Suprathermal Population Research Articles

Dust ion-acoustic dromions in Saturn’s magnetosphere

ABSTRACTMotivated by observations of localized electrostatic wavepackets by the Cassini – and (earlier) by Voyager 1 and 2 – mission(s) in Saturn’s magnetosphere, we have investigated the existence conditions and the dynamical evolution of localized multidimensional structures in the Saturnian dusty plasma environment. To this effect, we have adopted a plasma-fluid model for dust-ion acoustic excitations, taking into account the presence of a highly energetic (suprathermal, kappa-distributed) electron population in combination with massive dust dust particulates in the background. A multiple scales perturbation method was shown to lead to a Davey--Stewartson (DS) system of evolution equations, if one assumes perpendicular carrier wave propagation across the magnetic field (direction). The system is then shown to possess two regimes mainly, known in the literature as DS-I and DS-II. In the former case, if certain conditions are fulfilled, exponentially localized solutions are obtained, known as dromions. The combined effects of various physical parameters, such as the electron spectral index, the ambient magnetic field (strength), and the dust concentration, have been examined. A numerical investigation reveals that the dromion amplitude increases with higher dust concentration, whereas it decreases for lower κe (i.e. with an increase in the suprathermal electron population component). A stronger magnetic field results in higher amplitude but narrower dromions. Our results provide a comprehensive framework for modeling modulated electrostatic wavepackets, in direct comparison with experimental data in planetary environments, in Saturn’s magnetosphere and elsewhere.

Retracted: New Types of Electron Pitch Angle Distributions on Mars: Funnel and Skirt Distributions

AbstractUsing high‐resolution Solar Wind Electron Analyzer data from the Mars Atmosphere and Volatile EvolutioN spacecraft, we report two new types of electron pitch angle distributions (PADs) in the Martian plasma environment. The first type of electron PADs, showing pitch angle primally around , is termed funnel distribution, which was observed near the terminator and at about 1,200 km altitude. The second type of electron PADs, showing pitch angle primally around , is termed skirt distribution, which was detected on the nightside and at about 1,250 km altitude. The electrons of funnel and skirt distributions do not exhibit any photoelectron signatures and are shown to originate from the solar wind. Through the fitting analysis, we find that the electrons showing both funnel and skirt PADs are thermal electron populations and suprathermal electron populations. In addition, the possibilities that such two types of electron pitch angle distributions corresponding to magnetic field configurations are also discussed.

Differential Behaviors of Suprathermal 4He and Fe Populations in the Interplanetary Medium during Solar Cycle 24

Investigations on the solar cycle variation of the properties of suprathermal populations (H and other heavy ions like 4He, 3He, C, O, and Fe) in the solar wind are sparse and hence poorly understood. In the present investigation, solar cycle variations of “quiet” time suprathermal elements are investigated using <∼ 1 MeV n−1 particle flux data obtained from the Ultra-Low Energy Isotope Spectrometer on board the Advanced Composition Explorer satellite during solar cycles 23 and 24. The analysis reveals that helium (4He) shows zero or positive lags with respect to sunspot numbers in solar cycle 23 while it shows zero or negative lag in solar cycle 24. On the contrary, although iron (Fe) shows a zero or positive lag in cycle 23 similar to 4He, it shows only a zero lag in cycle 24 and no negative lag is seen. Further, significant differences in the spectral indices are seen between 4He and Fe in cycle 24 compared to cycle 23. These results suggest that generation mechanisms responsible for suprathermal 4He and Fe underwent changes in cycle 24 and these mechanisms are probably dependent on the first ionization potential and mass-to-charge ratio. This proposition gets credence from the fact that changes in the lags and spectral slopes for C and O are not significantly different in cycles 23 and 24.

