Speaker
Description
Since the early 90ties, 3D nonlinear MHD studies have been developing a fundamental framework for the understanding of the Reversed Field Pinch (RFP) self-organization. The simple visco-resistive MHD approximation clearly shows that 3D reconnection processes strongly characterize the dynamics in an ample range of the dimensionless Lundquist/Hartmann numbers, as well as in experimental discharges [1-9]. In fact, this is particularly evident during the nearly periodic relaxation-reconnection events (so-called RFP sawtoothing activity) observed in both Multiple and Quasi Helical regimes where the natural kinking of the current carrying plasma column triggers relaxations with localized shrinking/collapse of the global helical magnetic field perturbation. In this presentation we will provide a survey of the typical magnetic reconnection manifestation in nonlinear visco-resistive MHD of the RFP and some comparison with the similar behavior in the circular tokamak case. The main features are: magnetic into kinetic energy conversion (possibly providing ion heating), 3D current sheets formation and related flow patterns, mode phase locking, (toroidal collapse of the helix), excitation of Alfvén waves. The possibility to “tune” the sawtooth cycle by adopting suitable Resonant or Non resonant Magnetic Perturbation will be also presented. How much extended-MHD physics would be necessary to better capture the RFP experimental phenomenology still remains to be clarified, and we expect to address this aspect with the help of the RFX-mod2 device under renovation.
References:
[1] S. Cappello and D. Biskamp, Reconnection processes and scaling laws in reversed field pinch magnetohydro dynamics Nucl. Fusion 36 571(1996)
[2] S. Cappello, Bifurcation in the MHD behaviour of a self-organizing system: the reversed field pinch (RFP) Plasma Phys. Control. Fusion 46 B313 (2004)
[3] D. Bonfiglio, et al., Sawtooth mitigation in 3D MHD tokamak modelling with applied magnetic perturbations Plasma Phys. Control. Fusion 59 014032 (2017)
[4] M. Veranda, Helically self-organized pinches: dynamical regimes and magnetic chaos healing Nucl Fus 60 016007 (2020)
[5] M. Veranda et al., Magnetic reconnection in three‑dimensional quasi‑helical pinches, Rend. Fis. Acc. Lincei 31, 963–984 (2020),
[6] A. Kryzhanovskyy et al., Alfvén waves in reversed-field pinch and tokamak ohmic plasmas: nonlinear 3D MHD modeling and comparison with RFX-mod, Nucl. Fusion 62 086019 (2022)
[7] B. Momo et al The phenomenology of reconnection events in the reversed field pinch Nucl. Fus 60 056023 (2020)
[8] M. Gobbin et al., Ion heating and energy balance during magnetic reconnection events in the RFX-mod experiment
Nucl. Fusion 62 026030 (2022)
[9] L. Marrelli et al, The Reversed Field Pinch Nucl. Fusion 61 023001 (2021)
