Kinetic Turbulence and Particle Transport in Astrophysical Plasmas

• Applicant: Dr. Felix Spanier
• Subject Area: Astrophysics and Astronomy
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 406991908

In astrophysical plasmas like the solar wind or the interstellar medium turbulence has been observed. This means that energy in the plasma is cascading from large scales to smaller scales. Up to now the low frequency part of the spectrum (i.e., below the proton gyrofrequency) has been considered. In this frequency range plasma turbulence can be described using magnetohydrodynamics theory and the turbulence models by Kolmogorov or Goldreich and Sridhar. A prerequisite for this approach is a fluid description for the plasma.Recent observations in the solar wind as performed by Cluster and MMS and future observations by the THOR mission will grant a more detailed insight into turbulence beyond the proton gyrofrequency. In that range kinetic effect in the plasma become relevant and fluid descriptions are no longer an option. It has not been possible from observations and theoretical considerations to find a detailed description of wave modes and structures presents in the kinetic regime.The current project aims at a better understanding of this regime: Using numerical simulations, it shall be investigated how turbulence evolves over even larger scales. The core problem here is that there is not a single simulation technique capable of capturing all wave number ranges. Some techniques do not describe the physics in every regime, while other would incur a too large numerical effort.The ansatz of this project is to couple different techniques in a way that a multiscale model can be derived from the simulations, which spans a range from MHD turbulence to smallest kinetic scales. The techniques to be used are MHD simulations, hybrid and particle-in-cell codes.The following problems shall be approached in this project:- What is the nature of turbulence beyond the proton gyrofrequency?- Which influence does kinetic turbulence have on the particle transport (especially of electrons)?The last question is very important in this project. Particle transport itself is not only scientifically interesting, but the application to space weather have also technical applications. In this project there will be a special focus on the transport of electrons. Since electrons resonate mostly with turbulence in the kinetic regime, there should be an observable difference to proton transport. It shall be investigated if electron transport can be used to probe turbulence.

• DFG Programme: Research Grants