期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 516, 期 4, 页码 5143-5147出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stac2523
关键词
MHD; plasmas; methods: numerical; cosmic rays; ISM: structure; galaxies: evolution
资金
- Caltech
- Natural Science Foundation of China [12133008, 12192220, 12192223]
- China Manned Space Project [CMS-CSST-2021-B02]
- NSF [1911233, 20009234]
- NSF CAREER [1455342]
- NASA [80NSSC18K0562, HST-AR-15800.001-A]
- NSF
- TACC
- NASA HEC [SMD-16-7592]
- High Performance Computing Resource in the Core Facility for Advanced Research Computing at Shanghai Astronomical Observatory
The reduced speed-of-light (RSOL) approximation is a useful technique in MHD-PIC simulations, but existing simulations may have artificial variations in CR properties. This study proposes a new formulation of the MHD-PIC equations with an RSOL, ensuring steady-state properties of the CR distribution function and representing real physical values in simulations.
A reduced speed-of-light (RSOL) approximation is a useful technique for magnetohydrodynamic (MHD)-particle-in-cell (PIC) simulations. With an RSOL, some 'in-code' speed-of-light (c) over tilde is set to much lower values than the true c, allowing simulations to take larger time-steps (which are restricted by the Courant condition given the large CR speeds). However, due to the absence of a well-formulated RSOL implementation from the literature, with naive substitution of the true c with a RSOL, the CR properties in MHD-PIC simulations (e.g. CR energy or momentum density, gyro radius) vary artificially with respect to each other and with respect to the converged ((c) over tilde -> c) solutions, with different choices of a RSOL. Here, we derive a new formulation of the MHD-PIC equations with an RSOL, and show that (1) it guarantees all steady-state properties of the CR distribution function, and background plasma/MHD quantities are independent of the RSOL (c) over tilde even for (c) over tilde << c; (2) it ensures that the simulation can simultaneously represent the real physical values of CR number, mass, momentum, and energy density; (3) it retains the correct physical meaning of various terms like the electric field; and (4) it ensures the numerical time-step for CRs can always be safely increased by a factor similar to c/(c) over tilde. This new RSOL formulation should enable greater self-consistency and reduced CPU cost in simulations of CR-MHD interactions.
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