Transit-Time Damping Signatures in Solar Wind Turbulence Simulations

Understanding the physical mechanisms of the damping of the turbulent fluctuations has broad applications to the study of many astrophysical plasmas. At the dissipation range, the in situ measurements bring particular challenges, for example, integration over a spatial volume is not possible with only data at a single point available for single spacecraft. The problem can be solved by employing the field-particle correlation (FPC) technique to isolate the secular energy transfer from turbulent electromagnetic fields to the plasma particles and track down the unique velocity-space signature for each physics process. Landau damping (LD) and transit-time damping (TTD) are both possible mechanisms. Previous work has revealed the velocity-space signature of LD. In this research, the key physics of TTD is extracted by working through the limit of the Vlasov-Maxwell dispersion relation. The velocity-space signature of TTD and the comparison with that of LD is demonstrated. The simulation code AstroGK is applied to carry out both linear and turbulent runs, and the examination of the simulated results illustrates the varied contributions of TTD under different initial settings. This work provides a detailed study of TTD and helps gain scientific insights into the turbulent damping.