters determining the non-circularity of flux surfaces on the longitudinal transport of charged particles as well as on their radial fluxes is investigated for weak collisionality. It is demonstrated that a high triangularity can decrease the trapped particle fraction by up to 30%. An increase of elongation and triangularity at fixed plasma current and fixed B was found to reduce the effective radial excursion of charged particles thus resulting in the improvement of plasma confinement. An extreme sensitivity of the NBI induced current to the flux surface non-circularity was seen for Z_beam $\approx$ Z_eff. Another interesting result is that the triangularity and up-down asymmetry of flux surface strongly affect the slowing-down induced radial convection of high-energy toroidally trapped charged particles being in resonance with the TF ripple perturbation. This transport mechanism is deemed to be consequential for the confinement of charged fusion products in tokamaks. Further the ripple-induced stochastic transport domains are shown to vary with flux surface shapes.

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