Solar Orbiter SWA Observations of Electron Strahl Properties Inside 1 AU

The Solar Wind Analyser (SWA) suite on Solar Orbiter includes an Electron Analyser System (SWA-EAS) which is capable of high temporal and angular resolution measurements of solar wind electrons in the energy range ∼1 eV to ∼5 keV. In this article we report early nominal phase observations of the suprathermal electron population at energies ≥70 eV (representative of the ’strahl’ population), and use a simple fitting routine and classification system to determine the characteristics of the distributions and determine the variations in their properties as a function of heliocentric distance and solar wind properties. We find that under our classification system a significant population of radially outward moving strahl beams is identifiable in the tested samples. These are seen in across solar wind speed regimes, but, consistent with earlier observations, are slightly more prevalent in high speed wind. These beams occur at all distances examined (∼0.43 to ∼1.0 AU), but do not show significant evolution with distance, suggesting a balance between focusing and scattering processes across the distance range covered. However, the data suggests that the beams broaden on average with increasing magnetic field strength and narrow on average with increasing solar wind speed. We also identify a small population, occurring in sporadic clusters, which have deficits in phase space density in the sunward moving part of the electron distribution. These clusters occur across the distance range sampled and show some variations in average properties with radial distance, suggesting they too are influenced by competing scattering and (de-)focusing processes. The implications for the origin and evolution of these electron populations derived from these new observations are explored.

Switchbacks in the Young Solar Wind: Electron Evolution Observed inside Switchbacks between 0.125 au and 0.25 au

Switchbacks are localized deviations from the nominal Parker spiral field in the solar wind. In this study, we investigate the electron distributions inside switchbacks, focusing primarily on the suprathermal (halo and strahl) populations. We explore electron parameters in relation to the angle of rotation of the magnetic field from radial to determine whether electron distributions observed within switchbacks have any differences from those outside of switchbacks. Our observations reveal several trends in the suprathermal electron populations inside switchbacks. We find that the sunward deficit in the electron velocity distribution function typically observed near the Sun is filled in at larger rotation angles. This results in the suprathermal electron density and heat flux in the antistrahl direction changing from a negative to a positive value. On many days, we also observe a positive correlation between the halo density and rotation angle, and this may suggest that the growth of the halo may fill in the sunward deficit. We also find that strahl distributions have an increased average angular spread at large magnetic field rotation angles. The increase in suprathermal electron flux in the antistrahl direction, and the increase in strahl width, together could suggest that enhanced scattering occurs inside switchbacks. Electron core beta values tend to increase with the magnetic field rotation angle, mainly due to a decrease in magnetic pressure. An increase in electron beta may favor the growth of instabilities inside switchbacks. The Parker Solar Probe observations therefore support an enhanced role for wave–particle interactions in switchbacks.

The properties of 0.11 keV–344 MeV ion spectra in the inner heliosheath using regularizedκ-distributions

Context.The shape of the ion energy spectra plays a critical role in determining the ion energetics, the acceleration mechanisms, and the possible sources of different plasma and suprathermal ion populations. The determination of the exact shape of the total particle spectrum provides the necessary means to address the inner heliosheath dynamics. Apart from various modelling efforts, a direct fit to the measured ion spectra for an extended energy range of ∼0.11–344 MeV has not been performed to date.Aims.We use an extended set of combined 0.11–55 keV remotely sensed energetic neutral atoms (ENA) measurements from the Interstellar Boundary Explorer (IBEX-Lo and IBEX-Hi) and the Cassini/Ion and Neutral Camera (INCA), converted to protons, together with ∼28 keV–344 MeV in situ ion measurements from the low-energy charged particle (LECP) and cosmic ray subsystem (CRS) experiments on Voyager 2, over the declining phase of solar cycle 23 (SC23) and the ascending phase of solar cycle 24 (SC24) to study the characteristics of the particle energy spectrum.Methods.We fitted the 0.11 keV–344 MeV composite ion spectra with a set of regularized isotropicκ-distribution functions (RKDs), which allowed us to determine the macroscopic physical properties.Results.We demonstrate that the 2009–2012 composite spectrum that corresponds to the declining phase of SC23 is well fitted by three different RKDs, while the 2013–2016 spectrum, associated with the rise of SC24, can only be approximated with six differentκ-distribution functions.Conclusions.Our results are generally consistent with shock accelerated particles that undergo additional acceleration inside the inner heliosheath. We identify a low-energy transmitted population of particles, a suprathermal reflected population and a very-high-energy component that is modulated by galactic cosmic rays. The 2013–2016 time period is most likely associated with a mixture of particles from SC23 and SC24, which is reflected by the need to employ six RDKs.

