Advanced numerical tools play a determinant role in the understanding of plasma dynamics. From the early 90’s the nonlinear three-dimensional magneto-hydrodynamic (3D MHD) code SPECYL [1] investigates magnetic self-organisation processes in fusion plasmas, and predominantly the Quasi-Single Helicity (QSH) states in the Reversed Field Pinch (RFP) devices [2]. QSH states consist in the dominance of a saturated resistive-kink or tearing mode, sustaining dynamo currents [3] and enhancing the plasma confinement: their spontaneous emergence is influenced by internal plasma parameters such as resistivity and viscosity [4] and by the magnetic boundary.We present the implementation and verification of more realistic boundary conditions, featuring a thin shell of variable resistivity in contact with the plasma, surrounded by a vacuum region and by an outer ideal conductor [5,6]. 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. A nonlinear verification benchmark is presented against the independent 3D MHD code PIXIE3D [7], enforcing equivalent physical assumptions at plasma boundary: this is a substantial extension of a previous successful verification study performed in 2010 with much simpler boundary conditions [8]. Faithfulness to physical behaviour is also illustrated through the benchmark against analytical models, describing ubiquitous relaxation processes as the kink modes and the tearing modes in the large aspect-ratio tokamak.[1]S. Cappello et al., American Institute of Physics 978-0-7354-0600 (2008)
[2]R. Lorenzini, E. Martinez, P. Piovesan et al., Nature Phys., 5, 570-574 (2009)
[3]S. Cappello, D. Bonfiglio, D. F. Escande, Phys. of Plasm., 13, 056102 (2006)
[4]N. Vivenzi, G. Spizzo, M. Veranda, D. Bonfiglio, S. Cappello et al, J. of Phys. – Conference series, 1, 012010 (2022)
[5]D. Bonfiglio, S. Cappello, D. F. Escande, G. Di Giannatale, A. Kryzhanovskyy, M. Veranda, L. Marrelli, P. Zanca, 46th EPS Conference, Milan, P1.1049 (2019)
[6]L. Spinicci, D. Bonfiglio, L. Chacόn, S. Cappello, M. Veranda, 8th EPS conference proceedings, #79, P5b.102 (1st July 2022)
[7]L. Chacόn, 33rd EPS conference proceedings, 30I, 1.164, (19-23 June 2006)
[8]D. Bonfiglio, L. Chacόn, S. Cappello, Phys. of Pl., 17, 082501 (2010)
