  The dynamics of a plasmoid chain is studied with three dimensional
Particle-in-Cell simulations. The evolution of the system with and without a
uniform guide field, whose strength is 1/3 the asymptotic magnetic field, is
investigated. The plasmoid chain forms by spontaneous magnetic reconnection:
the tearing instability rapidly disrupts the initial current sheet generating
several small-scale plasmoids, that rapidly grow in size coalescing and
kinking. The plasmoid kink is mainly driven by the coalescence process. It is
found that the presence of guide field strongly influences the evolution of the
plasmoid chain. Without a guide field, a main reconnection site dominates and
smaller reconnection regions are included in larger ones, leading to an
hierarchical structure of the plasmoid-dominated current sheet. On the contrary
in presence of a guide field, plasmoids have approximately the same size and
the hierarchical structure does not emerge, a strong core magnetic field
develops in the center of the plasmoid in the direction of the existing guide
field, and bump-on-tail instability, leading to the formation of electron
holes, is detected in proximity of the plasmoids.
