Building Bridges: Polish Contribution for Bypass in FAIR Accelerator Ring has arrived
Without extreme cold, nothing at all functions properly in the new SIS100 accelerator ring, the heart of the future FAIR system. Components for FAIR are currently being designed and built around the world. A crucial component for the cooling system in the 1,100-meter-long ring accelerator has now arrived in Darmstadt. It is the first part of several bypass lines that are arranged around the entire ring to ensure that the cryogenic agent (liquid helium) is transported to the right places. Approximately 30 components of this kind, each up to 12 meters long, guarantee that the required low temperatures (-268.6 °C) are maintained through the ring system.
The first bypass segment is a Polish contribution to FAIR. It was manufactured by the company Kriosystem of Wrocław, Poland, based on a design and preliminary developments of the Wrocław University of Science and Technology (Politechnika Wroclawska). The Jagiellonian University (Uniwersytet Jagielloński) in Kraków is also playing a major role as a contractual partner of FAIR.
As Peter Spiller, a project area manager at GSI responsible, among other things, for the construction of the ring accelerator SIS100, explains: “The bypass ensures that the cold temperature can be maintained throughout the whole system.” The challenge faced by the cryotechnology here is that the powerful magnets of SIS100 that guide the particles, keep them on their circular path, and focus them must be extremely cold. However, other accelerator components that are operated at room temperature are connected up right next to the magnets, such as high-frequency systems, injection systems, or extraction systems. For these warm components, the system therefore needs a bridging mechanism that can act as a sort of Thermos bottle and maintain the extremely cold temperatures in the ring system at these spots too—a bypass.
There are six segments in the accelerator ring that must be bridged with bypasses, says Thomas Eisel, the work package manager responsible for the local cryogenics. The bypasses transport both liquid helium as a cryogenic agent and an electrical current of several thousand amperes to the magnets. For the synchrotron SIS100 of FAIR, the superconducting magnets are needed not only to guide the beam but also to cool down the vacuum chambers in the magnets to close to absolute zero. The residual gases in the beam pipe then adhere to the extremely cold chamber surface, so that an extremely low residual gas pressure is generated in the beam pipe. The magnet chamber thus serves as a super vacuum pump. An extremely good vacuum is indispensable for generating heavy ion beams with high intensities, one of the core jobs of FAIR.
But superconductivity is only achieved when the magnet coils are cooled with liquid helium to the extremely low temperature of 4.5 Kelvin (-268.6 °C). That is the temperature norm for the whole cryomagnetic system of SIS100.
The approximately seven-meter-long segment of the bypass that has now been delivered is currently being kept in the test facility of GSI and FAIR, where it will be closely examined beginning now: It will be cooled down to -268.6° C and then tested to ensure it can withstand a number of different stress conditions. Is everything well insulated, or are there weld seams that aren’t sealed? Does any helium escape? Does the superconductivity break down? Is damage incurred because of the high electrical current? If all the tests are passed, the bypass segment will be placed in temporary storage. In the coming months, more components are expected to follow.