350 research outputs found
Turbulence evolution in MHD plasmas
Turbulence in the interstellar medium has been an active field of research in
the last decade. Numerical simulations are the tool of choice in most cases.
But while there are a number of simulations on the market some questions have
not been answered finally. In this paper we are going to examine the influence
of compressible and incompressible driving on the evolution of turbulent
spectra in a number of possible interstellar medium scenarios. We conclude that
the driving not only has an influence on the ratio of compressible to
incompressible component but also on the anisotropy of turbulence.Comment: Accepted for publication in Journal of Plasma Physic
High-energy particle transport in 3D hydrodynamic models of colliding-wind binaries
Massive stars in binary systems (as WR140, WR147 or Carinae) have long
been regarded as potential sources of high-energy -rays. The emission
is thought to arise in the region where the stellar winds collide and produce
relativistic particles which subsequently might be able to emit -rays.
Detailed numerical hydrodynamic simulations have already offered insight in the
complex dynamics of the wind collision region (WCR), while independent
analytical studies, albeit with simplified descriptions of the WCR, have shed
light on the spectra of charged particles. In this paper, we describe a
combination of these two approaches. We present a 3D-hydrodynamical model for
colliding stellar winds and compute spectral energy distributions of
relativistic particles for the resulting structure of the WCR. The hydrodynamic
part of our model incorporates the line-driven acceleration of the winds,
gravity, orbital motion and the radiative cooling of the shocked plasma. In our
treatment of charged particles we consider diffusive shock acceleration in the
WCR and the subsequent cooling via inverse Compton losses (including
Klein-Nishina effects), bremsstrahlung, collisions and other energy loss
mechanisms.Comment: 28 pages, 9 figures / accepted for publication in The Astrophysical
Journa
MHD Simulation of the Inner-Heliospheric Magnetic Field
Maps of the radial magnetic field at a heliocentric distance of ten solar
radii are used as boundary conditions in the MHD code CRONOS to simulate a 3D
inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The
input data for the magnetic field are the result of solar surface flux
transport modelling using observational data of sunspot groups coupled with a
current sheet source surface model. Amongst several advancements, this allows
for higher angular resolution than that of comparable observational data from
synoptic magnetograms. The required initial conditions for the other MHD
quantities are obtained following an empirical approach using an inverse
relation between flux tube expansion and radial solar wind speed. The
computations are performed for representative solar minimum and maximum
conditions, and the corresponding state of the solar wind up to the Earths
orbit is obtained. After a successful comparison of the latter with
observational data, they can be used to drive outer-heliospheric models.Comment: for associated wmv movie files accompanying Figure 7, see
http://www.tp4.rub.de/~tow/max.wmv and http://www.tp4.rub.de/~tow/min.wm
A low dissipation essentially nonoscillatory central scheme
Abstract Here we present a new, semi-discrete, central scheme for the numerical solution of one-dimensional systems of hyperbolic conservation laws. The method presented in this paper is an extension of the methods presented in [1]
Diffusion of energetic particles in turbulent MHD plasmas
In this paper we investigate the transport of energetic particles in
turbulent plasmas. A numerical approach is used to simulate the effect of the
background plasma on the motion of energetic protons. The background plasma is
in a dynamically turbulent state found from numerical MHD simulations, where we
use parameters typical for the heliosphere. The implications for the transport
parameters (i.e. pitch-angle diffusion coefficients and mean free path) are
calculated and deviations from the quasi-linear theory are discussed.Comment: Accepted for publication in Ap
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