arXiv subjects

Pablo S Moya

Publications and source records attributed to Pablo S Moya.

7 recordsLinked to original sources

arXiv2026

Non-thermal plasma density redistribution in planetary magnetospheres due to ion-cyclotron waves

Planetary magnetospheres exhibit diverse environments where Ultra-low frequency (ULF) pulsations induce nonlinear ponderomotive effects. Since suprathermal populations modeled by Kappa distributions are ubiquitous in these regions, their significant influence on the ponderomotive force (PF) induced by electromagnetic ion cyclotron (EMIC) waves must be accounted for. We investigate field-aligned plasma density redistribution driven by the PF of traveling EMIC waves across different planetary magnetospheres. We apply a generalized slow-time-scale force balance equation to model stationary density solutions in low-beta plasmas ($β\ll 1$) with isotropic Kappa distributions. To enable systematic comparison, wave modulation is described using the WKB approximation in a dipole magnetic field, neglecting first-order curvature effects. The plasma response varies significantly with magnetospheric parameters: decreasing the kappa parameter and increasing plasma beta counteract plasma accumulation towards the equator. In low-beta environments, non-thermal effects substantially reduce the nonlinear response to short-period pulsations, though preserving the qualitative behavior of Maxwellian models. Furthermore, we characterize how the critical parameter governing the phase transition between equatorial density minima and maxima depends on the specific combination of plasma beta, kappa, and L-shell. Our study demonstrates that non-thermal plasma properties are a governing factor in field-aligned density redistribution driven by ULF waves, highlighting the necessity of incorporating them to accurately model ponderomotive phenomena across multifaceted planetary magnetospheres.

physics.space-ph↗

arXiv2026

Quasi-linear approach of bi-Kappa distributed electrons with dynamic $κ$ parameter. EMEC instability

In recent years, significant progress has been made in the velocity-moment-based quasi-linear (QL) theory of waves and instabilities in plasmas with nonequilibrium velocity distributions (VDs) of the Kappa (or $κ$) type. However, the temporal variation of the parameter $κ$, which quantifies the presence of suprathermal particles, is not fully captured by such a QL analysis, and typically $κ$ remains constant during plasma dynamics. We propose a new QL modeling that goes beyond the limits of a previous approach, realistically assuming that the quasithermal core cannot evolve independently of energetic suprathermals. The case study is done on the electron-cyclotron (EMEC) instability generated by anisotropic bi-Kappa electrons with $A=T_\perp/T_\parallel > 1$ ($\parallel, \perp$ denoting directions with respect to the background magnetic field). The parameter $κ$ self-consistently varies through the QL equation of kurtosis (fourth-order moment) coupled with temporal variations of the temperature components, relaxing the constraint on the independence of the low-energy (core) electrons and suprathermal high-energy tails of VDs. The results refine and extend previous approaches. A clear distinction is made between regimes that lead to a decrease or an increase in the $κ$ parameter with saturation of the instability. What predominates is a decrease in $κ$, i.e., an excess of suprathermalization, which energizes suprathermal electrons due to self-generated wave fluctuations. Additionally, we found that VDs can evolve toward a quasi-Maxwellian shape (as $κ$ increases) primarily in regimes with low beta and initial kappa values greater than five. Instability-driven relaxation only partially resolves temperature anisotropy in bi-Kappa electron VDs, as wave fluctuations generally act to further energize suprathermal electrons.

physics.plasm-ph↗

arXiv2025

Electron scale magnetic holes generation driven by Whistler-to-Bernstein mode conversion in fully kinetic plasma turbulence

Magnetic holes (MHs) are coherent structures characterized by a strong and localized magnetic field amplitude dip, commonly observed in the solar wind and planetary magnetosheaths. These structures come in different sizes, from magnetohydrodynamic to kinetic scales. Magnetospheric Multiscale (MMS) observations have revealed electron scale MHs to be ubiquitous in the turbulent Earth's magnetosheath, potentially playing an important role in the energy cascade and dissipation. Despite abundant observations, the origin of electron scale MHs is still unclear and debated. In this work, we use fully kinetic simulations to investigate the role of plasma turbulence in generating electron scale MHs. We perform a fully kinetic simulation of freely decaying plasma turbulence, initialized with typical Earth's magnetosheath parameters. We find that electron scale MHs can be generated by turbulence via the following mechanism: first, large-scale turbulent velocity shears produce regions with high electron temperature anisotropy; these localized regions become unstable, generating oblique electron scale whistler waves; as they propagate over the inhomogeneous turbulent background, whistler fluctuations develop an electrostatic component, turning into Bernstein-like modes; the strong electrostatic fluctuations produce current filaments that merge into an electron scale current vortex; the resulting electron vortex locally reduces the magnetic field amplitude, finally evolving into an electron scale MH. We show that MHs generated by this mechanism have properties consistent with MMS observations and nontrivial kinetic features. We provide numerical evidence of a new electron scale MH generation mechanism, driven by turbulence. Our results have potential implications for understanding the formation and occurrence of electron scale MHs in turbulent environments, such as the Earth's magnetosheath.

physics.space-ph↗

arXiv2023

Ponderomotive forces in magnetized non-thermal space plasmas due to cyclotron waves

