Drift-based scrape-off particle width in X-point geometry. (23rd February 2017)

• Record Type: Journal Article
• Authors: Reiser, D.; Eich, T.
• Is Part Of: Nuclear fusion. Volume 57:Number 4(2017:Apr.)
• Publication Date: 2017-02-23
• Subjects: tokamak -- SOL decay length -- SOL width -- drift-based transport -- 2D fluid model; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/aa5ab7
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: The Goldston heuristic estimate of the scrape-off layer width (Goldston 2012 Nucl. Fusion 52 013009 ) is reconsidered using a fluid description for the plasma dynamics. The basic ingredient is the inclusion of a compressible diamagnetic drift for the particle cross field transport. Instead of testing the heuristic model in a sophisticated numerical simulation including several physical mechanisms working together, the purpose of this work is to point out basic consequences for a drift-dominated cross field transport using a reduced fluid model. To evaluate the model equations and prepare them for subsequent numerical solution a specific analytical model for 2D magnetic field configurations with X-points is employed. In a first step parameter scans in high-resolution grids for isothermal plasmas are done to assess the basic formulas of the heuristic model with respect to the functional dependence of the scrape-off width on the poloidal magnetic field and plasma temperature. Particular features in the 2D-fluid calculations—especially the appearance of supersonic parallel flows and shock wave like bifurcational jumps—are discussed and can be understood partly in the framework of a reduced 1D model. The resulting semi-analytical findings might give hints for experimental proof and implementation in more elaborated fluid simulations.