Abstract
Abstract The Versatile Arc Discharge and Laser Ion Source (VADLIS) is a recently established ion source for the CERN-ISOLDE radioactive ion beam facility. It offers either electron-impact ionization (VADIS-mode) or resonance laser ionization (RILIS-mode). The choice of operating mode depends on the element of interest or the required beam purity. Particle-in-cell simulations using the VSim software show that the ion extraction efficiency of the VADLIS in RILIS-mode can be improved if it is equipped with an insulated extractor plate, to which an optimal voltage can be applied. This enables optimization of the RILIS-mode ion extraction independently of the electron density. Experiments have been performed using a prototype VADLIS with an adjustable extractor plate voltage for the generation of gallium ion beams at the off-line separator as well as magnesium, molybdenum and mercury ion beams at ISOLDE. A factor >2 increase of the VADLIS efficiency in RILIS-mode has been achieved.
Highlights
The Versatile Arc Discharge and Laser Ion Source [1] (VADLIS) combines the FEBIAD (Forced Electron Beam Induced Arc Discharge) ion source [2] and the RILIS (Resonance Ionization Laser Ion Source) [3], both employed at Isotope Separator On Line (ISOL) facilities for the production of radioactive ion beams
The ISOLDE variant of the FEBIAD is known as the VADIS (Versatile Arc Discharge Ion Source) [4] but they share the same design and operating principle based on electron impact ionization
In this study we focus on the electric field distribution caused by the electrons reaching the anode cavity, combined with the voltages applied to the ion source walls and external electrostatic fields reaching the extraction zone
Summary
The Versatile Arc Discharge and Laser Ion Source [1] (VADLIS) combines the FEBIAD (Forced Electron Beam Induced Arc Discharge) ion source [2] and the RILIS (Resonance Ionization Laser Ion Source) [3], both employed at Isotope Separator On Line (ISOL) facilities for the production of radioactive ion beams. It was demonstrated that the VADIS cavity could be used as an effective laser-atom interaction region provided that the lasers can be transmitted through the 1.5 mm diameter exit aperture of the anode [1] In this case the ion source is operated in so-called RILIS-mode, with the source magnet and the anode voltage optimized for laser-ion survival and extraction, whilst keeping the anode voltage below the required value for electron impact ionization to occur. The development of this multi-purpose ion source (known as the VADLIS) has been crucial to the success of several experiments at ISOLDE since its first on-line use in 2015. In the outlook we discuss the prospects of this modified VADLIS as the new standard configuration, and suggest further modifications for improved ion source flexibility, diagnostics and performance
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