  Electron injection at high Mach-number nonrelativistic perpendicular shocks
is studied here for parameters that are applicable to young SNR shocks. Using
high-resolution large-scale two-dimensional fully kinetic particle-in-cell
(PIC) simulations and tracing individual particles we in detail analyze the
shock surfing acceleration (SSA) of electrons at the leading edge of the shock
foot. The central question is to what degree the process can be captured in
2D3V simulations. We find that the energy gain in SSA always arises from the
electrostatic field of a Buneman wave. Electron energization is more efficient
in the out-of-plane orientation of the large-scale magnetic field because both
the phase speed and the amplitude of the waves are higher than for the in-plane
scenario. Also, a larger number of electrons is trapped by the waves compared
to the in-plane configuration. We conclude that significant modifications of
the simulation parameters are needed to reach the same level of SSA efficiency
as in simulations with out-of-plane magnetic field or 3D simulations.
