Generation of MHD turbulence by non-equilibrium ion velocity distributions in the outer heliosphere and the interstellar medium: magnetohydro-thermodynamic and kinetic views

Abstract

Abstract We show that energetic ions, appearing in plasmas due to injection of charge-exchange-induced new ions into the magnetized plasma background, flow due to their freely convertible energy drive turbulences of Alfvenic and magneto-acoustic types. This becomes important especially under conditions of strongly charge-exchanging fluids with supersonic differential bulk velocities, as is the condition in the inner heliosphere. These ion-driven waves lead to strongly enhanced fluctuation amplitudes. As a consequence, both low- and high-energy ion populations can partly reabsorb these wave energies, and thereby experience non-thermal heatings. As a quantitative example, we calculate the non-adiabatic behaviours of solar wind ions and pick-up ions expanding with the solar wind towards large solar distances. While pick-up ions behave nearly isothermal, normal solar wind ions behave pseudo-polytropically with negative effective polytropic indices that describe temperature increases at diverging plasma flows....