9,690 research outputs found
Kinetic cascade in solar-wind turbulence: 3D3V hybrid-kinetic simulations with electron inertia
Understanding the nature of the turbulent fluctuations below the ion
gyroradius in solar-wind turbulence is a great challenge. Recent studies have
been mostly in favor of kinetic Alfv\'en wave (KAW) type of fluctuations, but
other kinds of fluctuations with characteristics typical of magnetosonic,
whistler and ion Bernstein modes, could also play a role depending on the
plasma parameters. Here we investigate the properties of the sub-proton-scale
cascade with high-resolution hybrid-kinetic simulations of freely-decaying
turbulence in 3D3V phase space, including electron inertia effects. Two proton
plasma beta are explored: the "intermediate" and "low"
regimes, both typically observed in solar wind and corona. The
magnetic energy spectum exhibits and power laws
at , while they are slightly steeper at . Nevertheless,
both regimes develop a spectral anisotropy consistent with at , and pronounced small-scale intermittency.
In this context, we find that the kinetic-scale cascade is dominated by
KAW-like fluctuations at , whereas the low- case presents a
more complex scenario suggesting the simultaneous presence of different types
of fluctuations. In both regimes, however, a non-negligible role of ion
Bernstein type of fluctuations at the smallest scales seems to emerge.Comment: 6 pages, 5 figures, final version published in The Astrophysical
Journal Letters: Cerri, Servidio & Califano, ApJL 846, L18 (2017
Pressure anisotropy generation in a magnetized plasma configuration with a shear flow velocity
The nonlinear evolution of the Kelvin Helmholtz instability in a magnetized
plasma with a perpendicular flow close to, or in, the supermagnetosonic regime
can produce a significant parallel-to-perpendicular pressure anisotropy. This
anisotropy, localized inside the flow shear region, can make the configuration
unstable either to the mirror or to the firehose instability and, in general,
can affect the development of the KHI. The interface between the solar wind and
the Earth's magnetospheric plasma at the magnetospheric equatorial flanks
provides a relevant setting for the development of this complex nonlinear
dynamics.Comment: 11 pages, 7 figures, submitted to Plasma Phys. Control. Fusio
Plasma turbulence at ion scales: a comparison between PIC and Eulerian hybrid-kinetic approaches
Kinetic-range turbulence in magnetized plasmas and, in particular, in the
context of solar-wind turbulence has been extensively investigated over the
past decades via numerical simulations. Among others, one of the widely adopted
reduced plasma model is the so-called hybrid-kinetic model, where the ions are
fully kinetic and the electrons are treated as a neutralizing (inertial or
massless) fluid. Within the same model, different numerical methods and/or
approaches to turbulence development have been employed. In the present work,
we present a comparison between two-dimensional hybrid-kinetic simulations of
plasma turbulence obtained with two complementary approaches spanning about two
decades in wavenumber - from MHD inertial range to scales well below the ion
gyroradius - with a state-of-the-art accuracy. One approach employs hybrid
particle-in-cell (HPIC) simulations of freely-decaying Alfv\'enic turbulence,
whereas the other consists of Eulerian hybrid Vlasov-Maxwell (HVM) simulations
of turbulence continuously driven with partially-compressible large-scale
fluctuations. Despite the completely different initialization and
injection/drive at large scales, the same properties of turbulent fluctuations
at are observed. The system indeed self-consistently
"reprocesses" the turbulent fluctuations while they are cascading towards
smaller and smaller scales, in a way which actually depends on the plasma beta
parameter. Small-scale turbulence has been found to be mainly populated by
kinetic Alfv\'en wave (KAW) fluctuations for , whereas KAW
fluctuations are only sub-dominant for low-.Comment: 18 pages, 4 figures, accepted for publication in J. Plasma Phys.