On the Kinetic Theory of Subauroral Arcs

AbstractWe report on a novel scenario of subauroral arcs within strong subauroral ion drifts (SAID)‐STEVE and Picket Fence. Their explanation requires a local source of low‐energy, ε &lt; 18.75 eV, suprathermal electrons, and N2 vibrational and electronic excitation below ∼270 km. We show that the ionospheric feedback instability in strong SAID flows with depleted density troughs generates intense, small‐scale field‐aligned currents and parallel electric fields below the F2 peak. With these fields, we employed a rigorous numerical solution of the Boltzmann kinetic equation for the distribution of ionospheric electrons and determined the power going to excitation and ionization of neutral gas (the energy balance). The obtained suprathermal electron population and energy balance at altitudes of ∼130–140 km are just what is necessary for Picket Fence. Concerning STEVE, the kinetic theory predictions are in a good qualitative agreement with its basic features, such as the enhanced continuum emissions. Besides, the theory predicts that subauroral arcs might have the transient phase with typical aurora‐like emissions that fade out afterward.

First Intrashot Observation of Runaway-Electron-Driven Instabilities at the Lower-Hybrid Frequency Range under ITER-Relevant Plasma-Wave Dispersion Conditions.

Kinetic instabilities driven by runaway electrons (REs) have recently received attention in the fusion community as a means to control and diagnose REs in a tokamak. Experiments aimed at studying such kinetic instabilities have been performed at the Frascati Tokamak Upgrade (FTU), where different families of waves have been identified, from wide-band bursting emissions to quasi-monochromatic waves and sharp lines, in the presence of REs with energies from a few to tens of MeV. A specific family of waves with intense kinetic drive was directly observed for the first time, during both the early Ohmic plasma start-up and the current ramp-up. A clear wave frequency scaling with respect to the electron density was demonstrated. This scaling, with the complementary analysis of signals observed at different magnetic fields, allowed the identification of these instabilities as lower-hybrid waves. The relevant analysis shown in this Letter is based on a continuous intrashot detection of the RE-driven wave, which is reported for the first time for this kind of instability. We demonstrated that unstable waves are excited already at the very beginning of a tokamak discharge, opening the way to new possible research on the exploitation of this kind of measurement for monitoring seed REs formation at the early plasma stage, while most diagnostics still have limited capabilities. The conditions for plasma wave dispersion at the early phase of the FTU discharge are very similar to the ones expected during the ITER start-up, when analogous instabilities might, hence, come to light, in case of formation of suprathermal populations.

Revisiting Ulysses electron data with a triple fit of velocity distributions

Context. Given their uniqueness, the Ulysses data can still provide us with valuable new clues about the properties of plasma populations in the solar wind, and especially about their variations with heliographic coordinates. In the context of kinetic waves and instabilities in the solar wind plasma, the electron temperature anisotropy plays a crucial role. To date, two electron populations (the core and the halo) have been surveyed using anisotropic fitting models, limited in general to the ecliptic observations. Aims. We revisit the electron data reported by the SWOOPS instrument on board the Ulysses spacecraft between 1990 and early 2008. These observations reveal velocity distributions out of thermal equilibrium, with anisotropies (e.g., parallel drifts and/or different temperatures, parallel and perpendicular to the background magnetic field), and quasi-thermal and suprathermal populations with different properties. Methods. We apply a 2D non-linear least squares fitting procedure, using the Levenberg–Marquardt algorithm, to simultaneously fit the velocity electron data (up to a few keV) with a triple model combining three distinct populations: the more central quasi-thermal core, the suprathermal halo, and a second suprathermal population consisting mainly of the electron strahl (or beaming population with a major field-aligned drift). The recently introduced κ-cookbook is used to describe each component with the following anisotropic distribution functions (recipes): Maxwellian distribution, regularized κ-distribution, and generalized κ-distribution. Most relevant are triple combinations selected as best fits (BFs) with minimum relative errors and standard deviations. Results. The number of BFs obtained for each fitting combination is 80.6% of the total number of events (70.7% in the absence of coronal mass ejections). Showing the distribution of the BFs for the entire data set, during the whole interval of time, enables us to identify the most representative fitting combinations associated with either fast or slow winds, and different phases of solar activity. The temperature anisotropy quantified by the best fits is considered a case study of the main parameters characterizing electron populations. By comparison to the core, both suprathermal populations exhibit higher temperature anisotropies, which slightly increase with the energy of electrons. Moreover, these anisotropies manifest different dependences on the solar wind speed and heliographic coordinates, and are highly conditioned by the fitting model. Conclusions. These results demonstrate that the characterization of plasma particles is highly dependent on the fitting models and their combinations, and this method must be considered with caution. However, the multi-distribution function fitting of velocity distributions has a significant potential to advance our understanding of solar wind kinetics and deserves further quantitative analyses.

