  The primary focus of this paper is on the particle acceleration mechanism in
solar coronal three-dimensional reconnection null-point regions. Starting from
a potential field extrapolation of a Solar and Heliospheric Observatory (SOHO)
magnetogram taken on 2002 November 16, we first performed magnetohydrodynamics
(MHD) simulations with horizontal motions observed by SOHO applied to the
photospheric boundary of the computational box. After a build-up of electric
current in the fan-plane of the null-point, a sub-section of the evolved MHD
data was used as initial and boundary conditions for a kinetic particle-in-cell
model of the plasma. We find that sub-relativistic electron acceleration is
mainly driven by a systematic electric field in the current sheet. A
non-thermal population of electrons with a power-law distribution in energy
forms in the simulated pre-flare phase, featuring a power-law index of about
-1.78. This work provides a first step towards bridging the gap between
macroscopic scales on the order of hundreds of Mm and kinetic scales on the
order of cm in the solar corona, and explains how to achieve such a cross-scale
coupling by utilizing either physical modifications or (equivalent)
modifications of the constants of nature. With their exceptionally high
resolution - up to 135 billion particles and 3.5 billion grid cells of size
17.5 km - these simulations offer a new opportunity to study particle
acceleration in solar-like settings.
