XFEL: Cryostat from Poland for cryogenic tests

The complex inner workings of the 5 tonne, 4.5 metre high metal cylinder, which a Polish truck delivered to the AMTF hall on the DESY site after a ten-hour drive, is known only to specialists. The cryostat will be used to test the superconducting niobium cavities for the accelerator of the European XFEL. For this purpose, it will be working at temperatures two degrees above absolute zero (that is, at minus 271 degrees Celsius), and must be cooled and reheated on a weekly basis—an elaborate procedure that is only possible thanks to the sophisticated high-tech internal components.

The three main components of the Polish cryostats are a pressurized internal tank for superfluid helium in which four cavities will be suspended; a copper thermal shield that surrounds the helium tank and limits the influx of heat; and an external tank that encapsulates the internal high-tech components and maintains the vacuum. In addition, the cryostats include an array of high-precision instruments, such as special thermometers for measuring extremely low temperatures, helium pipes, heat exchangers, insulators, and special cryogenic elements. “The production of the cryostats gives us an opportunity to gain invaluable experience in developing large research facility elements, to access unique know-how, and to train our people,” Professor Grzegorz Wrochna, director general of the National Centre for Nuclear Research (NCBJ), declares in the press release of his institution. NCBJ is coordinating the Polish contributions to the European XFEL.

A day after its arrival, the first cryostat was propped up in the hall of the Accelerator Module Test Facility (AMTF) to be lowered later into a hole prepared in the floor. In the coming weeks, a team of Polish project partners will install and commission the cryostat.

The series test will start in November. Four superconducting niobium cavities at a time will be suspended inside each cryostat and subjected to a rigorous quality test. About 800 cavities will be tested in all. After passing the tests, they will be installed in groups of eight in 12 m long modules. The linear accelerator of the European XFEL will comprise 100 such modules (see the feature article “International resonance”).