A new technique for identifying and distinguishing between ion heating mechanisms in solar wind plasma

Abstract:

There is strong evidence that local, non-thermal heating of ions seen in the solar corona extends into interplanetary space, beyond the orbit of Earth. Even with detailed and long duration observations of solar wind thermal plasma and electromagnetic fields, major questions related to this heating remain unresolved. What is the physical process responsible for this heating? Is the same mechanism acting in the corona and in the solar wind? Are there multiple heating mechanisms that act at different levels depending on local conditions such as plasma beta? A large hurdle to date in resolving these questions is that the various candidate heating mechanisms produce similar results (i.e. radial temperature profiles, ion velocity distribution functions) as an end state, and thus are difficult to distinguish between. Here a new analysis technique is presented to identify the relative role of three common categories of local ion heating mechanisms: interaction with current sheets generated by turbulent dissipation, resonance with ion cyclotron waves, and interaction with kinetic Alfven waves. By correlating variations of ions at specific energies and magnetic fluctuations at varying spatial scales we can distinguish between different wave dispersion relations within the plasma, or identify the lack of a dispersive relation altogether. This technique is applicable to existing observations on the DSCOVR spacecraft, and to future missions such as Solar Probe Plus or THOR.