Hybrid Formulation of Fully- and Gyrokinetic Hamiltonian Field Theory for Space and Laboratory Plasma

Abstract:

The understanding of the nature of energy dissipation in weakly collisional Solar Wind is still an ongoing endeavor and considered one of the major unsolved problems in space plasma physics. While much is known about the dynamics of plasma in macroscopic fluid scales, the scientific community is still gradually understanding how heating happens in the kinetic scale, more specifically on the sub ion and electron scales. This is mostly due to the fact that kinetic simulations are considerably more expensive than fluid simulations. In the present work, we aim at developing a hybrid model that computes fully kinetic ions, and gyrokinetic electrons. The reduced nature of the electrons description allow us to capture the kinetic effects believed to play a role in energy dissipation, namely electron landau damping, while we expect substantial savings in computing thanks to the reduced nature of the electron description, it still allows us to retain the kinetic effects of the ions.

More specifically, we make use of a geometrical reduction of the phase space Lagrangian for the electrons, at the same time keeping the fully kinetic ion formulation on the same heterogeneous manifold. We then use the variational principle in the hybrid Lagrangian, encapsulating fully kinetic ions and gyrokinetic electrons, to study electromagnetic turbulence at sub ion scales. From a numerical perspective, we analyze a linearized version of the system through a dispersion relation solver, and compare our results with a fully kinetic and a fluid solver. This work should allow us to investigate in more detail the nature of energy dissipation of weakly collisional plasmas both in space and laboratory plasmas, opening doors to a computationally feasible treatment of sub ion kinetic physics and its relationship to the cross-scale energy transfer.