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From antimatter to heavy isotopes, data-taking in physics facilities is resuming at CERN

With the Proton Synchrotron and its Booster accelerating protons to high energies again, the physics season can start at the ISOLDE radioactive ion beam facility and the Antimatter Factory


The ISOLDE beamlines seen from above
The ISOLDE's facility many transfer lines transport radioactive isotopes to experimental stations where their characteristics are examined (Image: CERN)

As the two-year-long shutdown of CERN’s accelerators comes to an end, some of the Laboratory’s many experiments are not waiting for the Large Hadron Collider (LHC) to wake up before starting to take data. The Proton Synchrotron (PS), CERN’s 60-year-old particle accelerator, and its injector, the Proton Synchrotron Booster, are back in full roar after a major overhaul. The Booster has begun delivering protons accelerated to 1.4 GeV to the ISOLDE facility (Isotope mass Separator On-Line Detector) and 2 GeV protons to the Proton Synchrotron, which, in turn, feeds its 26 GeV proton beam to the Antiproton Decelerator (AD, the first of the two particle decelerators of the Antimatter Factory). For the many experiments housed in these two world-class facilities, this can only mean one thing – the physics season is about to start, bringing with it the promise of exciting new results in nuclear and antimatter research.

“After optimising the experiment when the first proton beam reached the ISOLDE facility’s target on 21 June, physics data-taking started swiftly and the first experiment finished successfully after five days,” explains Gerda Neyens, Physics Group Leader at the ISOLDE facility. At ISOLDE, collisions between the Booster proton beam and heavy targets produce rare radioactive isotopes of elements from across the periodic table, of which specific ones are selected using a combination of lasers and electric and magnetic fields. This season’s first ISOLDE results came from the CRIS experiment in the form of hyperfine spectra of a series of silver isotopes synthesised within the walls of the facility. The atomic spectra of more than 20 exotic short-lived silver isotopes will reveal how the internal quantum structure, size and shape of the stable 107Ag and 109Ag isotopes change when neutrons are added to or removed from them.

For the upcoming physics season, ISOLDE will rely on new target stations to produce the radioisotopes, as well as an upgraded charge breeder (a device that removes electrons from the heavy isotopes) and a refurbished superconducting linear accelerator to accelerate the produced radioisotopes. The nuclear reactions occurring in the facility, which mimic and help understand those taking place inside stars, can thus be studied with greater precision.

Situated a few dozen metres away from ISOLDE, the Antimatter Factory uses the Proton Synchrotron beams to create its own peculiar substance. This process resumed on 28 June with the return of the beam on the new target: antimatter is being made at CERN again as you read. In this unique factory, antiprotons are synthesised by colliding the proton beams onto a target. The stray particles are then focused back into a beam thanks to a device called a “magnetic horn”, which was completely renovated in recent years, as was the target itself. The new target is an air-cooled piece of iridium placed in a graphite matrix and enclosed in a titanium alloy double shell. It will improve antiproton production, for a reliable and stable antimatter inflow over time.

The data-taking period that now awaits antimatter physicists has been given a boost by new machines such as ELENA (Extra Low Energy Antiproton deceleration ring), a ring that efficiently decelerates the antiprotons to unprecedented levels before feeding them into the experimental area. There, long-standing collaborations like AEGIS, ASACUSA and ALPHA stand next to fresh faces like ALPHA-G and GBAR, an experiment aiming to measure the freefall acceleration of antimatter under gravity. They will soon be joined by the PUMA and BASE-STEP collaborations, which were recently approved by the CERN Research Board. Both of these experiments will rely on the delicate process of transporting antimatter to neighbouring areas of the CERN site to study its properties.

Diversity is a defining characteristic of CERN, and this applies to the Organization’s research programme too. So, although the LHC and its detectors will not start buzzing and whirring for a few more months, there is no shortage of interesting developments: with antimatter and nuclear isotope data-taking and the forthcoming start of the physics season in the East and North experimental areas as well as at n_TOF, the next few months will be hectic ones for physics research.

A 360° virtual tour through the AD target area at CERN - use the arrows to change your perspective