Implications of Kappa Suprathermal Halo of the Solar Wind Electrons

The electron velocity distributions measured in-situ in space plasmas reveal two central populations, a low-energy and highly dense (quasi-)thermal core, and a more diffuse but hotter suprathermal halo. Even if the core contributes much more to the total number density than the suprathermal particles, the energetic electrons play an important role in the higher moments. Using a dataset of more than 120,000 solar wind observations of electron distributions, measured in the ecliptic between 0.35 and 3.3 AU, we investigate here the main characteristics of the halo population and its potential influence on the core, and macroscopic properties of electrons, i.e., number density (n), bulk velocity (u), temperature (T) and temperature anisotropy (T⊥/Τ//). The analysis indicates that the parameters exhibit interdependence trends characterized by correlations between certain of these parameters and the kappa exponent (κ) corresponding to the power law of the halo population tail. The links between low kappa and low number densities (of both the core and halo populations) confirm that Coulomb collisions can be quite ineffective even at low radial distances if the density of the plasma is sufficiently low. Moreover, halo populations with lower values of κ are also associated to higher temperature anisotropies, and to higher bulk velocity. An interdependence between core and halo populations is also suggested by an apparent (inverse) correlation between their density and temperature ratios. We further show relations between the parameters fitting the sum of a Maxwellian core and a Kappa halo, and those of a global (single) Kappa fit that incorporates both the core and halo components. Such a global Kappa is used in an exospheric model of the solar wind, to predict the influence of suprathermal electrons on the characteristics of the solar wind. These results should stimulate future detailed analysis of these relationships and correlations, which may contribute to a realistic modeling of the solar wind and the formation and evolution of suprathermal populations.

Is the Solar Wind Electron Strahl a Seed Population for the Earth’s Electron Radiation Belt?

1) Since the outer electron radiation belt is lost on occasion, the radiation belt needs seed electrons to rebuild. 2) The clear candidate for that seed population is energetic substorm-injected electrons in the dipolar magnetosphere. 3) The energetic substorm-injected electrons in the dipole come from the suprathermal electron population in the magnetotail plasma sheet, delivered by substorms. Scenario (1)–3) begs the question: Where do these magnetotail suprathermal electrons come from? We are hypothesizing that one source (perhaps the dominant source) is the energetic field-aligned electron strahl in the solar wind, which are electrons fresh from the solar corona.

Toward a Realistic Evaluation of Transport Coefficients in Non-equilibrium Space Plasmas

Abstract Recent studies have outlined the interest for the evaluation of transport coefficients in space plasmas, where the observed velocity distributions of plasma particles are conditioned not only by the binary collisions, e.g., at low energies, but also by the energization of particles from their interaction with wave turbulence and fluctuations, generating the suprathermal kappa-distributed populations. This paper provides a first estimate of the main transport coefficients based on regularized kappa distributions, which, unlike standard kappa distributions (SKDs), enable macroscopic parameterization without mathematical divergences or physical inconsistencies. All transport coefficients derived here, i.e., the diffusion and mobility coefficients, electric conductivity, thermoelectric coefficient, and thermal conductivity, are finite and well defined for all values of κ &gt; 0. Moreover, for low values of κ (i.e., below the SKD poles), the transport coefficients can be orders of magnitudes higher than the corresponding Maxwellian limits, meaning that significant underestimations can be made if suprathermal electrons are ignored.

Simulation of Proton Acceleration With Varying Laser Intensity in the Presence of Suprathermal Electrons

In the framework of high laser–plasma interaction, 1-D particle-in-cell (PIC) simulations are performed in order to optimize the role of electron suprathermality to generate high-quality proton beams useful for diverse applications, despite the presence of high nonlinear laser effects. For that, the electrons are supposed to obey the kappa distribution function discretized in the simulation code. Various characteristics of the proton beams, such as proton and electron densities, electric fields, front position, and energy spectra, have been analyzed as functions of electron suprathermality and laser amplitude. It is shown that, in the case of the presence of an important population of suprathermal electrons, the protons converge toward the same energy, leading to a quasi-monoenergetic beam and to good front position stability despite the presence of a large laser field. In addition, the two effects of electron suprathermality and laser intensity are added to enhance the proton acceleration. It turns out that in the analyzed range of laser intensities, the presence of the suprathermal electron population is beneficial for the proton acceleration process, which minimizes the nonlinear effects due to the laser field induced in high laser–plasma acceleration.

