Sensitive test for ion-cyclotron resonant heating in the solar wind.

Plasma carrying a spectrum of counterpropagating field-aligned ion-cyclotron waves can strongly and preferentially heat ions through a stochastic Fermi mechanism. Such a process has been proposed to explain the extreme temperatures, temperature anisotropies, and speeds of ions in the solar corona and solar wind. We quantify how differential flow between ion species results in a Doppler shift in the wave spectrum that can prevent this strong heating.