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As fundamental building blocks of matter, protons are part of all the things that surround us. At the Paul Scherrer Institute PSI, though, they step out of their usual role and are deployed to generate other particles, namely neutrons and muons, which are then used to study materials. But for that, the protons first have to be accelerated. An important role in this is played by a three-stage accelerator facility, in the middle of which stands the accelerator known as Injector 2.

Magnets are the unsung heroes in particle accelerators because they keep protons or electrons on track. But such magnets have very little in common with the small ones on the domestic fridge door. Quite a few of the magnets at PSI are heavier and bulkier than the fridge itself, yet despite this they are also masterpieces of precision and control.

The source of the proton beam at PSI is a retro-style Cockcroft-Walton linear accelerator. Since 1984 it has been the first acceleration stage for protons which are taken up to around 80 percent of the speed of light by two further ring accelerators. This has resulted in the generation of a significant proton beam over decades, and which has even held the world record as the highest performing beam since 1994 thanks to ongoing retrofitting.