Status of the SPES Laser Ion Source

by Omorjit Singh Khwairakpam (INFN - LNL)

Wednesday 14 May 2025, 14:30 → 16:30 Europe/Rome

C. Villi meeting room

 

 The SPES (Selective Production of Exotic Species), located in INFN-LNL, Italy, is an ISOL (Isotope Separator On-Line) facility dedicated to the production of radioactive ion beams (RIBs). SPES employs three different types of ion sources namely surface, plasma and resonant ionization laser ion sources (RILIS).

The RILIS method employs stepwise photo-ionization schemes that are element-specific, distinguishing it from other ionization techniques by offering superior elemental selectivity. When combined with mass separation, RILIS enables the production of high-purity isotopic beams with minimal isobaric contamination.

The geometry of the SPES-Laser Ion Source (SPES-LIS) has been realized as a result of the thermal optimization of the ISOLDE MK1 ion source. The SPES-LIS is made of tantalum, and is composed of a hot cavity, a transfer line, and an alignment system. Its full characterization was performed in ISOLDE Offline 2, CERN in two independent experimental campaigns back in 2023.

Laser enhancement ratio of the ion yield and time structure of the ion beam has been measured in relation to the production of samarium and gallium ions. The time structure of the laser ion beam from the SPES-LIS reveals that a large number of ions, roughly 50% of the total, are produced from the transfer line which was not observed for the ISOLDE MK1 source. This effect is attributed to the actively heated transfer line system in the SPES-LIS which provides an ion guide along the whole length of the ion source.

The experimental measurements were performed under various ion source temperatures and ion load conditions, primarily influenced by surface ion contaminants. Through this comparative study, it was also observed that the radial ion confinement in the transfer line could be further optimized for high ion load conditions, which is particularly critical for the production of medical radionuclides with inherently low in-target yields.

Furthermore, laser resonance ionization efficiency measurements for the production of gallium were performed, with a reported value of 27.2%. This measurement sets a crucial reference as it was the first completed set of laser ionization efficiency performed in the facility of ISOLDE Offline 2.

A key point of the seminar is to provide an update on the existing SPES laser ion source and to highlight the advantages of such technique in an ISOL facility which aims to provide high purity isotopic beam. Discussion on the possible optimization of the laser ion source will be presented.