Topology during magnetic reconnection events in RFX-mod

RFX-mod is a medium-sized device (R₀=2 m, a=0.459 m) operated by Consorzio RFX, that mainly works in the Reversed-Field Pinch (RFP) magnetic confinement configuration. During a typical RFP discharge, long phases of high confinement with helical symmetry are interrupted by reconnection events¹ associated with significant Plasma-Wall Interaction (PWI), which is the topic of this work. An example of reconnection event has been observed via a fast camera looking at the graphite-covered inner wall, showing two separated footprints². A first analysis, considering the reconstruction of the last closed plasma surface deformation due to phase-locking of m=1 tearing modes as the main cause of PWI shows that more modes than those measured by magnetic sensors are locked. A more refined analysis, involving the calculation of a 3D map of the Connection Length to the wall with the Hamiltonian guiding center code ORBIT, confirms the importance of m=1 phase-locking but an additional role of the m=0, n=7 mode is highlighted, which is a new result for the RFP. Finally, a further analysis considering a synthetic spectrum of tearing modes with m=0, 1 and n<45 reproduces the PWI pattern in detail.

¹M. Gobbin et al., Nucl. Fusion 62, 026030 (2022)

²P. Scarin et al., Nucl. Fusion 59, 086008 (2019)