Rodrigo A. Lopez

Thermal electrons in Jupiter's magnetodisc have been observed to be anisotropic with higher parallel temperature compared to perpendicular. In this work, we used previously‐derived electron properties (Sarkango et al., 2025, https://doi.org/10.1029/2025gl118209 ) to calculate electron and compared the observed anisotropy with electron temperature‐anisotropy‐driven instability thresholds. For cold electrons, the ratio of perpendicular to parallel temperatures decreased with M‐shell, reached a minimum near M = 20–25, beyond which it increased until the distribution was quasi‐isotropic. In space, this turnover was observed close to the oblique electron firehose instability threshold. Linear dispersion analysis using plasma parameters representative of different M‐shells predicts the onset of the oblique firehose instability arising primarily due to cold electron anisotropy, though growth rates differ based on the cold and hot electron abundances, anisotropies, and . On the basis of these observations, we argue that the cold electron anisotropy in Jupiter's magnetodisc is regulated by the oblique electron firehose instability, which may be a source of plasma waves and could contribute to cyclotron‐resonant heating of the Jovian plasma.

Thermal electrons in Jupiter's magnetodisc have been observed to be anisotropic with higher parallel temperature compared to perpendicular. In this work, we used previously-derived electron properties (Sarkango et al. 2025) to calculate electron β _∥ and compared the observed anisotropy with electron temperature-anisotropy-driven instability thresholds. For cold electrons, the ratio of perpendicular to parallel temperatures (T _⊥ /T _∥ ) decreased with M-shell, reached a minimum near M=20-25, beyond which it increased until the distribution was quasi-isotropic. In T _⊥ /T _∥ -β _∥ space, this turnover was observed close to the oblique electron firehose instability threshold. Linear dispersion analysis using plasma parameters representative of different M-shells predicts the onset of the oblique firehose instability arising primarily due to cold electron anisotropy, though growth rates differ based on the cold and hot electron abundances, anisotropies, and β _∥ . On the basis of these observations, we argue that the cold electron anisotropy in Jupiter's magnetodisc is regulated by the oblique electron firehose instability, which may be a source of plasma waves and could contribute to cyclotron-resonant heating of the Jovian plasma.

Realistic modeling of type III solar radio bursts is essential for remotely diagnosing their exciters, the driving electron beams, and the ambient plasma. A new method is proposed to construct synthetic dynamic spectra of type III solar radio bursts, with frequency decreasing as a function of the distance or time traveled by their electron-beam plasma source in interplanetary space. This work introduces the first radio spectra computed from particle-in-cell (PIC) simulations within a dynamic model that is both quantitative and self-consistent, yet simplified by neglecting propagation effects (e.g., scattering and dissipation). Relevant to type III radio emissions, the input parameterization yields complex spectra that include the fundamental emission and the second and third harmonics, and thus determine a broadband consistent with that of the observations. These radio components are delimited and highlighted, enabling computations of their energy density on the basis of simulated first-principle mechanisms.

Thermal electrons in Jupiter's magnetodisc have been observed to be anisotropic with higher parallel temperature compared to perpendicular. In this work, we used previously-derived electron properties (Sarkango et al. 2025) to calculate electron β _∥ and compared the observed anisotropy with electron temperature-anisotropy-driven instability thresholds. For cold electrons, the ratio of perpendicular to parallel temperatures (T _⊥ /T _∥ ) decreased with M-shell, reached a minimum near M=20-25, beyond which it increased until the distribution was quasi-isotropic. In T _⊥ /T _∥ -β _∥ space, this turnover was observed close to the oblique electron firehose instability threshold. Linear dispersion analysis using plasma parameters representative of different M-shells predicts the onset of the oblique firehose instability arising primarily due to cold electron anisotropy, though growth rates differ based on the cold and hot electron abundances, anisotropies, and β _∥ . On the basis of these observations, we argue that the cold electron anisotropy in Jupiter's magnetodisc is regulated by the oblique electron firehose instability, which may be a source of plasma waves and could contribute to cyclotron-resonant heating of the Jovian plasma.

Parker Solar Probe observations in the young solar wind reveal new properties of both plasma particle velocity distributions (VDs) and associated electromagnetic (EM) wave fluctuations. The quasilinear (QL) kinetic theory of plasma wave instabilities has recently shown that new hammerhead (HH) proton distributions can be generated by the relaxation of proton beams through the instabilities of right-handed (RH) polarized waves. Such RH waves have indeed been reported in association with HH distributions. In this paper, new results from hybrid simulations of proton beam–plasma systems with properties typical of those observed to excite EM-RH wave instabilities are presented. From the long-term evolution of these systems, it is found that beam relaxation is driven by instabilities and growing wave fluctuations, leading to HH-type features in the VDs. The production of these features, as well as their prominence, depends on the magnetic power of the waves generated by the instabilities and, therefore, implicitly on the available free energy, quantified by the plasma beta parameter and the relative beam drift. The simulation results capture the self-consistent evolution of the instabilities and their nonlinear development. Linear theory, together with simulations, helps identify the nature of the unstable modes and the plasma conditions under which they arise. The good agreement with QL theory further indicates that it can serve as a computationally efficient complementary framework for interpreting the associated wave–particle interactions.

