Arrival of the first main magnet for the new large FAIR ring accelerator: Start of series delivery of 110 magnets
Big progress is being made in the production of the components of the new FAIR particle accelerator facility at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. At the heart of the future facility will be the 1.1-kilometer ring accelerator SIS100, which is very challenging from a technological point of view. An important step has now been taken in the accelerator’s creation. It consists of the delivery of the first series-production main magnet for the new heavy-ion ring accelerator. The manufacture of magnets weighting several tons requires high-precision mechanical processing and analysis methods.
Special electromagnets and a special vacuum chamber are used to generate the magnetic field that forces the beams along a circular path. Both of these components are being produced by German manufacturers. The dipole magnets are being made by the company Babcock Noell (BNG) in Würzburg, while the vacuum chamber is being produced at the company PINK in nearby Wertheim. During operation, the dipole magnets are cooled to a temperature of -270 degrees Celsius in order to make the associated magnet coil superconducting. Unlike conventional copper cables, superconductors enable electricity to flow through them without any resistance. This allows the magnets to be made very compact and limits the amount of electrical pulse power that is needed for the accelerator facility.
Moreover, the magnets that are cooled to near absolute zero will enable the integration of a similarly cold vacuum chamber through which accelerated ion beams will travel. To accelerate intense beams of heavy ions, the interior of the beam pipe needs to have vacuum conditions that are very close to those found in outer space. The vacuum chamber acts like a superpump on whose walls the gas particles that are not eliminated by conventional vacuum pumps freeze.
The magnets are technologically challenging not only with regard to their superconductivity, but also with respect to the level of mechanical precision that has to be achieved in the interior. To achieve optimal results, each of the two magnetic poles have to be positioned parallel to one another with a precision of ±50 micrometers.
BNG, which was awarded to contract for manufacturing the 110 dipole magnets that are required for the heavy-ion synchrotron SIS100, was able to demonstrate that it has the production technology needed to do the job with the first of series (FOS) magnet. This first dipole magnet, which has already been delivered to GSI in Darmstadt, was cooled to near absolute zero at the series test facility that was especially created for this purpose and then operated at the high electric currents that are needed in accelerator operation. In this test, about 17,000 amperes of current flowed through a superconducting wire approximately one-centimeter in diameter. By way of comparison, a household circuit breaker generally trips at 25 amperes. High precision is crucial here as well. At such high currents, imprecise manufacturing could cause the wire to lose its superconductivity. The FOS dipole magnet achieved all of the specified properties during testing at GSI. After the acceptance tests were completed, GSI approved the magnets’ series production. BNG has equipped a new assembly hall specifically for this purpose.
The first dipole magnet to be completed after series-production approval was recently delivered to GSI following a successful factory acceptance test (FAT). Superconducting dipole magnets will be regularly delivered to GSI from now on. A total of 110 magnets will be supplied by 2019. Each magnet undergoes four weeks of testing after it arrives at GSI. Magnets that successfully pass these tests will be stored until the new accelerator tunnel is completed. The magnets will be installed into the tunnel beginning in 2021. The assembled particle accelerator is scheduled to be cooled to its operating temperature of -270 degrees Celsius for the first time in 2023. Soon thereafter, it will generate the first beam for experiments at the FAIR research facility.