Characterization and optimization of a versatile laser and electron-impact ion source for radioactive ion beam production at ISOLDE and MEDICIS

This work describes the operating regime of the newly commissioned CERN-MEDICIS facility and reports on the first extracted ion beams. To achieve this milestone and to ensure that the facility is capable of meeting the performance requirements, simulation software is used to optimize the ion beam extraction, mass separation and transport. The MEDICIS mass separator, recovered from the LISOL facility, has been characterized and optimized for this application: laser-window installation, electromagnetic field mapping and assessment of mass resolving power amongst others. In the quest of improving the performance of the ISOLDE FEBIAD (VADIS) ion source, a study of the dependence of the ionization efficiency on the operational parameters has been performed. The role of the cathode temperature, anode voltage, ion source magnetic field and gas load have been investigated, leading to recommendations for the optimal operation of the ion source. The ionization efficiencies for magnesium, manganese, gallium, tin and mercury were measured, with values ranging from 1-21 % recorded. Particle-in-cell software was used to visualize the electrostatic field distribution within the VADIS and VADLIS and to perform ion tracking. By doing so, the VADLIS, which has been recently developed at ISOLDE for the application of element-selective laser ionization in the FEBIAD cavity, was modified for enhanced extraction of laser-ions. This modification allows for the recovery of the extraction capabilities of the VADLIS when operated in the so-called RILIS mode. The modified VADLIS prototype, presented here, was used for the production of laser-ionized 24Mg, 71Ga, 98Mo and 196Hg beams, both off-line and on-line. An efficiency improvement greater than a factor of two was achieved in all cases, although, for species exclusively laser-ionized inside the FEBIAD anode, a seven-fold increase in efficiency was measured.