Addressing the Turbulent Heating Problem with a Novel Diagnostic Method
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Dr. Kristopher G. Klein
Postdoctoral Research Fellow
Climate and Space Science
University of Michigan
Identifying the mechanisms that drive the dissipation of turbulence, thereby heating the solar wind, is of significant importance to understanding the evolution of this hot, diffuse plasma as it is accelerated from the solar surface and expands through the heliosphere. A number of classes of mechanisms have been proposed which transfer energy between the electromagnetic fields and the ions and electrons, including resonant (e.g. Landau and cyclotron damping), stochastic, and intermittent (e.g. energization associated with current sheets and reconnection sites) mechanisms. We describe a novel method to trace this energy transfer using field-particle correlations constructed from single-point measurements of the type typically made in the solar wind. The velocity-dependent nature of the transfer will allow for improved characterization of mechanisms which act to damp the turbulent fluctuations and heat the plasma. A derivation of the correlation employed is outlined, following the form of the nonlinear field-particle interaction term in the Vlasov equation. The correlation is applied to increasingly complex plasma simulations, ranging from simple electrostatic to turbulent electromagnetic cases, revealing the nature of the energy transfer in each system. We finally consider the application of this method to spacecraft observations, including those from current (DSCOVR and MMS), future (Solar Probe Plus and Solar Orbiter), and proposed (THOR and IMAP) missions. The single-point nature of the method is ideally suited to in situ observations of space plasmas and will help in answering what acts to heat the solar wind.
Host: Dr. Joe Giacalone