  The magnetic fields can change their topology through a process known as
magnetic reconnection. This process in not only important for understanding the
origin and evolution of the large-scale magnetic field, but is seen as a
possibly efficient particle accelerator producing cosmic rays mainly through
the first order Fermi process. In this work we study the properties of particle
acceleration in reconnection zones and show that the velocity component
parallel to the magnetic field of test particles inserted in nearly
non-resistive magnetohydrodynamic (MHD) domains of reconnection without
including kinetic effects, such as pressure anisotropy, the Hall term, or
anomalous effects, increases exponentially. Also, the acceleration of the
perpendicular component is always possible in such models. We have found that
within contracting magnetic islands or current sheets the particles accelerate
predominantly through the first order Fermi process, as previously described,
while outside the current sheets and islands the particles experience mostly
drift acceleration due to magnetic fields gradients. Considering two
dimensional MHD models without a guide field, we find that the parallel
acceleration stops at some level. This saturation effect is however removed in
the presence of an out-of-plane guide field or in three dimensional models.
Therefore, we stress the importance of the guide field and fully three
dimensional studies for a complete understanding of the process of particle
acceleration in astrophysical reconnection environments.
