Scalable matrix-free solver for 3D transfer of polarized radiation in stellar atmospheres

Benedusi, Pietro; Riva, Simone; Zulian, Patrick; Štĕpán, Jiri; Belluzzi, Luca; Krause, Rolf

doi:10.1016/j.jcp.2023.112013

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Journal article

Scalable matrix-free solver for 3D transfer of polarized radiation in stellar atmospheres

Benedusi, Pietro ORCID Simula Research Laboratory, Oslo, Norway ; Euler Institute (EUL), Università della Svizzera italiana, Switzerland
Riva, Simone ORCID Euler Institute (EUL), Università della Svizzera italiana, Switzerland ; Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Facoltà di scienze informatiche, Università della Svizzera italiana, Svizzera
Zulian, Patrick ORCID Euler Institute (EUL), Università della Svizzera italiana, Switzerland
Štĕpán, Jiri Astronomical Institute of the Czech Academy of Sciences, Ondˇrejov, Czech Republic
Belluzzi, Luca ORCID Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Facoltà di scienze informatiche, Università della Svizzera italiana, Svizzera ; Leibniz-Institut für Sonnenphysik (KIS), Freiburg i. Br., Germany ; Euler Institute (EUL), Università della Svizzera italiana, Switzerland
Krause, Rolf ORCID Euler Institute (EUL), Università della Svizzera italiana, Switzerland ; Faculty of Mathematics and Informatics, FernUni, Brig, Switzerland

2023

Published in:

Journal of computational physics. - 2023, vol. 479, p. 112013

English We present an efficient and massively parallel solution strategy for the transfer problem of polarized radiation, for a 3D stationary medium out of local thermodynamic equilibrium. Scattering processes are included accounting for partial frequency redistribution effects. Such a setting is one of the most challenging ones in radiative transfer modeling. The problem is formulated for a two-level atomic model, which allows linearization. The discrete ordinate method alongside an exponential integrator are used for discretization. Efficient solution is obtained with a Krylov method equipped with a tailored physics-based preconditioner. A matrix-free approach results in a lightweight implementation, suited for tackling large problems. Near-optimal strong and weak scalability are obtained with two complementary decompositions of the computational domain. The presented approach made it possible to perform simulations for the Cailine at 4227Å with more than 109degrees of freedom in less than half an hour on massively parallel machines, always converging in a few iterations for the proposed tests.

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