In order to account for the increasing demand for strong molecular beams for nuclear physics experiments at ISOLDE, a new radioactive ion source concept based on an RE discharge in a magnetized plasma was developed at CERN. Experimental studies at the ISOLDE offline separator show that the optimum conditions for CO+ and CO2+ ion production are given when the ion source is operated with He plasma, in line with expectations based on their electron impact ionization cross-sections. At optimum tuning, ionization efficiencies of 2.5% and 4% were measured for CO+ and Ar+, respectively. The capability of the Helicon ion source prototype for ISOL operation was evaluated during two online runs at the General Purpose Separator of CERN-ISOLDE, yielding the first observation of (CO+)-C-17 with a HfO2 fibre target, and a more than 50-fold enhancement of the (CO+)-C-10 and (CO+)-C-11 yields with a nanostructured CaO target and an upgraded ion source prototype. (C) 2013 Elsevier B.V. All rights reserved.