Electron Heating in Magnetosheath Turbulence: Dominant Role of the
Parallel Electric Field within Coherent Structures
Abstract
How are particles being energized by turbulent electromagnetic fields is
an outstanding question in plasma physics and astrophysics. This paper
investigates the electron acceleration mechanism in strong turbulence
(δB/B0 ~ 1) in the Earth’s magnetosheath based on the
novel observations of the Magnetospheric Multiscale (MMS) mission. We
find that electrons are magnetized in turbulent fields for the majority
of the time. By directly calculating the electron acceleration rate from
Fermi, betatron mechanism, and parallel electric field, it is found that
electrons are primarily accelerated by the parallel electric field
within coherent structures. Moreover, the acceleration rate by parallel
electric fields increases as the spatial scale reduces, with the most
intense acceleration occurring over about one ion inertial length. This
study is an important step towards fully understanding the turbulent
energy dissipation in weakly collisional plasmas.