Context. Despite the fact that electrons observed in situ in space plasmas have three major components – the quasi-thermal core, suprathermal halo, and strahl – the analysis of instabilities triggered by kinetic, velocity-space anisotropies (such as relative drifts and temperature anisotropy) generally considers only two of these components. Aims. We aim to demonstrate that a realistic modeling with all three components is achievable in the present analysis focusing on heat-flux instabilities. In the absence of particle–particle collisions, these instabilities are responsible for the regulation of the heat flux carried mainly by suprathermal electrons. Methods. The velocity distributions of the electron populations were modeled according to in situ observations, with a Maxwellian core and Kappa-distributed halo and strahl components. We exploited new advanced numerical codes capable of solving the linear dispersion and stability properties of any plasma system with Maxwellian- and Kappa-distributed populations. Results. The unstable solutions differ significantly from those obtained with simplified models with only two components (such as core-strahl or core-beam models). The growth rates predict the systematic excitation and interplay of two unstable modes, whistler heat-flux and/or fire-hose heat-flux instabilities. The numerical solver “ALPS” was successfully applied to systems with regularized Kappa distributions, for which the analytical derivation of dispersion relations is not straightforward. Conclusions. The two instabilities are triggered by the two relative drifts, core-strahl and halo-strahl, and may have new consequences concerning the regulation of the heat flux. Particularly important are the cases when the core-strahl instability known from previous studies is in competition with the new instability driven by the halo-strahl drift, as well as when the two instabilities have the same nature and can accumulate. Future studies are thus motivated to confirm these predictions in quasilinear theories and numerical simulations.

Space plasmas are weakly collisional since characteristic timescales related to Coulomb collisions are much larger than those of Larmor gyration or wave–particle interactions. Thus, wave activity is likely to drive some of the nonthermal features that are observed in space plasma velocity distributions, such as temperature anisotropy, beams, and skewness. Therefore, we study how wave–particle interactions shape the velocity distribution functions of minor ions, and how these ions and their statistical properties modify the dispersion relation of electromagnetic waves. To achieve this, we derive the motion of heavy ions in electromagnetic waves using the Boris algorithm. We take the waves to be solutions of the fully kinetic dispersion relation of electromagnetic waves in two-ion component plasmas with parameters representative of solar wind. We use the Arbitrary Linear Plasma Solver code to derive the linear Vlasov–Maxwell dispersion relation based on the actual distribution of the ions. The test particles are initially in thermal equilibrium, and their distribution evolves due to interactions with the waves. By solving the dispersion relation using the evolved distributions, we show that the system evolves into a steady wave–particle equilibrium, which is characterized by a minimization of the interaction and energy transfer between waves and particles.

In recent years, significant progress has been made in the velocity-moment-based quasilinear (QL) theory of waves and instabilities in plasmas with non-equilibrium 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 (Moya et al. 2021), 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⊥/T∥ > 1 (∥, ⊥ 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 towards a quasi-Maxwellian shape (as κ increases) primarily in regimes with low beta and initial kappa values ≳ 5. The relaxation of bi-Kappa electron VDs under the action of instability is only partial by reducing the temperature anisotropy, whereas the contribution of wave fluctuations generally enhances suprathermal electrons. The present results show preliminary agreement with in-situ observations in the solar wind, suggesting that the new QL model could provide a sufficiently explanatory theoretical basis for the kinetic instabilities in natural plasmas with Kappa-like distributions.

Context. 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. Aims. 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. Methods. The case study is done on the electron-cyclotron (EMEC) instability generated by anisotropic bi-Kappa electrons with A = T _⊥ / T _∥ > 1 (∥, ⊥ 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. Results. 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. Conclusions. Instability-driven relaxation only partially resolves temperature anisotropy in bi-Kappa electron VDs, as wave fluctuations generally act to further energize suprathermal electrons. The present results show a preliminary agreement with in situ observations in the solar wind, suggesting that the new QL model could provide a sufficiently explanatory theoretical basis for the kinetic instabilities in natural plasmas with Kappa-like distributions.

In situ observations of the fast solar wind in the inner heliosphere show that minor ions and ion subpopulations often exhibit distinct drift velocities. Both alpha particles and proton beams stream at speeds that rarely exceed the local Alfvén speed relative to the core protons, suggesting the presence of instabilities that constrain their maximum drift. We aim to propose a mechanism that generates an alpha-particle beam through nonlinear Landau damping, primarily driven by the relative super-Alfvénic drift between protons and alpha particles. To investigate this process, we perform one-dimensional, fully kinetic particle-in-cell simulations of a nonequilibrium multispecies plasma complemented by its linear theory to validate the model during the linear phase. Our results provide clear evidence that the system evolves by producing an alpha-particle beam, thereby suggesting a local mechanism for alpha-beam generation via nonlinear Landau damping.