Kinematic viscosity estimates in reversed-field pinch fusion plasmas

Vivenzi, N.; Spizzo, G.; Veranda, M.; Bonfiglio, D.; Cappello, S.

doi:10.1088/1742-6596/2397/1/012010

Cited by 2 publications

(1 citation statement)

References 42 publications

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“…For this reason, the experimental values for the viscosity and diffusion coefficients need to be approximated. As a recent study of RFPs shows, it is not easy to approximate the experimentally relevant fusion parameters for the viscoresistive MHD model, even when relying on significant experimental data [33].…”

Section: Simulations With Experimental Spitzer Resistivitymentioning

confidence: 99%

Nonlinear MHD modeling of soft β limits in W7-AS

Ramasamy,

Aleynikova,

Nikulsin

et al. 2024

Nucl. Fusion

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An important question for the outlook of stellarator reactors is their robustness against pressure driven modes, and the underlying mechanism behind experimentally observed soft β limits. Towards building a robust answer to these questions, simulation studies are presented using a recently derived reduced nonlinear MHD model. First, the initial model implementation is extended to capture fluid compression by including the influence of parallel flows. Linear benchmarks of a (2, 1) tearing mode in W7-AS geometry, and interchange modes in a finite β, net-zero current carrying stellarator with low magnetic shear are then used to demonstrate the modeling capabilities. Finally, a validation study is conducted on experimental reconstructions of finite β W7-AS discharges. In agreement with past experimental analysis, it is shown that (i) the MHD activity is resistive, (ii) a soft β limit is observed, when the plasma resistivity approaches the estimated experimental value, and (iii) low n MHD activity is observed at intermediate β values, particularly a nonlinearly dominant (2, 1) mode. The MHD activity is mild, explaining the soft β limit, because the plasma volume remains separated into distinct sub-volumes in which field lines are ergodically confined. For the assumed transport parameters, the enhanced perpendicular transport along stochastic magnetic field lines can be overcome with the experimental heating power. The limitations in the current modeling are described, alongside an outlook for characterizing the quasi-steady state operational limit in W7-AS and other devices in more detail in future work.

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Section: Simulations With Experimental Spitzer Resistivitymentioning

confidence: 99%

Nonlinear MHD modeling of soft β limits in W7-AS

Ramasamy,

Aleynikova,

Nikulsin

et al. 2024

Nucl. Fusion

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show abstract

Viscosity impact on 3D non-linear MHD simulations of RFP fusion plasmas

et al. 2023

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Several studies pointed out the joint role of resistivity η and viscosity ν in determining the dynamics and the emergence of helical regimes of reversed-field pinch (RFP) plasmas. In this framework, the self-consistent time evolution of the η and ν coefficients still lacks of a fully satisfying modeling, being constrained by many approximations. In this work, the hypothesis of a flat viscosity profile is relaxed: A viscosity profile inspired by the Braginskii perpendicular viscosity is implemented in the code. This choice is motivated by the fact that the magnetohydrodynamics field instabilities relevant for the RFP configuration dynamics (resistive-kink/tearing modes) are active in the direction perpendicular to the magnetic field. Such a non-monotonous profile causes a localized damping of plasma flow in the regions, where the viscosity is stronger, close to the plasma edge. This results in the reduction of the flow shear, in turn allowing the enhancement of edge magnetic field modes amplitude. The impact on the magnetic topology and on connection length to the wall is also analyzed.

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Kinematic viscosity estimates in reversed-field pinch fusion plasmas

Cited by 2 publications

References 42 publications

Nonlinear MHD modeling of soft β limits in W7-AS

Nonlinear MHD modeling of soft β limits in W7-AS

Viscosity impact on 3D non-linear MHD simulations of RFP fusion plasmas

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