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ISOLDE’s new Offline 2 source nears completion

The final touches are being put to the new test facility to ready it for operation


ISOLDE's Offline 2
Offline 2 in its enclosure at CERN’s Meyrin site (Image: Julien Ordan)

During the ongoing second long shutdown of CERN’s accelerator complex (LS2), ISOLDE is upgrading its target test facilities. The so-called Offline 1 will be supported by the brand new Offline 2 facility in the coming months.

ISOLDE, which stands for Isotope Separator On-Line Device, is CERN’s longest-running experiment facility, having been first switched on in 1967. It specialises in producing radioactive isotopes of elements, allowing scientists to study exotic nuclei that would rarely, if ever, occur naturally in the universe.

“It works by firing a 1.4-GeV proton beam from the Proton Synchrotron Booster into specially prepared targets,” explains Stuart Warren (EN/STI), who worked on ISOLDE for three years. “The elements in these targets undergo physico-chemical processes resulting in the production of specific radioactive isotopes.” Once produced, the neutral atoms are ionised so they can be accelerated by electric fields and transported for study. Powerful magnets bend the beam in transport, separating the different isotopes based on their masses, while electrostatic quadrupoles focus the particle beam for delivery into ISOLDE’s various experiment set-ups.

“To make new isotopes, we have to test different targets,” continues Warren, “but we cannot do this in the ‘online’ part of ISOLDE, as it is in high demand for research-data collection throughout the year.” In addition, the “online” facility is highly irradiated from the proton beams and the nuclear reactions, limiting the time that scientists can spend in its vicinity. ISOLDE has therefore had an “offline” facility that allows scientists to test not only new targets for their suitability, but also the parameters needed to extract the best quality of radioactive-isotope beams. The target in the offline part is heated by a 1000-A supply, which causes the atoms to evaporate and diffuse from the target, after which they are ionised and sent through the beam lines.

Recently, increasing demands on the original offline facility, now called “Offline 1”, led to the decision to build a second one to complement it. “I have spent the last three years designing and building ‘Offline 2’ with my colleagues Tim Giles, Carlos Muñoz Pequeño and Annie Ringvall-Moberg,” beams Warren.

Offline 2 is located next door to Offline 1 and is enclosed in a Faraday cage covering 40 square metres. It is designed to be as similar to the online facility as possible. For example, its radiofrequency quadrupole cooler and buncher (RFQcb) is a replica of the one used in ISOLDE proper. Warren and company have also put in place systems to conduct automatic tests of new targets and record data over large durations. With Offline 1, this needs to be done manually, resulting in a limited number of datasets being available.

Next week, Offline 2 will begin its six-month commissioning phase, which will include the installation of a dedicated laser bench and other tools. When proton beams return after LS2, Offline 2 will work in parallel with Offline 1 to cater to the needs of target and ion-source development in order to sustain ISOLDE’s comprehensive physics programme.

More photos of Offline 2 on CDS