Differential kinetic dynamics and heating of ions in the turbulent solar wind

Abstract

The solar wind plasma is a fully ionized and turbulent gas ejected by the outer layers of the solar corona at very high speed, mainly composed by protons and electrons, with a small percentage of helium nuclei and a significantly lower abundance of heavier ions. Since particle collisions are practically negligible, the solar wind is typically not in a state of thermodynamic equilibrium. Such a complex system must be described through self-consistent and fully nonlinear models, taking into account its multi-species composition and turbulence. We use a kinetic hybrid Vlasov-Maxwell numerical code to reproduce the turbulent energy cascade down to ion kinetic scales, in typical conditions of the uncontaminated solar wind plasma, with the aim of exploring the differential kinetic dynamics of the dominant ion species, namely protons and alpha particles. We show that the response of different species to the fluctuating electromagnetic fields is different. In particular, a significant differential heating of alphas with respect to protons is observed. Interestingly, the preferential heating process occurs in spatial regions nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Moreover, by feeding a simulator of a top-hat ion spectrometer with the output of the kinetic simulations, we show that measurements by such spectrometer planned on board the Turbulence Heating ObserveR (THOR mission), a candidate for the next M4 space mission of the European Space Agency, can provide detailed three-dimensional ion velocity distributions, highlighting important non-Maxwellian features. These results support the idea that future space missions will allow a deeper understanding of the physics of the interplanetary medium.

Proton–Proton Collisions in the Turbulent Solar Wind: Hybrid Boltzmann–Maxwell Simulations

“…The electric and magnetic spectra obtained in the two runs perfectly match, and reveal the typical features observed in solar-wind plasma. Indeed, similarly to previous numerical experiments Valentini et al 2016;Pezzi et al 2018a), an inertial-like range is observed, where the magnetic PSD recalls the Kolmogorov prediction (orange dashed-line) (Kolmogorov 1941), although a proper power-law scaling is not observed due to the limited size of the simulation domain. Around kd p ∼ 1, the usual spectral steepening is recovered (Leamon et al 1998).…”

Sign Singularity of the Local Energy Transfer in Space Plasma Turbulence

“…Multi-spacecraft and high resolution measurements in the solar wind and in the terrestrial magnetosphere [12,13] have provided evidence of such interconnection [14]. The increasing performance of numerical simulations has also allowed processes on several scales to be examined, and therefore to highlight their relationship [15][16][17][18][19][20][21][22][23][24]. Theoretical efforts are also being carried out in order to highlight the specific processes governing the energy exchange between ranges associated to different regimes [25][26][27].…”

Finite-Larmor-radius equilibrium and currents of the Earth’s flank magnetopause

“…Matthaeus & Lamkin 1986;Biskamp 2008;Servidio et al 2010Servidio et al , 2011Lazarian et al 2012;Karimabadi et al 2013a;Servidio et al 2015;Franci et al 2016;. In this context, currents and coherent structures are typically related to simultaneous enhancement of vorticity, kinetic activity, turbulent transfer and dissipation (e.g., Servidio et al 2012Servidio et al , 2014Karimabadi et al 2013b;Valentini et al 2014Valentini et al , 2016Wan et al 2015;Franci et al 2016;Parashar & Matthaeus 2016;Yang et al 2017;Grošelj et al 2017;Camporeale et al 2018;Sorriso-Valvo et al 2018). Furthermore, reconnection/structures have been recently proved to enhance/trigger the kinetic turbulent cascades in real space Franci et al 2017;Camporeale et al 2018) and also to be related to simultaneous velocity space cascades (Servidio et al 2017;Cerri et al 2018;Pezzi et al 2018).…”