Electron Heat Flux Instabilities in Coronal Holes: Implications for Ion Heating

We show that in a low-beta coronal hole plasma the electrostatic ion cyclotron instability driven by an electron heat flux can have a larger growth rate and a lower threshold than shear Alfven, magnetosonic, and whistler instabilities, with the most competitive instability being the shear Alfven instability. We will discuss the implications of this result for the heating of protons and heavier ions in coronal holes. To model the electron heat flux, we use a three-component plasma consisting of protons, core electrons, and halo electrons drifting with respect to each other. We consider distribution functions that are stable to higher-frequency and potentially faster-growing electron instabilities. We demonstrate that in this case the heat flux is sufficient to drive the ion cyclotron and shear Alfven instabilities with growth rates that are high enough to give significant heating of protons and heavy ions.