IRIS Uni Torinohttps://iris.unito.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Sat, 22 Jan 2022 14:15:58 GMT2022-01-22T14:15:58Z1031Linear wave propagation for resistive relativistic magnetohydrodynamicshttp://hdl.handle.net/2318/1693405Titolo: Linear wave propagation for resistive relativistic magnetohydrodynamics
Abstract: We present a linear mode analysis of the relativistic magnetohydrodynamics equations in the presence of finite electrical conductivity. Starting from the fully relativistic covariant formulation, we derive the dispersion relation in the limit of small linear perturbations. It is found that the system supports ten wave modes which can be easily identified in the limits of small or large conductivities. In the resistive limit, matter and electromagnetic fields decouple and solution modes approach pairs of light and acoustic waves as well as a number of purely damped (non-propagating) modes. In the opposite (ideal) limit, the frozen-in condition applies and the modes of propagation coincide with a pair of fast magnetosonic, a pair of slow and Alfvén modes, as expected. In addition, the contact mode is always present and it is unaffected by the conductivity. For finite values of the conductivity, the dispersion relation gives rise to either pairs of opposite complex conjugate roots or purely imaginary (damped) modes. In all cases, the system is dissipative and also dispersive as the phase velocity depends nonlinearly on the wavenumber. Occasionally, the group velocity may exceed the speed of light although this does not lead to superluminal signal propagation.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/2318/16934052018-01-01T00:00:00ZA constrained transport method for the solution of the resistive relativistic MHD equationshttp://hdl.handle.net/2318/1721257Titolo: A constrained transport method for the solution of the resistive relativistic MHD equations
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/2318/17212572019-01-01T00:00:00ZA Particle Module for the PLUTO Code. I. An Implementation of the MHD–PIC Equationshttp://hdl.handle.net/2318/1685776Titolo: A Particle Module for the PLUTO Code. I. An Implementation of the MHD–PIC Equations
Abstract: We describe an implementation of a particle physics module available for the PLUTO code appropriate for the dynamical evolution of a plasma consisting of a thermal fluid and a nonthermal component represented by relativistic charged particles or cosmic rays (CRs). While the fluid is approached using standard numerical schemes for magnetohydrodynamics, CR particles are treated kinetically using conventional Particle-In-Cell (PIC) techniques. The module can be used either to describe test-particle motion in the fluid electromagnetic field or to solve the fully coupled magnetohydrodynamics (MHD)-PIC system of equations with particle backreaction on the fluid as originally introduced by Bai et al. Particle backreaction on the fluid is included in the form of momentum-energy feedback and by introducing the CR-induced Hall term in Ohm’s law. The hybrid MHD-PIC module can be employed to study CR kinetic effects on scales larger than the (ion) skin depth provided that the Larmor gyration scale is properly resolved. When applicable, this formulation avoids resolving microscopic scales, offering substantial computational savings with respect to PIC simulations. We present a fully conservative formulation that is second-order accurate in time and space, and extends to either the Runge-Kutta (RK) or the corner transport upwind time-stepping schemes (for the fluid), while a standard Boris integrator is employed for the particles. For highly energetic relativistic CRs and in order to overcome the time-step restriction, a novel subcycling strategy that retains second-order accuracy in time is presented. Numerical benchmarks and applications including Bell instability, diffusive shock acceleration, and test-particle acceleration in reconnecting layers are discussed.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/2318/16857762018-01-01T00:00:00Z