Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X

Alberto Gallo 1 Nicolas Fedorczak 1 Sarah Elmore 2 Roberto Maurizio 3 Holger Reimerdes 3 Christian Theiler 3 Cedric Tsui 3, 4 Jose Boedo 4 Michael Faitsch 5 Hugo Bufferand 1 Guido Ciraolo 1 Davide Galassi 6 Philippe Ghendrih 1 Matteo Valentinuzzi 7 Patrick Tamain 8
1 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique
2 CCFE - Culham Centre for Fusion Energy
3 SPC - Swiss Plasma Center
4 UC San Diego - University of California [San Diego]
5 IPP-MPG - Max Planck Institute for Plasma physics
6 M2P2 - Laboratoire de Mécanique, Modélisation et Procédés Propres
7 PIIM - Physique des interactions ioniques et moléculaires
8 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
Abstract : A deep understanding of plasma transport at the edge of magnetically confined fusion plasmas is needed for the handling and control of heat loads on the machine first wall. Experimental observations collected on a number of tokamaks over the last three decades taught us that heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two scale lengths for the scrape-off layer (SOL) transport, separately characterizing the main SOL (${\lambda }_{q}$) and the divertor SOL (S q ). In this work we challenge the current interpretation of these two scale lengths as well as their dependence on plasma parameters by studying the effect of divertor geometry modifications on heat exhaust in the Tokamak à Configuration Variable. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg in lower single null, Ohmic, L-mode discharges. Efforts to reproduce this experimental finding with both diffusive (SolEdge2D-EIRENE) and turbulent (TOKAM3X) modelling tools confirm the validity of a diffusive approach for simulating heat flux profiles in more traditional, short leg, configurations while highlighting the need of a turbulent description for modified, long leg, ones in which strongly asymmetric divertor perpendicular transport develops.
Keywords : scrape-off layer transport divertor magnetic geometry heat load characterization
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Alberto Gallo, Nicolas Fedorczak, Sarah Elmore, Roberto Maurizio, Holger Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014007. ⟨10.1088/1361-6587/aa857b⟩. ⟨hal-02114145⟩

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