Production of molecular sideband radioisotope beams at CERN-ISOLDE using a Helicon-type plasma ion source

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 RF 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 17CO+ with a HfO2 fibre target, and a more than 50-fold enhancement of the 10CO+ and 11CO+ yields with a nanostructured CaO target and an upgraded ion source prototype.