50 years GSI



The new accelerator facility FAIR is under construction at GSI. Learn more.


GSI is member of


Funded by




Slow and just the right strength: New six-pole magnets for the SIS100 accelerator ring

Photo: G. Otto/GSI Helmholtzzentrum für Schwerionenforschung

The new sextupole magnet



The centerpiece of the future FAIR accelerator facility will be the 1.1-kilometer-long SIS100 ring accelerator, which will especially stand out because of its intense high-energy ion beams. To use these accelerated beams for experiments, they first have to be extracted from the ring accelerator. Darmstadt has just received the first of a series of six-pole magnets that will play a crucial role in the slow extraction process at the SIS100.

Beams can be extracted either quickly or slowly. During fast extraction, a device known as a “kicker” propels the entire beam out of the ring within a millionth of a second so that it can be transferred to one of the downstream storage rings, for example. The slow extraction process, on the other hand, takes several seconds to extract the circulating ions and keeps the intensity as constant as possible during the process. This type of extraction is required for the R3B and CBM experiments at FAIR, for example.

The new resonance sextupole magnet was delivered by the Danish company Danfysik and will be followed by five more magnets of this type. Each magnet weighs around 1.6 tons, measures 70 centimeters in diameter by 80 centimeters in length, and has three north poles and three south poles. The six magnets will be installed into the accelerator ring’s six segments. They will enable the ion beam to be slowly and continuously extracted from the SIS100 by means of the process known as resonance extraction. Once the desired beam energy level has been reached, the particles circulating in the ring are stimulated to resonate in horizontal oscillations around their intended track. Among other things, this is achieved by non-linearly focusing the appropriately programmed six resonance sextupole magnets. “The oscillations grow in amplitude within just a few revolutions, enabling the electrostatic septum to extract the particles from the SIS100,” explains As Peter Spiller, a project area manager at GSI responsible, among other things, for the construction of the ring accelerator SIS100. In this way, the resonance sextupole magnets enable the particle beam to be peeled off, leading to the extraction of a seconds-long flow of particles for use in the experiments.

“The first resonance sextupole magnet has now finished testing at the magnetic field measurement station at GSI Helmholtzzentrum für Schwerionenforschung,” state work package directors Carsten Mühle and Peter Rottländer. As a result, the magnets can now be approved for series production. Peter Spiller hopes the remaining magnets will be delivered soon. “The resonance sextupole magnets are important components of the SIS100 ring and essential for conducting the FAIR research program,” he says.

The new sextupole magnet
The first resonance sextupole magnet is tested at the magnetic field measurement station.
Photo: G. Otto/GSI Helmholtzzentrum für Schwerionenforschung