Special superconducting quadrupole magnets for squeezing the beams at CERN’s LHC collider have been successfully developed at the Japanese KEK laboratory as part of the LHC co-operation programme between CERN and KEK.
Since 1997, two model magnets have been made. The first reached the maximum operational field gradient of 220 T/m at the third training quench and has successfully achieved the maximum field gradient of 250 T/m at 1.9 K after thermal cycling and training. The second model reached 222 T/m at the first quench.
KEK has undertaken to provide magnets for the inner triplets, which provide the final focusing of the LHC beams for the four planned major experiments: ATLAS, CMS, LHC-B and ALICE.
KEK and Fermilab will each provide 16 of the 32 magnet cold masses, and Fermilab will be further responsible for the integration of the magnets within the cryostats.
The magnet features a high design field gradient of 240 T/m and a large coil aperture of 70 mm, and it must provide long-term stable operation at 200220 T/m under the heat owing to lost particles and showers from the colliding beams.
The magnet consists of four-layer coils wound with NbTi/Cu compacted strand cables closely surrounded by an iron yoke to maximize the magnetic field, and also to function as the mechanical structure that supports the electromagnetic force.
The field quality of the model magnets has also been evaluated and the measurements indicated a necessary adjustment of the two-dimensional design of the coil to reduce the 20-pole component, according to the recent study of the beam dynamics carried out by the US team.
A third 1 m model is being developed to finalize the design. The full-scale prototype magnet programme will begin this year and extend to full production by 2001.
