Transport modelling for ergodic configuration

Runov, A.; Zagórski, R.; Reiter, D.; Kasilov, S. V.; McTaggart, N.; Bonnin, X.; Schneider, R.

doi:10.1088/0029-5515/44/6/S08

Journal Article

Transport modelling for ergodic configuration

Runov, A. ; Kasilov, S. V. ; McTaggart, N. ; Schneider, R. ; Bonnin, X. ; Zagórski, R.FZJ* ; Reiter, D.FZJ*

2004
IAEA Vienna

Nuclear fusion 44, s74 - s82 (2004) [10.1088/0029-5515/44/6/S08]

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Please use a persistent id in citations: http://hdl.handle.net/2128/1830 doi:10.1088/0029-5515/44/6/S08

Abstract: The effect of ergodization, either by additional coils like in TEXTOR-dynamic ergodic divertor (DED) or by intrinsic plasma effects like in W7-X, defines the need for transport models that are able to describe the ergodic configuration properly. A prerequisite for this is the concept of local magnetic coordinates allowing a correct discretization with minimized numerical errors. For these coordinates the appropriate full metric tensor has to be known. To study the transport in complex edge geometries (in particular for W7-X) two possible methods are used.First, a finite-difference discretization of the transport equations on a custom-tailored grid in local magnetic coordinates is used. This grid is generated by field-line tracing to guarantee an exact discretization of the dominant parallel transport (thus also minimizing the numerical diffusion problem). The perpendicular fluxes are then interpolated in a plane (a toroidal cut), where the interpolation problem for a quasi-isotropic system has to be solved by a constrained Delaunay triangulation (keeping the structural information for magnetic surfaces if they exist) and discretization. All toroidal terms are discretized by finite differences.Second, a Monte Carlo transport model originally developed for the modelling of the DED configuration of TEXTOR is used. A generalization and extension of this model was necessary to be able to handle W7-X. The model solves the transport equations with Monte Carlo techniques making use of mappings of local magnetic coordinates. The application of this technique to W7-X in a limiter-like configuration is presented. The decreasing dominance of parallel transport with respect to radial transport for electron heat, ion heat and particle transport results in increasingly steep profiles for the respective quantities within the islands.

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