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" $\beta_p=1$ and "low" $\beta_p=0.2$ regimes, both typically observed in solar wind and corona. The magnetic energy spectum exhibits $k_\perp^{-8/3}$ and $k_\|^{-7/2}$ power laws at $\beta_p=1$, while they are slightly steeper at $\beta_p=0.2$. Nevertheless, both regimes develop a spectral anisotropy consistent with $k_\|\sim k_\perp^{2/3}$ at $k_\perp\rho_p>1$, and pronounced small-scale intermittency. In this context, we find that the kinetic-scale cascade is dominated by KAW-like fluctuations at $\beta_p=1$, whereas the low-$\beta$ 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 $k_\perp\rho_i\gtrsim1$ 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 $\beta\geq1$, whereas KAW fluctuations are only sub-dominant for low-$\beta$.Comment: 18 pages, 4 figures, accepted for publication in J. Plasma Phys. (Collection: "The Vlasov equation: from space to laboratory plasma physics"

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

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 $\beta\gtrsim1$ and by magnetosonic/whistler fluctuations at lower $\beta$. 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 $\beta$, 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

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 $\mathbf{b}=\mathbf{B}/|\mathbf{B}|$ and the fluid vorticity $\mathbf{\omega}=\mathbf{\nabla}\times\mathbf{u}$ ("$\mathbf{\omega b}$ 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

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

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

Efeito da profundidade de colocação do tubo de rega gota-a-gota na uniformidade de rega e na eficiência do uso da água em tomate de indústria

RESUMO A influência da profundidade da colocação dos gotejadores na uniformidade de rega e na eficiência do uso da água foi avaliada, durante dois anos, num ensaio em “split-plot”, com quatro repetições, sendo o tratamento principal a profundidade de colocação do tubo de rega: à superfície do solo (P0), a 20 cm (PI) e a 40 cm (PII) e o secundário a cultivar: Brigade e H3044. Nos dois anos, o débito médio dos gotejadores foi semelhante nos diferentes tratamentos. Os coeficientes de uniformidade (CU) e de variação (CV) e a uniformidade de distribuição (UD), determinados após a colheita da cultura, não foram afectados pela profundidade de colocação do tubo, tendo variado respectivamente, entre 96,5 e 98,2%, 1,91 e 4,15% e 94,5 e 97,4%. A rega gota-a-gota subsuperficial, comparativamente com a superficial, contribuiu para o aumento da eficiência do uso da água (Produção comercial/ETa) em 14%, fundamentalmente devido a uma diminuição da ETa, na fase inicial da cultura