(Collection: "The Vlasov equation: from space to laboratory plasma physics"
Finite-Larmor-radius equilibrium and currents of the Earth's flank magnetopause
We consider the one-dimensional equilibrium problem of a shear-flow boundary
layer within an "extended Hall-MHD" (eHMHD) model of plasma that retains
first-order finite Larmor radius (FLR) corrections to the ion dynamics. We
provide a generalized version of the analytic expressions for the equilibrium
configuration given in Cerri et al. (2013) [Cerri et al., Phys. Plasmas 20,
112112 (2013)], highlighting their intrinsic asymmetry due to the relative
orientation of the magnetic field and the
fluid vorticity
(" asymmetry"). Finally, we show that FLR effects can modify
the Chapman--Ferraro current layer at the flank magnetopause in a way that is
consistent with the observed structure reported by Haaland et al. (2014)
[Haaland et al., J. Geophys. Res. Space Phys. 119, 9019-9037 (2014)]. In
particular, we are able to qualitatively reproduce the following key features:
(i) the dusk-dawn asymmetry of the current layer, (ii) a double-peak feature in
the current profiles, and (iii) adjacent current sheets having thicknesses of
several ion Larmor radii and with different current directions.Comment: version accepted for publication in Journal of Plasma Physic
Subproton-scale cascades in solar wind turbulence: driven hybrid-kinetic simulations
A long-lasting debate in space plasma physics concerns the nature of
subproton-scale fluctuations in solar wind (SW) turbulence. Over the past
decade, a series of theoretical and observational studies were presented in
favor of either kinetic Alfv\'en wave (KAW) or whistler turbulence. Here, we
investigate numerically the nature of the subproton-scale turbulent cascade for
typical SW parameters by means of unprecedented high-resolution simulations of
forced hybrid-kinetic turbulence in two real-space and three velocity-space
dimensions. Our analysis suggests that small-scale turbulence in this model is
dominated by KAWs at and by magnetosonic/whistler fluctuations
at lower . The spectral properties of the turbulence appear to be in
good agreement with theoretical predictions. A tentative interpretation of this
result in terms of relative changes in the damping rates of the different waves
is also presented. Overall, the results raise interesting new questions about
the properties and variability of subproton-scale turbulence in the SW,
including its possible dependence on the plasma , and call for detailed
and extensive parametric explorations of driven kinetic turbulence in three
dimensions.Comment: 6 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
Identification of Long-lived Charged Particles using Time-Of-Flight Systems at the Upgraded LHC detectors
We study the impact of picosecond precision timing detection systems on the
LHC experiments' long-lived particle search program during the HL-LHC era. We
develop algorithms that allow us to reconstruct the mass of such charged
particles and perform particle identification using the time-of-flight
measurement. We investigate the reach for benchmark scenarios as a function of
the timing resolution, and find sensitivity improvement of up to a factor of
ten, depending on the new heavy particle mass.Comment: 20 pages, 13 figure
Collision-dependent power law scalings in 2D gyrokinetic turbulence
Nonlinear gyrokinetics provides a suitable framework to describe
short-wavelength turbulence in magnetized laboratory and astrophysical plasmas.
In the electrostatic limit, this system is known to exhibit a free energy
cascade towards small scales in (perpendicular) real and/or velocity space. The
dissipation of free energy is always due to collisions (no matter how weak the
collisionality), but may be spread out across a wide range of scales. Here, we
focus on freely-decaying 2D electrostatic turbulence on sub-ion-gyroradius
scales. An existing scaling theory for the turbulent cascade in the weakly
collisional limit is generalized to the moderately collisional regime. In this
context, non-universal power law scalings due to multiscale dissipation are
predicted, and this prediction is confirmed by means of direct numerical
simulations.Comment: 7 pages, 5 figures, accepted for publication in Physics of Plasma
Comparing persistence diagrams through complex vectors
The natural pseudo-distance of spaces endowed with filtering functions is
precious for shape classification and retrieval; its optimal estimate coming
from persistence diagrams is the bottleneck distance, which unfortunately
suffers from combinatorial explosion. A possible algebraic representation of
persistence diagrams is offered by complex polynomials; since far polynomials
represent far persistence diagrams, a fast comparison of the coefficient
vectors can reduce the size of the database to be classified by the bottleneck
distance. This article explores experimentally three transformations from
diagrams to polynomials and three distances between the complex vectors of
coefficients.Comment: 11 pages, 4 figures, 2 table
Dual phase-space cascades in 3D hybrid-Vlasov-Maxwell turbulence
To explain energy dissipation via turbulence in collisionless, magnetized
plasmas, the existence of a dual real- and velocity-space cascade of
ion-entropy fluctuations below the ion gyroradius has been proposed. Such a
dual cascade, predicted by the gyrokinetic theory, has previously been observed
in gyrokinetic simulations of two-dimensional, electrostatic turbulence. For
the first time we show evidence for a dual phase-space cascade of ion-entropy
fluctuations in a three-dimensional simulation of hybrid-kinetic,
electromagnetic turbulence. Some of the scalings observed in the energy spectra
are consistent with a generalized theory for the cascade that accounts for the
spectral anisotropy of critically balanced, intermittent, sub-ion-Larmor-scale
fluctuations. The observed velocity-space cascade is also anisotropic with
respect to the magnetic-field direction, with linear phase mixing along
magnetic-field lines proceeding mainly at spatial scales above the ion
gyroradius and nonlinear phase mixing across magnetic-field lines proceeding at
perpendicular scales below the ion gyroradius. Such phase-space anisotropy
could be sought in heliospheric and magnetospheric data of solar-wind
turbulence and has far-reaching implications for the dissipation of turbulence
in weakly collisional astrophysical plasmas.Comment: version accepted in ApJ
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