We perform two-dimensional particle-in-cell simulations of magnetic
reconnection for various strengths of the guide field (perpendicular to the
reversing field), in magnetically-dominated electron-positron plasmas. Magnetic
reconnection under such conditions could operate in accretion disk coronae
around black holes. There, it has been suggested that the trans-relativistic
bulk motions of reconnection plasmoids containing inverse-Compton-cooled
electrons could Compton-upscatter soft photons to produce the observed
non-thermal hard X-rays. Our simulations are performed for magnetizations 3β€Οβ€40 (defined as the ratio of enthalpy density of the reversing
field to plasma enthalpy density) and guide field strengths 0β€Bgβ/B0ββ€1 (normalized to the reversing field strength B0β). We find that
the mean bulk energy of the reconnected plasma depends only weakly on the flow
magnetization but strongly on the guide field strength -- with Bgβ/B0β=1 yielding a mean bulk energy twice smaller than Bgβ/B0β=0.
Similarly, the dispersion of bulk motions around the mean -- a signature of
stochasticity in the plasmoid chain's motions -- is weakly dependent on
magnetization (for Οβ³10) but strongly dependent on the guide
field strength -- dropping by more than a factor of two from Bgβ/B0β=0 to Bgβ/B0β=1. In short, reconnection in strong guide fields
(Bgβ/B0ββΌ1) leads to slower and more ordered plasmoid bulk motions
than its weak guide field (Bgβ/B0ββΌ0) counterpart