Nonlinear 3D MHD physics of the helical reversed-field pinch

The main results from nonlinear 3D MHD simulations of the reversed-field pinch (RFP) will be presented, with a particular emphasis on the physics of the helical RFP states which are also experimentally observed, with the occurrence of internal transport barriers, in the RFX-mod device [1]. The recently benchmarked extended MHD code PIXIE3D [2] enables the inclusion of additional physics in the RFP simulations, like toroidal effects and the coupling with transport. The reduction of magnetic chaos in helical RFP states is confirmed by means of the field line tracing code NEMATO [3]. The evidence of magnetic shear reversal [4] and sheared plasma flows [5] in MHD simulations and their relation with the experimental observations will be also discussed. [1] R. Lorenzini et al., Nature Phys. 5 (2009) 570 [2] D. Bonfiglio et al., Phys. Plasmas 17 (2010) 082501 [3] D. Bonfiglio et al., J. Phys.: Conf. Ser. 260 (2010) 012003 [4] M. Gobbin et al., Phys. Rev. Lett. 106 (2011) 025001 [5] D. Bonfiglio et al., in Proceedings of the 37th EPS Conference on Plasma Physics (Dublin, 2010) http://ocs.ciemat.es/EPS2010PAP/pdf/O2.101.pdf