Tools for Predicting the Rates of Turbulent Heating for Protons, Electrons, and Heavy Ions in the Solar Wind

In the parts of the solar corona and solar wind that experience the fewest Coulomb collisions, the various particle species (i.e., protons, electrons, and heavy ions) are not in thermal equilibrium with one another. The particles exhibit a range of different outflow speeds, temperatures, and velocity distribution anisotropies, and these differences can be used to probe the kinetic physical processes that are responsible for depositing energy into the plasma. In this presentation, we outline a new modeling framework for simulating the rates of collisionless heating for each species, in which the energy input is assumed to come from MHD turbulence. We begin by creating a one-dimensional model of damped wave action conservation for Alfven, fast-mode, and slow-mode MHD waves. This model provides the total wave power in each mode as a function of radial distance along an expanding solar wind flux tube. Next we solve a set of cascade advection-diffusion equations that give the time-steady Fourier wavenumber spectra at each distance. An approximate term for nonlinear mode coupling between the Alfven and fast-mode fluctuations is included. We find that for sufficiently high amplitudes of the fast-mode waves, there arises enough Alfven wave energy at high frequencies to excite the proton and ion cyclotron resonances and heat these particles in the direction perpendicular to the background magnetic field. Although results will be shown primarily for the plasma conditions in polar coronal holes that give rise to high-speed solar wind streams, the tools outlined above can be applied straightforwardly in other plasma environments as well.