26 research outputs found
Fourier-Hermite decomposition of the collisional Vlasov-Maxwell system: implications for the velocity space cascade
Turbulence at kinetic scales is an unresolved and ubiquitous phenomenon that
characterizes both space and laboratory plasmas. Recently, new theories, {\it
in-situ} spacecraft observations and numerical simulations suggest a novel
scenario for turbulence, characterized by a so-called phase space cascade --
the formation of fine structures, both in physical and velocity space. This new
concept is here extended by directly taking into account the role of
inter-particle collisions, modeled through the nonlinear Landau operator or the
simplified Dougherty operator. The characteristic times, associated with
inter-particle correlations, are derived in the above cases. The implications
of introducing collisions on the phase space cascade are finally discussed.Comment: Special issue featuring the invited talks from the International
Congress on Plasma Physics (ICPP) in Vancouver, Canada 4-8 June 201
Fourier-Hermite decomposition of the collisional Vlasov-Maxwell system: Implications for the velocity-space cascade
Turbulence at kinetic scales is an unresolved and ubiquitous phenomenon that characterizes both space and laboratory plasmas. Recently, new theories, {\it in-situ} spacecraft observations and numerical simulations suggest a novel scenario for turbulence, characterized by a so-called phase space cascade -- the formation of fine structures, both in physical and velocity space. This new concept is here extended by directly taking into account the role of inter-particle collisions, modeled through the nonlinear Landau operator or the simplified Dougherty operator. The characteristic times, associated with inter-particle correlations, are derived in the above cases. The implications of introducing collisions on the phase space cascade are finally discussed
Turbulence-driven ion beams in space plasmas
The description of the local turbulent energy transfer and the high-resolution ion distributions measured by the Magnetospheric Multiscale mission together provide a formidable tool to explore the cross-scale connection between the fluid-scale energy cascade and plasma processes at subion scales. When the small-scale energy transfer is dominated by Alfv´enic, correlated velocity, and magnetic field fluctuations, beams of accelerated particles are more likely observed. Both space observations and numerical simulations suggest the nonlinear wave-particle interaction as one possible mechanism for the energy dissipation in space plasmas
Turbulence generation during the head-on collision of Alfvénic wave packets.
The description of the Moffatt and Parker problem recently revisited by O. Pezzi et al. [Astrophys. J. 834, 166 (2017)1538-435710.3847/1538-4357/834/2/166] is here extended by analyzing the features of the turbulence produced by the interaction of two colliding Alfvénic wave packets in a kinetic plasma. Although the approach based on the presence of linear modes features is still helpful in characterizing some low-energy fluctuations, other signatures, which go beyond the pure linear modes analysis, are recovered, such as the significant weakening of clear dispersion relations and the production of zero frequency fluctuations
ViDA: a VlasovDArwin solver for plasma physics at electron scales
We present a Vlasov–DArwin numerical code (ViDA) specifically designed to
address plasma physics problems, where small-scale high accuracy is requested
even during the nonlinear regime to guarantee a clean description of the plasma
dynamics at fine spatial scales. The algorithm provides a low-noise description of
proton and electron kinetic dynamics, by splitting in time the multi-advection Vlasov
equation in phase space. Maxwell equations for the electric and magnetic fields are
reorganized according to the Darwin approximation to remove light waves. Several
numerical tests show that ViDA successfully reproduces the propagation of linear and
nonlinear waves and captures the physics of magnetic reconnection. We also discuss
preliminary tests of the parallelization algorithm efficiency, performed at CINECA
on the Marconi-KNL cluster. ViDA will allow the running of Eulerian simulations
of a non-relativistic fully kinetic collisionless plasma and it is expected to provide
relevant insights into important problems of plasma astrophysics such as, for instance,
the development of the turbulent cascade at electron scales and the structure and
dynamics of electron-scale magnetic reconnection, such as the electron diffusion
region
Turbulence-driven ion beams in the magnetospheric Kelvin-Helmholtz instability
The description of the local turbulent energy transfer via a heuristic proxy derived from the third-order moment scaling law, and the high-resolution ion distributions measured by the Magnetospheric Multiscale mission, together provide a formidable tool to explore the cross-scale connection between the fluid-scale energy cascade and plasma processes at sub-ion scales. Using magnetospheric boundary layers measurements, we show that when the small-scale energy transfer is dominated by Alfvénic, correlated velocity and magnetic field fluctuations, beams of accelerated particles are more likely observed. Here, for the first time we report observations suggesting the nonlinear wave-particle interaction as one possible mechanism for the energy dissipation in space plasmas