Temperature Anisotropy Instabilities Stimulated by the Solar Wind Suprathermal Populations

This review paper compiles recent results obtained by the present group of authors describing the effects of suprathermal populations present in space plasmas (up to a few keVs) on temperature anisotropy instabilities. Of particular interest are the electromagnetic cyclotron and firehose excitations, which play a major role in limiting temperature anisotropy, resulting, for instance, from the adiabatic expansion of the solar wind. Relying on a rigorous modeling and interpretation of the observed velocity distributions, both theoretical models and numerical simulations indicate a systematic stimulation of these excitations in the presence of suprathermal populations of electrons or protons. Moreover, the enhanced fluctuations react back on particles, and determine a faster and deeper relaxation of their anisotropy. The present comparative analysis suggests that previous studies, considering only quasi-thermal low-energy populations, may have significantly underestimated these excitations and their implications in various applications in space plasmas.

MMS Observations of Super Thin Electron‐Scale Current Sheets in the Earth's Magnetotail

AbstractFlapping of the current sheet (CS) associated with the propagation of high‐velocity bulk flows allowed to observe the super thin current sheet (STCS) in the magnetotail plasma sheet (PS). During the interval of interest, 111 crossings of the CS neutral plane were detected. In 95 crossings, the STCSs with a current density J ≥ 20 nA/m2 were observed. A half‐thickness (LSTCS) of the STCSs was about a few electron gyroradii or less. In a number of the STCSs the parameter of adiabaticity (κe) was &lt;1.0 for suprathermal electron population (&gt;1 keV). Our analysis has shown that the electric current in such STCSs is carried by unmagnetized electrons (κe &lt; 1), and the stress balance is supported by the off‐diagonal terms of their pressure tensor. In this sense, the underlying physics of the formation of STCSs at electron scales by unmagnetized electrons is similar to the mechanism of ion‐scale thin CS formation by the quasi‐adiabatic ions. The low‐energy population of magnetized electrons is also crucially important since it keeps the STCS stable and allows their observation as a quasi‐stationary structure. We compare the observed half‐thickness of the STCS with that predicted by a new kinetic theory (λ) considering the coupling between ion‐scale TCS and electron‐scale STCS. We found a reasonable agreement between both values: LSTCS ∼ (0.3–1)λ. Further improvement in the theory taking into account the dynamics of unmagnetized electrons may provide better agreement with observations.

Elevation of runaway electron current by electron cyclotron resonance heating during disruptions on J-TEXT

Runaway electrons represent a serious problem for the reliable operation of future tokamaks. Radio frequency (RF) auxiliary heating can help suppress runaway electrons in the flat-top phase through a reduction in loop voltage. However, if a disruption occurs during RF auxiliary heating, it may lead to an increase in the runaway electron production due to the generation of a suprathermal population with energies in the order of ∼100 keV. The elevation of runaway current during disruptions by electron cyclotron resonance heating (ECRH) has been investigated on the J-TEXT tokamak. The results show that the conversion efficiency of runaway current increases with increased ECRH power. When the applied ECRH power is at the level of 400 kW, the conversion efficiency of Ohmic to runaway current increases from 35% to 75%, the thermal quench duration is decreased from 0.24 ms to 0.11 ms, and the Absolute Extreme Ultraviolet Spectrometer (AXUV) radiative power and electron density are about two times higher than the cases without ECRH heating.

Transport coefficients enhanced by suprathermal particles in nonequilibrium heliospheric plasmas

Context.In heliospheric plasmas, such as the solar wind and planetary magnetospheres, the transport of energy and particles is governed by various fluxes (e.g., heat flux, particle flux, current flow) triggered by different forces, electromagnetic fields, and gradients in density or temperature. In the outer corona and at relatively low heliocentric distances in the solar wind (i.e., &lt; 1 AU), particle-particle collisions play an important role in the transport of energy, momentum, and matter, described within classical transport theory by the transport coefficients, which relate the fluxes to their sources.Aims.The aim of the present paper is to improve the evaluation of the main transport coefficients in such nonequilibrium plasmas, on the basis of an implicit realistic characterization of their particle velocity distributions, in accord with the in situ observations. Of particular interest is the presence of suprathermal populations and their influence on these transport coefficients.Methods.Using the Boltzmann transport equation and macroscopic laws for the energy and particle fluxes, we derived transport coefficients, namely, electric conductivity, thermoelectric coefficient, thermal conductivity, diffusion, and mobility coefficients. These are conditioned by the electrons, which are empirically well described by the Kappa distribution, with a nearly Maxwellian (quasi-thermal) core and power-law tails enhanced by the suprathermal population. Here we have adopted the original Kappa approach that has the ability to outline and quantify the contribution of suprathermal populations.Results.Without exception, the transport coefficients are found to be systematically and markedly enhanced in the presence of suprathermal electrons (i.e., for finite values of theκparameter), due to the additional kinetic energy with which these populations contribute to the dynamics of space plasma systems. The present results also show how important an adequate Kappa modeling of suprathermal populations is, which is in contrast to other modified interpretations that underestimate the effects of these populations.

