Free energy available to microinstabilities in the solar wind

Abstract:

The transport of energy in the solar wind is a complicated process where competing mechanisms transfer energy back and forth between the charged particles that make up the plasma and the electric and magnetic fields that are generated by their motion. At small scales, microinstabilities driven by non-equilibrium features in the velocity distributions of the particles can play a large role in this transfer, potentially explaining the significant amount of power in high-frequency waves observed in the solar wind. However, it is an open question how much energy is truly available to drive these waves and eventually heat the plasma. In this work, we develop an ansatz to quantify the amount of free energy available to microinstabilities that can be used to heat the plasma, and compare this quantity to predictions for other dissipation mechanisms. We apply this metric to a number of electrostatic test cases, and plan to apply the metric to Parker Solar Probe observations of electron distributions and Langmuir waves, and ultimately to simulations and observations of electromagnetic instabilities, with appropriate modifications to account for the simultaneous action of multiple types of microinstabilities and sources of free energy.