Uppsala University in Sweden has been a valuable collaborator since the foundation of CERN. In the 1950’s, Uppsala, having just constructed its own cyclotron, contributed to the development of the very first accelerator at CERN: the synchrocyclotron. In the 1980’s CERN assisted Uppsala with the construction of a proton and heavy-ion accelerator and cooler-storage ring named CELSIUS. Now Uppsala University is upgrading its superconducting cavity test facility, initially constructed for the ESS project, to test superconducting magnets and crab cavities for the HL-LHC.
In 2011, Uppsala University established the FREIA Laboratory for accelerator development. It has been equipped with a horizontal cryostat “Hnoss” and a cryomodule test stand for superconducting cavities. The design and construction of a vertical cryostat called “Gersemi” started in 2016. A very unique feature of Gersemi is the double functionality for both cavity and magnet testing. Cavities are tested in 2K liquid helium at sub-atmospheric pressure, essentially by having a large capacity vacuum pump connected to the liquid helium bath. Magnets on the other hand are tested in a 2K bath at atmospheric pressure. Magnets also create a magnetic field that can magnetize any metallic parts around the cryostat (i.e. reinforced concrete) while cavities are very sensitive to magnetic fields in general. This puts substantially different requirements on the functionality of the cryostat. Gersemi uses different “inserts” for cavity and magnet testing and has a set of external compensation coils to shield cavities from magnetic fields.
Gersemi has been installed and commissioned with the cavity insert at temperatures down to 4K and 2K in December last year. Preparations for testing a HL-LHC crab cavity prototype are ongoing. Regarding the magnet testing, on 23rd June, Kevin Pepitone, magnet test engineer, reported:
Today was a great day, for the first time a superconducting magnet was powered at FREIA. I tested the isolation (1kV 1min and 5min) and then the continuity of the cabling by measuring the voltage taps all along the current leads and superconducting cables (18V, 45mA). The cryostat and the insert were at warm temperature, but the results are promising for the tests at cold.
The successful commissioning of the new equipment at Uppsala establishes the FREIA laboratory as an important complement to the SM18 test facility at CERN, in time for the testing of new HL-LHC components.