The ponderomotive force is involved in a variety of space plasmas phenomena which are characterized by the family of Kappa distributions. Therefore, evaluating these nonthermal effects in the ponderomotive force is required. The Washimi and Karpman ponderomotive interaction due to cyclotron waves is evaluated for different space conditions considering low-temperature magnetized plasmas described by an isotropic Kappa distribution and with a wave propagation parallel to the background magnetic field. We performed a brief analysis of the influence of the Kappa distribution in the dispersion relation for a low-temperature plasma expansion at the lowest order in which the thermal effects are appreciated without considering the damping characteristics of the wave. The different factors of the ponderomotive force are obtained and analyzed separately as a function of the wavenumber, the spectral index $κ$, and the plasma beta. We have found a relevant influence of the non-thermal effects in all the factors of the ponderomotive force for magnetized plasmas. The effect of the kappa distribution has been evaluated for a wide variety of space environments as the solar wind and the different regions of our magnetosphere where it has been found that these results can be relevant for the solar wind, the magnetosheath, the plasmasheet, and the polar cusps. We have also analyzed the role of the non-thermal effect in the induced Washimi and Karpman ponderomotive magnetization in the context of spatial plasmas and the total power radiated associated with it. We find that even for nearly cold magnetized plasmas and waves far from the resonances the effect of the kappa parameter in the ponderomotive force cannot be neglected. This suggests a significant role of the Kappa distribution in ponderomotive phenomena of space physics.

physics.plasm-ph↗

arXiv2023

Interplay Between Anisotropy- and Skewness-driven Whistler Instabilities in the Solar Wind under the Core-Strahlo model

Temperature anisotropy and field-aligned skewness are commonly observed non-thermal features in electron velocity distributions in the solar wind. These characteristics can act as a source of free energy to destabilize different electromagnetic wave modes, which may alter the plasma state through wave-particle interactions. Previous theoretical studies have mainly focused on analyzing these non-thermal features and self-generated instabilities individually. However, to obtain a more accurate and realistic understanding of kinetic processes in the solar wind, it is necessary to examine the interplay between these two energy sources. By means of linear kinetic theory, in this paper we investigate the excitation of the parallel-propagating whistler mode, when it is destabilized by electron populations exhibiting both temperature anisotropy and field-aligned strahl or skewness. To describe the solar wind electrons, we adopt the Core-Strahlo model as an alternative approach. This model offers the advantage of representing the suprathermal features of halo and strahl electrons, using a single skew-Kappa distribution already known as the strahlo population. Our findings show that when the electron strahlo exhibits an intrinsic temperature anisotropy, this suprathermal population becomes a stronger and more efficient source of free energy for destabilizing the whistler mode. This suggests a greater involvement of the anisotropic strahlo in processes conditioned by wave-particle interactions. Present results also suggest that the contribution of core anisotropy can be safely disregarded when assessing the importance of instabilities driven by the suprathermal population. This allows for a focused study, particularly regarding the regulation of electron heat flux in the solar wind.

astro-ph.SR↗

arXiv2022

Ponderomotive forces in unmagnetized plasmas described by Kappa distribution functions

The Washimi and Karpman ponderomotive interaction due to electromagnetic waves propagation is investigated for unmagnetized plasmas described by a isotropic Kappa distribution. We performed a brief analysis of the influence of the Kappa distribution in the dispersion relations for a low temperature plasma expansion at the lowest order in which the thermal effects are appreciated. The spatial and temporal factor of the ponderomotive force is obtained as a function of the wavenumber, the spectral index $κ$ and the ratio between the plasma thermal velocity and the speed of light. Our results show that for unmagnetized plasmas non-thermal effects are negligible for the spatial ponderomotive force when non-relativistic thermal velocities are considered. However, for unmagnetized plasmas the temporal factor of the ponderomotive force appears only due to the presence of suprathermal particles, with a clear dependence on the $κ$ index. We have also analysed the role of the non-thermal effect in the induced Washimi and Karpman ponderomotive magnetization and the total power radiated associated with it. We have also shown that the slowly varying induced ponderomotive magnetic field magnitude increases as the plasma moves away from thermal equilibrium.

physics.plasm-ph↗

arXiv2022

The role of O+ and He+ on the propagation of Kinetic Alfvén Waves in the Earth's inner magnetosphere

Interactions between plasma particles and electromagnetic waves play a crucial role in the dynamics and regulation of the state of space environments. From plasma physics theory, the characteristics of the waves and their interactions with the plasma strongly depend on the composition of the plasma, among other factors. In the case of the Earth's magnetosphere, the plasma is usually composed by electrons, protons, O+, and He+ ions, all with their particular properties and characteristics. Here, using plasma parameters relevant for the inner magnetosphere we study the dispersion properties of Kinetic Alfvén Waves (KAW) in a plasma composed by electrons, protons, He+ ions, and O+ ions. We show that heavy ions induce significant changes to the dispersion properties of KAW, such as polarization, compressibility, and electric-to-magnetic amplitude ratio, and therefore the propagation of Kinetic Alfvén Waves is highly determined by the relative abundance of He+ and O+ in the plasma. These results when discussed in the context of observations in the Earth's magnetosphere, suggest that for many types of studies based on theory and numerical simulations, the inclusion of heavy ions should be customary for realistic modeling of plasma phenomena in the inner magnetosphere or other space environments in which heavy ions can contribute with a substantial portion of the plasma such as planetary magnetospheres and comet plasma tails.

physics.space-ph↗