416 research outputs found
Impact of dissipative effects on the macroscopic evolution of a Vlasov system
Numerical diffusion is introduced by any numerical scheme as soon as small
scales fluctuations, generated during the dynamical evolution of a
collisionless plasma, become comparable to the grid size. Here we investigate
the role of numerical dissipation in collisionless plasma simulations by
studying the non linear regime of the two stream instability. We show that the
long time evolution of the Vlasov - Poisson system can be affected by the used
algorithm.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Pressure anisotropy and small spatial scales induced by velocity shear
Non-Maxwellian metaequilibria can exist in low-collisionality plasmas as
evidenced by satellite and laboratory measurements. By including the full
pressure tensor dynamics in a fluid plasma model, we show that a sheared
velocity field can provide an effective mechanism that makes an initial
isotropic state anisotropic and agyrotropic. We discuss how the propagation of
magneto-elastic waves can affect the pressure tensor anisotropization and its
spatial filamentation which are due to the action of both the magnetic field
and flow strain tensor. We support this analysis by a numerical integration of
the nonlinear equations describing the pressure tensor evolution.Comment: 5 pages, 3 Figure
Propagation of finite amplitude electrostatic disturbances in an inhomogeneous magnetized plasma
A 1D2V open boundary Vlasov-Ampere code has been implemented with the aim of
making a detailed investigation of the propagation of finite amplitude
electromagnetic disturbances in an inhomogeneous magnetized plasma. The code is
being applied to study the propagation of an externally driven electromagnetic
signal, localized at one boundary of the integration interval, through a given
equilibrium plasma configuration with inhomogeneous plasma density and magnetic
field.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Coupling between whistler waves and slow-mode solitary waves
The interplay between electron-scale and ion-scale phenomena is of general
interest for both laboratory and space plasma physics. In this paper we
investigate the linear coupling between whistler waves and slow magnetosonic
solitons through two-fluid numerical simulations. Whistler waves can be trapped
in the presence of inhomogeneous external fields such as a density hump or hole
where they can propagate for times much longer than their characteristic time
scale, as shown by laboratory experiments and space measurements. Space
measurements have detected whistler waves also in correspondence to magnetic
holes, i.e., to density humps with magnetic field minima extending on
ion-scales. This raises the interesting question of how ion-scale structures
can couple to whistler waves. Slow magnetosonic solitons share some of the main
features of a magnetic hole. Using the ducting properties of an inhomogeneous
plasma as a guide, we present a numerical study of whistler waves that are
trapped and transported inside propagating slow magnetosonic solitons.Comment: Submitted to Phys. of Plasma
Being on time in magnetic reconnection
The role of magnetic reconnection on the evolution of the Kelvin-Helmholtz instability is investigated in a plasma configuration with a velocity shear field. It is shown that the rate at which the large-scale dynamics drives the formation of steep current sheets, leading to the onset of secondary magnetic reconnection instabilities, and the rate at which magnetic reconnection occurs compete in shaping the final state of the plasma configuration. These conclusions are reached within a two-fluid plasma description on the basis of a series of two-dimensional numerical simulations. Special attention is given to the role of the Hall term. In these simulations, the boundary conditions, the symmetry of the initial configuration and the simulation box size have been optimized in order not to affect the evolution of the system artificially
Nonlinear kinetic development of the Weibel instability and the generation of electrostatic coherent structures
The nonlinear evolution of the Weibel instability driven by the anisotropy of the electron distribution function in a collisionless plasma is investigated in a spatially one-dimensional configuration with a Vlasov code in a two-dimensional velocity space. It is found that the electromagnetic fields generated by this instability cause a strong deformation of the electron distribution function in phase space, corresponding to highly filamented magnetic vortices. Eventually, these deformations lead to the generation of short wavelength Langmuir modes that form highly localized electrostatic structures corresponding to jumps of the electrostatic potential
Kelvin-Helmholtz vortices and secondary instabilities in super-magnetosonic regimes
The nonlinear behaviour of the Kelvin-Helmholtz instability is investigated with a two-fluid simulation code in both sub-magnetosonic and super-magnetosonic regimes in a two-dimensional configuration chosen so as to represent typical conditions observed at the Earth's magnetopause flanks. It is shown that in super-magnetosonic regimes the plasma density inside the vortices produced by the development of the Kelvin-Helmholtz instability is approximately uniform, making the plasma inside the vortices effectively stable against the onset of secondary instabilities. However, the relative motion of the vortices relative to the plasma flow can cause the formation of shock structures. It is shown that in the region where the shocks are attached to the vortex boundaries the plasma conditions change rapidly and develop large gradients that allow for the onset of secondary instabilities not observed in sub-magnetosonic regimes
Subion Scale Turbulence Driven by Magnetic Reconnection
The interplay between plasma turbulence and magnetic reconnection remains an
unsettled question in astrophysical and laboratory plasmas. Here we report the
first observational evidence that magnetic reconnection drives subion scale
turbulence in magnetospheric plasmas by transferring energy to small scales. We
employ a spatial coarse-grained model of Hall magnetohydrodynamics, enabling us
to measure the nonlinear energy transfer rate across scale at position
. Its application to Magnetospheric Multiscale mission data shows that
magnetic reconnection drives intense energy transfer to subion scales. This
observational evidence is remarkably supported by the results from Hybrid
Vlasov-Maxwell simulations of turbulence to which the coarse-grained model is
also applied. These results can potentially answer some open questions on
plasma turbulence in planetary environments
Spectral properties and energy transfer at kinetic scales in collisionless plasma turbulence
By means of a fully kinetic simulation of freely decaying plasma turbulence,
we study the spectral properties and the energy exchanges characterizing the
turbulent cascade in the kinetic range. We find that the magnetic field
spectrum follows the law at kinetic scales
with and (where is
the electron gyroradius). The same law with and an
exponential decay characterized by is observed in
the electron velocity spectrum but not in the ion velocity spectrum that drops
like a steep power law before reaching electron scales. By
analyzing the filtered energy conversion channels, we find that the electrons
play a major role with respect to the ions in driving the magnetic field
dynamics at kinetic scales. Our analysis reveals the presence of an indirect
electron-driven mechanism that channels the e.m. energy from large to sub-ion
scale more efficiently than the direct nonlinear scale-to-scale transfer of
e.m. energy. This mechanism consists of three steps: in the first step the e.m.
energy is converted into electron fluid flow energy at large scales; in the
second step the electron fluid flow energy is nonlinearly transferred towards
sub-ion scales; in the final step the electron fluid flow energy is converted
back into e.m. energy at sub-ion scales. This electron-driven transfer drives
the magnetic field cascade up to fully developed turbulence, after which
dissipation becomes dominant and the electrons start to subtract energy from
the magnetic field and dissipate it via the pressure-strain interaction at
sub-ion scales
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