Electron heat flux instabilities in coronal holes: Implications for ion heating

[1] There is growing evidence that the heating of the ions in solar coronal holes and the resulting generation of the fast solar wind is due to cyclotron-resonant damping of ion cyclotron waves. At the same time, the origin of these waves is not understood. In this paper, it is suggested that the waves in the proton cyclotron frequency range are generated by a plasma microinstability due to a heat flux coming from the Sun. A new view is used according to which heat flux is launched intermittently by small-scale reconnection events (nanoflares) at the coronal base. This allows the heat flux to be sporadically large enough to drive the instabilities, while at the same time satisfying the time-averaged energy requirements of the solar wind. It is shown that in a low-beta coronal plasma an electrostatic heat-flux instability has a comparable threshold and much greater growth rate than a shear Alfven heat flux instability. The implications of these instabilities for the ion heating in the coronal holes are discussed.