Cryogenic testing of magnets: First quadrupole units for the large FAIR ring accelerator tested
Hundreds of powerful magnets will be needed to guide particles in a precise beam at nearly the speed of light at the future accelerator center FAIR, which is currently being built at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. Widely varied types of magnets and magnet systems are used for this purpose. They include the 168 quadrupole magnet units that will be used in the large SIS100 ring accelerator. These units are being manufactured and tested by Russia and represent an important non-cash contribution to the FAIR project. The two first of series (FoS) quadrupole units were manufactured in 2017, and at the end of the year they were successfully subjected to cryogenic tests at temperatures near absolute zero. The tests are another important step in the development and construction of the SIS100.
The quadrupole units, weighing tons, consist of a superconducting quadrupole magnet that is combined in a variety of arrangements with superconducting sextupole and steering magnets. Unlike conventional copper cables, superconductors enable electricity to flow through them without any resistance. In order to achieve superconductivity, the units are cooled down to ‑270 degrees Celsius during operation.
The acceptance tests for the FoS units were conducted in the presence of a team of experts from GSI and the responsible work package manager, Egbert Fischer. The quadrupole magnets worked flawlessly during the performance tests at an operating temperature of 4.5 K (i.e. 4.5 degrees Celsius above absolute zero, which is about -273 degrees Celsius). During fast-pulsed operation at 23,000 amperes per second, the magnets surpassed the intended maximum operating current of about 12,000 amperes. Initial evaluations of the measured magnetic fields indicate that the units are of a sufficiently high quality within the range of the defined requirements.
The FoS units will soon be accepted and sent to FAIR. Series production is scheduled to be approved in the near future. GSI will subject the two units to an initial integration test, in which they and other installations will be mounted onto a carrier system.
Over the past four years, GSI and the Joint Institute for Nuclear Research (JINR) have built a high-performance testing facility in Dubna, Russia, to conduct cryogenic testing of the units from the series. The facility was put into operation during an official ceremony in late 2016. It tests superconducting magnets for the two future accelerator centers FAIR (Facility for Antiproton and Ion Research) and NICA (Nuclotron-based Ion Collider fAcility), which are currently being built at GSI in Darmstadt and at JINR in Dubna, Russia, respectively. About half of the tests at the facility will be of magnets for the NICA project, while the other half will be of magnets for the future SIS100 accelerator at FAIR. A corresponding contract for the operational implementation of the serial tests will be signed soon. The contract will require JINR to conduct the site acceptance tests (SATs) of the quadrupole units on behalf of GSI.
For the construction of FAIR, researchers are developing and using ultra-innovative methods and techniques in numerous areas. One example of that is the main quadrupoles of the units that recently underwent cryogenic testing. The quadrupoles are based on a technology that was originally developed for the Nuclotron accelerator at JINR. The key element of this technology is a Nuclotron cable that consists of superconducting strands wrapped around a copper-nickel tube. This cable technology is completely different from that of Rutherford cables, which are employed in high-field magnets. The new technology is especially well suited for the construction of superconducting magnets that enable fast electric current changes (high ramp rates). In a development process lasting several years, GSI and JINR optimized the Nuclotron magnet technology for use in the FAIR ring accelerator SIS100.
The focus was on reducing dynamic losses (heat input) at high ramp rates, optimizing the magnetic design, and adapting the system to a new high-current Nuclotron cable that offers sufficiently low hydraulic resistance. The steering magnet technology is based on a further development of the nucleon cable that was created specifically for FAIR’s SIS100 ring accelerator. In this system, the strands are insulated from one another so that the number of turns of a coil can be significantly increased even though the current is reduced.
The development of this new kind of cable was initially supported by a program funded by the German Federal Ministry of Education and Research (BMBF) and JINR. The development process was successfully completed when the first two SIS100 units were accepted. (BP)