arXiv subjects

Roberto E. Navarro

Publications and source records attributed to Roberto E. Navarro.

5 recordsLinked to original sources

arXiv2026

The Effect of Expansion and Instabilities in the Thermodynamic Regulation of the Young Solar Wind Plasma

Using Parker Solar Probe measurements of the solar wind, we demonstrate that $β_{\parallel}$ is the main driver that determines which instabilities limit proton temperature anisotropy. At radial distances from 10 to 30 solar radii, $β_{\parallel}<1$ drives electromagnetic ion-cyclotron and parallel firehose instabilities, in contrast to the situation at 1 astronomical unit, where, due to most $β_{\parallel}>1$, mirror and oblique firehose modes are dominant instead. Furthermore, we show that the temperature anisotropy radially evolves following the semi-empirical anti-correlation $T_\perp/T_\parallel\simβ_\parallel^{-0.55}$, consistent with observations at larger distances from the Sun.

astro-ph.SR↗

arXiv2025

Proton-Acoustic Wave Effects on the Relaxation of Proton Transverse Heating in Magnetized Plasmas

Transverse electromagnetic and electrostatic plasma wave modes propagating along a background magnetic field $\vec{B}_0$ are independent according to linear kinetic theory. However, resonant interactions and energy exchange between waves and particles break this linear decoupling. This work tracks the coupled evolution of Alfvén-cyclotron (ACWs) and Ion-acoustic waves (IAWs) by solving moment-based quasilinear equations for a collisionless plasma of bi-Maxwellian protons and Maxwellian electrons. Unlike earlier quasilinear studies that adopt the cold-electron limit, our formulation retains the full kinetic response of both species, treating the electrons as a thermal reservoir to isolate proton heating. A parameter survey over $0.01\leqβ_{\parallel p}\leq10$ and $1\le T_e/T_p\le10$ shows that an ambient spectrum of ACWs can drive significant perpendicular proton heating and raise the temperature anisotropy from initially isotropic conditions at low $β_{\parallel p}\lesssim0.1$, thereby triggering cyclotron instabilities. The quasilinear evolution self-regulates the ACW, driving the system toward a quasi-stationary state with $γ/Ω_p<10^{-1}$ and reduced anisotropy. As $T_e/T_p$ increases, IAWs become less damped and absorb a larger share of the fluctuation energy through Landau resonance, reducing the efficiency of ACW-driven proton heating and thus regulating the instability. For sufficiently large $β_{\parallel p}$ or $T_e/T_p\gtrsim5$, ACWs become inefficient drivers of perpendicular heating, leaving IAWs as the dominant dissipation channel. These results explain how modest electrostatic activity in low-$β$ environments such as the inner heliosphere and planetary magnetosheaths can regulate, but not indefinitely sustain, cyclotron instabilities.

physics.plasm-ph↗

arXiv2025

Permutation Entropy for the Characterization of the Attractive Hamiltonian Mean-Field Model

The Hamiltonian Mean-Field (HMF) model is a long-range interaction model that exhibits quasi-stationary states associated with a phase transition. Its quasi-stationary states with a lifetime diverging with the number of particles in the system. These states are characterized by homogeneous or non-homogeneous structures in phase-space. There exists a phase-transition between these states that have been traditionally characterized by the their mean magnetization. However, the magnetization also exhibits fluctuations in time around its mean value, that can be an indicator of the kind of quasi-stationary state. Thus, we want to characterize the quasi-stationary states of the HMF model through the time-series of the magnetization and its fluctuations through a measure of information, i.e. the permutation entropy and the complexity-entropy plane. Permutation entropy is a measure for characterizing chaotic time series, especially in the presence of dynamic and observational noise, as it is computationally and conceptually simple. For non-homogeneous states, the permutation entropy shows that the HMF model tends towards order, while the magnetizacion fluctuations reveal reduced structures in time. On the contrary, homogeneous states tend to disorder and the structures of the magnetization fluctuations increase as the initial magnetization is larger. In all the study cases of this thesis, the HMF model is characterized by low entropy values but the highest possible complexity value. Thus, the HMF model can be described as a chaotic, deterministic and intermitent system. This aligns with previous studies of the model in the phase space. The results demonstrate that the HMF model can be understood and interpreted from the fluctuations of magnetization using permutation entropy and the complexity-entropy plane.

cond-mat.stat-mech↗

arXiv2022

Formation of Multiple Counter-propagating Clusters in the Attractive Hamiltonian Mean-field Model

Many-body long-range interacting systems can remain approximately in a quasi-stationary state far-from-thermodynamic equilibrium. These states are typically characterized by a pair of counter-propagating density clusters, or by a single non-homogeneous core-halo in the phase-space of the particles. By using particle simulations based on the Hamiltonian mean-field model, we show that this model supports stationary states with multiple cluster or particle holes in phase-space density. We also propose a mechanism based on wave-wave and wave-particle interactions that lead to the formation of these clusters, and characterize these new quasi-stationary states in terms of the initial parameters of the simulations.

nlin.PS↗

arXiv2021

Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas

Turbulence in space plasmas usually exhibits two regimes separated by a spectral break that divides the so called inertial and kinetic ranges. Large scale magnetic fluctuations are dominated by non-linear MHD wave-wave interactions following a -5/3 or -2 slope power-law spectrum. After the break, at scales in which kinetic effects take place, the magnetic spectrum follows a steeper power-law $k^{-α}$ shape given by a spectral index $α> 5/3$. Despite its ubiquitousness, the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures are usually not considered. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in an initially turbulent collisionless plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.

physics.plasm-ph↗