This study presents a detailed investigation into the ion velocity distribution within the interconnected plume of a cluster of two coaxial Electron Cyclotron Resonance Thrusters (ECRTs), in what we denote as a magnetic arch configuration. Two-dimensional Laser-Induced Fluorescence (LIF) spectroscopy and electrostatic probes (Faraday cup, Langmuir probe and retarding potential analyser) are used. Spatially-resolved ion velocity vectors in the transversal plane of the cluster, as well as for a single ECRT, are obtained, with comparable velocity magnitudes (∼ 6.5 km/s) for both cases. In the case of the single source, the axial component of the velocity increases along the plume expansion. The radial component is null on the source centerline, and increases away from it. For the cluster, a MN-like expansion takes place on the outer side of the sources, while there is partial plasma confinement between the sources. Evidence of two distinct ion populations, coming from the two sources, could not be found. Along the cluster symmetry plane the ion density is ∼ 10 15 m -3 , whilst the electron temperature drops from 16 eV to 2 eV. We conclude that the closed-line topology of the magnetic arch topology of the cluster case partially traps ions, resulting in a decrease in terms of vz along with an increase of radial velocity around the cluster symmetry plane, but this does not prevent the extraction of a free plasma jet.