Kinetic instabilities of the suprathermal populations in the solar wind S. M. Shaaban 1,2 , M. Lazar 1,3 , S. Poedts 1 , A. Elhanbaly 2 1 CmPA, K.U.Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium 2 CTP, Physics Department, Mansoura University, 35516 Mansoura, Egypt 3 Theoretische Physik IV, Ruhr-University Bochum, D-44780 Bochum, Germany Abstract The kinetic properties of space plasmas, like their temperature anisotropy and the re- sulting instabilities, are in general studied considering only the thermal (core) popula- tions. The implications of suprathermal (halo) populations is minimized or just ignored, despite the fact that their presence in the solar wind and planetary magnetospheres is per- manently reported by the observations for all species of plasma particles (electrons, pro- tons or heavier ions), and their kinetic energy density may be significant. Here we present the results of a preliminary (linear) study of the kinetic instabilities driven by interplay of core and suprathermal populations, when both these two populations exhibit temper- ature anisotropies. For conditions specific to space plasmas, the effects of suprathermal populations can be more important than those triggered by the core component. In dilute plasmas from space Coulomb collisions are rare and inefficient in the relaxation of kinetic anisotropies, but the anisotropy-driven instabilities should explain the limits of temperature anisotropy measured in the solar wind. 1. Introduction The in-situ measurements of the velocity distributions (VDs) of plasma particles in the solar wind reveal states out of thermal equilibrium determined by the presence of suprathermal (halo) populations and deviations from isotropy, e.g., temperature anisotropy T k 6= T ⊥ relative to the stationary magnetic field B 0 [1]. In the absence of collisions only the resulting instabilities are efficient in limiting the increase of anisotropy as predicted, for instance, by the expansion of the solar wind, T k > T ⊥ , or the magnetic field compression in shocks, T ⊥ > T k . Driven by anisotropic protons with A p = T ⊥ /T k > 1, the electromagnetic ion-cyclotron (EMIC) instability may interact resonantly with protons scattering them back to quasi-equilibrium state, and limiting their anisotropy. The EMIC instability is mainly studied using simplified VDs which minimize the effects of suprathermal populations [2] and leads to questionable results (see [3], and discussions in [4]). However, the instability is highly dependent on the shape of proton distribution [4, 5, 6] which has a dual structure in the solar wind, with a thermal core and a hotter suprathermal halo, see [7] and references therein. Here we present the results of a 43 rd EPS Conference on Plasma Physics P1.104