Alfvén waves in RFP plasmas: nonlinear 3D MHD modeling and comparison with RFX-mod

We report a recent modeling study on Alfvén waves in reversed-field pinch plasmas, and the comparison with experimental findings in the RFX-mod device. The nonlinear 3D MHD cylindrical code SpeCyl [1] has been used to analyze configurations with increasing level of complexity. First of all, numerical solutions have been compared with analytical ones in the most simple case of a uniform axial magnetic field: an excellent agreement is obtained for both the shear Alfvén wave (SAW) and the compressional Alfvén eigenmodes (CAEs). Then, the RFP configuration has been studied by assuming perturbations with a single space periodicity. Phenomena such as phase mixing of SAW, resonant absorption of CAEs and the appearance of the global Alfvén eigenmode (GAE) are reported. Finally, the fully 3D RFP case with realistic magnetic reconnection events [2] has been investigated, showing for the first time in nonlinear RFP simulations the excitation of Alfvén waves by magnetic reconnection. Modeling results are in good quantitative agreement with the experimental characterization of Alfvénic activity observed in RFX-mod [3]. [1] S. Cappello and D. Biskamp, Nucl. Fusion 36 (1996) 571 [2] D. Bonfiglio et al., Phys. Rev. Lett. 111 (2013) 085002 [3] S. Spagnolo et al., Nucl. Fusion 51 (2011) 083038