I2.J101

43rd EPS Conference on Plasma Physics
I2.J101
Connections between RFP, Tokamak and Stellarator physics as
highlighted in 3D nonlinear MHD modelling
D. Bonfiglio1, S. Cappello1, D.F. Escande2,1, M. Veranda1,
D. Borgogno3, L. Chacón4, D. Grasso5, G. Rubino6
1
Consorzio RFX, Padova, Italy 2 Aix-Marseille Université, CNRS, PIIM, Marseille, France
3
Université Cote d’Azur, CNRS, Observatoire de la Cote d’Azur, Nice, France
4
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
5
Istituto dei Sistemi Complessi-CNR, Politecnico di Torino, Torino, Italy
6
ENEA, Fusion and Technologies for Nuclear Safety Department, Frascati, Italy
The understanding of fusion plasmas benefits from investigating the same phenomena in
different magnetic configurations such as the tokamak, the stellarator, and the reversed-field
pinch (RFP) [1-4]. Here, the same approach is applied in the framework of nonlinear 3D
MHD modelling. We first focus on sawtoothing, i.e., the quasiperiodic magnetic relaxation
of RFP and tokamak plasmas. Sawtoothing manifests itself together with magnetic
reconnection events, and with the formation of current sheets and of dynamo electric fields.
Such processes are relevant to laboratory and astrophysical plasmas as well. In both tokamak
and RFP configurations, sawtoothing is quenched leading to long-lasting helical states
whenever visco-resistive dissipation is increased [5,6] or small helical magnetic
perturbations (MPs) are applied [7,8]. A similar effect of MPs has been observed in the
RFX-mod device [9]. We secondly consider the topological properties of partially ergodic
magnetic fields, which characterize helical states in the RFP [7]. Barriers to the stochastic
diffusion of field lines (the so-called cantori also studied in the tokamak configuration [10])
are diagnosed in the weakly stochastic core of the helical RFP [11], which could explain
experimentally observed internal transport barriers. Chains of magnetic islands naturally
occur at the RFP edge [12]. Such chains may be exploited to realize a so-called island
divertor, which may alleviate plasma-wall interactions like in the stellarator [3]. Numerical
results are provided by two MHD codes, successfully benchmarked against one another [6].
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[7] D. Bonfiglio, M. Veranda, S. Cappello et al., Phys. Rev. Lett. 111 (2013) 085002
[8] D. Bonfiglio, M. Veranda, S. Cappello et al., Plasma Phys. Control. Fusion 57 (2015) 044001
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