Alfvénic turbulence driven temperature anisotropies of thermal non-equilibrium ions

Abstract

Kasper et al. have found that solar-wind helium could be heated to be nearly 7 times hotter than hydrogen on average from the observation of the Wind spacecraft. The stochastic Fermi mechanism is employed to investigate this phenomenon via the ion-cyclotron resonant process (Kasper J. C. et al., Phys. Rev. Lett., 110 (2013) 091102). Due to strong ion cyclotron resonances caused by counterpropagating Alfvén waves, the helium could be thermalized to be 7 times hotter than hydrogen. In this paper, a new aspect, the non-resonant interaction between thermal non-equilibrium particles and turbulent Alfvén waves, is utilized to illustrate the above observation analytically and numerically. The result of our model is broadly consistent with the observational result. Additionally, this paper predicts that the various temperature anisotropies of ions may exist in the solar-wind core which different thermal non-equilibrium factors lead to. This work builds up a close relation among non-resonant heating of thermal non-equilibrium ions, differential flow, and temperature anisotropy.