Hamiltonian kinetic-Hall magnetohydrodynamics with fluid and kinetic ions in the current and pressure coupling schemes

We present two generalized hybrid kinetic-Hall magnetohydrodynamics (MHD) models describing the interaction of a two-fluid bulk plasma, which consists of thermal ions and electrons, with energetic, suprathermal ion populations described by Vlasov dynamics. The dynamics of the thermal components are governed by standard fluid equations in the Hall MHD limit with the electron momentum equation providing an Ohm's law with Hall and electron pressure terms involving a gyrotropic electron pressure tensor. The coupling of the bulk, low-energy plasma with the energetic particle dynamics is accomplished through the current density (current coupling scheme; CCS) and the ion pressure tensor appearing in the momentum equation (pressure coupling scheme; PCS) in the first and the second model, respectively. The CCS is a generalization of two well-known models, because in the limit of vanishing energetic and thermal ion densities, we recover the standard Hall MHD and the hybrid kinetic-ions/fluid-electron model, respectively. This provides us with the capability to study in a continuous manner, the global impact of the energetic particles in a regime extending from vanishing to dominant energetic particle densities. The noncanonical Hamiltonian structures of the CCS and PCS, which can be exploited to study equilibrium and stability properties through the energy-Casimir variational principle, are identified. As a first application here, we derive a generalized Hall MHD Grad–Shafranov–Bernoulli system for translationally symmetric equilibria with anisotropic electron pressure and kinetic effects owing to the presence of energetic particles using the PCS.

On the distribution function of suprathermal particles at collisionless shocks

The departure of particle distributions from the Maxwellian is commonly observed in space plasmas. These non-Maxwellian distributions which are typical for plasmas that are not in thermal equilibrium, can be modeled with κ-distribution. Kinetic simulations of quasi-parallel collisionless shocks show that proton distribution is a composite of thermal, suprathermal, and non-thermal parts. By using particle-in-cell shock simulations, we show that κ-distribution adequately fits thermal and suprathermal parts together, as a single continuous distribution in early proton spectra. We derive suprathermal proton distribution directly from the generalized entropy of non-extensive statistical mechanics, and show that thermal and suprathermal populations are both naturally embedded in κ-distribution. We find that the index κ of the distribution increases with the distance from the shock, following the decrease in suprathermal part. The non-equilibrium plasma distribution which is continuously being enriched with suprathermal particles at the reforming shock barrier, reaches the thermal equilibrium in the far downstream. The suprathermal part completely fades there, and the shape of proton distribution becomes a Maxwellian from which directly emerges a power-law.

A New Low-beta Regime for Unstable Proton Firehose Modes in Bi-kappa-distributed Plasmas

Abstract In the solar-wind plasma an excess of kinetic temperature along the background magnetic field stimulates proton firehose modes to grow if the parallel plasma beta parameter is sufficiently high, i.e., β p∥ ≳ 1. This instability can prevent the expansion-driven anisotropy from increasing indefinitely and explain the observations. Moreover, such kinetic instabilities are expected to be even more effective in the presence of suprathermal Kappa-distributed populations, which are ubiquitous in the solar wind and are less affected by collisions than the core population but contribute with an additional free energy. In this work we use both linear and extended quasi-linear (QL) frameworks to characterize the unstable periodic proton firehose modes (propagating parallel to the magnetic field) under the influence of suprathermal protons. Linear theory predicts a systematic stimulation of the instability, suprathermals amplifying the growth rates and decreasing the instability thresholds to lower anisotropies and lower plasma betas (β p∥ &lt; 1). In perfect agreement with these results, the QL approach reveals a significant enhancement of the resulting electromagnetic fluctuations up to saturation with a stronger back reaction on protons, leading also to a faster and more efficient relaxation of the temperature anisotropy.