Speaker
Description
Advanced numerical tools play a determinant role in the understanding of plasma dynamics. The nonlinear three-dimensional magneto-hydrodynamic (3D MHD) code SPECYL [1] investigates magnetic self-organisation processes in fusion plasmas in the Reversed Field Pinch (RFP) and in the tokamak configurations. In the past, SPECYL has been used to investigate the Quasi Single Helicity states (QSH) in the RFP devices [2], where the dominance of a single component in the magnetic field spectrum sustains dynamo currents [3] and fosters the plasma confinement: QSH states in RFP plasmas are strongly influenced by the magnetic boundary [4]. Analogous self-organised helical structures have also been studied with SPECYL in the hybrid equilibria of tokamak plasmas [5,6].
We present the implementation and verification against the independent 3D MHD nonlinear code PIXIE3D [7,8] of more realistic boundary conditions, featuring fully 3D boundary flow and including with increasing complexity a thin shell of variable resistivity in contact with the plasma, surrounded by an arbitrarily wide vacuum region that separates it from an outer ideal conductor [9]. This is a versatile formulation, capable of reproducing different experimental conditions: from an ideal wall attached to the plasma, to a free interface between plasma and vacuum, to a physical wall of finite resistivity at plasma boundary.
In the free plasma-vacuum interface regime, the 3D boundary flow is proven to have an essential role in reproducing free-boundary instabilities, such as the external kink modes in the tokamak configuration. Remarkably, the new implementation of SPECYL’s BCs is indeed shown to be capable of achieving robust and self-consistent agreement with the theoretical figures of merit of linear MHD [10], with great freedom of choice in the initial equilibrium and without the need of a pseudo-vacuum boundary region.
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.
[1] S. Cappello, D. Biskamp: “Reconnection processes and scaling laws in reversed field pinch magnetohydrodynamics” Nucl. Fus., 36, 571 (2008)
[2] D. Bonfiglio, M. Veranda, S. Cappello, D. F. Escande, L. Chacόn: “Experimental-like helical self-organization in reversed-field pinch modeling” PRL, 111, 085002 (2013)
[3] S. Cappello, D. Bonfiglio, D. F. Escande: “Magnetohydrodynamic dynamo in reversed field pinch plasmas: electrostatic drift nature of the dynamo velocity field” Phys. Plasmas, 13, 056102 (2006)
[4] M. Veranda, D. Bonfiglio, S. Cappello, et al.: “Magnetohydrodynamics modelling successfully predicts new helical states in reversed-field pinch fusion plasmas” Nucl. Fus., 57, 11, 116029 (2017)
[5] D. Bonfiglio, M. Veranda, S. Cappello, D. F. Escande, L. Chacόn: “Helical self-organization in 3D MHD modelling of fusion plasmas” Plasma Phys. Contr. Fusion, 57, 044001 (2015)
[6] P. Piovesan, D. Bonfiglio, et al.: “Role of a continuous MHD dynamo in the formation of 3D equilibria in fusion plasmas” Nucl. Fus., 57, 076014 (2017)
[7] L. Chacόn: “A non-staggered, conservative, ∇⋅b=0 finite volume scheme for 3d implicit extended magnetohydrodynamics in curvilinear geometries” Computer Phys. Communications, 163, 143-171 (2004)
[8] D. Bonfiglio, L. Chacόn, S. Cappello: “Nonlinear threedimensional verification of the SPECYL and PIXIE3D magnetohydrodynamics codes for fusion plasmas” Phys. Plasmas, 17, 082501 (2010)
[9] L. Spinicci: “3D Nonlinear MHD modelling studies: Plasma Flow and Realistic Magnetic Boundary Impact on Magnetic self-organisation in Fusion Plasmas”, PhD Thesis, chap. 7-8 (2023)
[10] J. P. Freidberg: “Ideal MHD”, chap. 8 and 11, Cambridge Univ. Press (2014)
