Rutherford Cable and their constituent composite filamentary superconductors were used for both high field solenoid magnets and accelerator magnets. High field solenoid magnets generate fixed magnetic fields, enabling the analysis of particle collision and identification of collision products.
Recognizing their long-standing expertise in superconductivity, RAL was tasked with the design and manufacture of solenoid magnets for DELPHI and H1. We focus on the latter as DELPHI’s construction, and its eventful journey was covered here. This superconducting solenoid was for the H1 experiment, a detector within the HERA accelerator complex at DESY in Germany.
Beginning in 1986, RAL would begin winding of NbTi into 22km of aluminum stabilised Rutherford Cable. Using modified manufacturing apparatus for DELPHI, H1 solenoid coils were made through a novel technique developed at RAL called internal winding. The 22km of coils were lowered into a colossal cryostat vessel, RAL had designed the cryogenic interfaces ensuring intimate contact to the coils. A major aspect of this contribution was the cryogenic control system, which included the cryogenic valve box. This would control circulation of refrigerants, being able to route liquid helium throughout the coils with high precision.
H1 Coils being assembled at RAL (1986)
Innovations in Rutherford Cable production and cryogenic engineering for DELPHI and H1 magnets would provide experience within the manufacture of solenoid magnets for CERN’s upcoming LHC project.
After a decade of construction, the world's most powerful accelerator complex, the LHC was completed in 2008. CERN would continue their ongoing search for the elusive Higgs boson, with general-purpose detectors ATLAS and CMS poised to make its discovery. A strong magnetic system was integral in maximizing the experimental sensitivity.
RAL was part of a UK collaboration to deliver components of the ATLAS magnetic system, with the main contribution being the two fundamental End Cap Toroid magnets. The End Cap Toroids were designed by a team from Applied Science Division at RAL in collaboration with members of Particle Physics Department and UK Universities. The RAL team then oversaw the manufacture of its components. Standing at an impressive 10-meter diameter that fit snugly inside the central Barrel Toroid to optimise the performance of the ATLAS detector. Consisting of over 30km of superconducting coils, RAL would leverage its extensive experience in superconducting technology to ensure these were protected during quenching via high purity aluminum cladding of the Rutherford Cable.
End Cap toroid being transported for assembly (2007)
Elwyn Baynham, the project leader for the ATLAS end cap toroid describes various aspects of this design, ‘The two magnets possess a stored energy of 400MJ, an energy equivalent to the kinetic energy of a freight train travelling at 100kph. Should a quench occur then the superconducting coils would regain their resistance and current flowing through them would generate heat. High thermal and electrical conductivity of the aluminium would mitigate this energy dissipation by allowing current to flow into the aluminium. In the instance of localised heating, heaters within the magnet would be fired to distribute the energy evenly throughout the entirety of the coils ensuring that a temperature of 100K was not exceeded. Furthermore, a uniform distribution of circulating cryogenic coolant would maintain a controlled temperature profile of approximately 5K during normal operation’
ATLAS End Cap Toroid during assembly
Cooling these colossal coils to their operating temperature could take over a month and so the central cold mass of the end cap had to remain cryogenic. To ensure the magnet system could be moved out of the ATLAS detector during maintenance while remaining cold, the UK provided a set of dynamic lines positioned atop the toroid towers. These are likened to a ‘bicycle chain on a much larger scale’ it’d be stiff vertically though capable of spanning over 10m horizontally in a flexible manner.
Schematic of the ATLAS End Cap Toroid Dynamic lines
