Speaker
David Burgess
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.J401.pdf
Characterizing nonlinear processes in simulations of turbulent space
plasmas
D. Burgess, L. Franci, D. Trotta
School of Physics and Astronomy, Queen Mary University of London, London UK
Natural collisionless plasmas, such as the solar wind, can be characterized in terms of their
turbulence properties, which are often taken from a framework focused on universal properties,
such as power spectra with power law slopes. Improving data analysis (higher resolution and
multi-spacecraft) has led to a refined picture in which characteristic plasma scales play a role.
For example, recent observational work has concentrated on the transition from inertial, fluid-
like scales to scales where particle kinetic processes (either ion or electron) become relevant.
At the same time, this transition has been much studied with kinetic simulations which can cap-
ture important kinetic effects but which are large enough to cover some of the inertial range.
These simulations remind us that turbulence in a collisionless plasma has a complex network
of processes involving particle energization and magnetic field topology, such as magnetic re-
connection, kinetic instabilities and wave-particle interactions, as well as nonlinear wave-wave
processes. We present results from a number of hybrid PIC simulations (kinetic ions with elec-
tron fluid) of solar wind turbulence that illustrate various aspects of this complex system. Sim-
ulations of the relaxation of a system of multiple current sheets show turbulent-like behaviour
with forward and inverse cascade. However, detailed characterization of the intermittency and
topological evolution using cancellation analysis shows that the system does not attain a state
of fully developed turbulence. Simulations initialised with long wavelength Alfvénic fluctua-
tions develop many of the power law spectral features observed in the solar wind, and we show
examples of comparisons between such simulations and data. We also use the simulations to
understand the role of magnetic reconnection in the evolution of the turbulence, and its connec-
tion to intermittency. Finally, we discuss how the particle distribution can be characterised in
the turbulence in terms of diffusion (both classical and anomalous), and the fragmented energy
release sites associated with reconnection.
