  Magnetic reconnection has long been known to be the most important mechanism
as quick conversion of magnetic field energy into plasma kinetic energy. In
addition, energy dissipation by reconnection has gained attention not only as a
plasma heating mechanism, but also as a plasma mechanism for accelerating
nonthermal particles. However, the energy partitioning of thermal and
nonthermal plasmas during magnetic reconnection is not understood. Here, we
studied energy partition as a function of plasma sheet temperature and guide
magnetic field. In relativistic reconnection with anti-parallel magnetic field
or weak guide magnetic field, it was found that the nonthermal energy density
can occupy more than $90 \%$ of the total kinetic plasma energy density, but
strengthening the guide magnetic field suppresses the efficiency of the
nonthermal particle acceleration. In nonrelativistic reconnection for
anti-parallel magnetic field, most dissipated magnetic field energy is
converted into thermal plasma heating. For a weak guide magnetic field with a
moderate value, however, the nonthermal particle acceleration efficiency was
enhanced, but strengthening the guide-field beyond the moderate value
suppresses the efficiency.

High Energy Astrophysical Phenomena;Plasma Physics