CERN Accelerating science

 Successful tests of canted correctors for HL-LHC
 by Panos Charitos (CERN)

The High-Luminosity upgrade of the LHC (HL-LHC) will extend the discovery potential of the world’s largest accelerator. The upgrade aims to increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten.

To reach these goals, a wide range of magnets and new technologies are currently under development. There will be about 100 magnets of 11 new types: four types of main magnets and seven different types of correcting magnets. In addition to the dipole and quadrupole magnets that guide and focus the charged particles, corrector magnets are used to cure imperfections in the magnets and compensate for alignment errors.

Among them, 2-m-long orbit correctors with an ultimate field close to 3 T will be positioned near the insertion region of the ATLAS and CMS experiments. These magnets will be used not only to correct imperfections and alignment, but also to open the crossing angle (between the two beams) avoiding parasitic collisions in the detectors. The team working under the HL-LHC project selected for this intermediate field a “canted cos theta” design with Nb-Ti superconducting wire. This type of winding configuration superposes two concentric and oppositely tilted solenoids (see Fig.1), to produce a pure dipole field. “This design has been proposed long time ago, but this will the first time to be used in a high energy physics particle accelerator” – says G. De Rijk, in charge of the magnet laboratory building the corrector.

Figure 1: Drawing showing the magnetic field lines around the corrector magnets designed for HL-LHC.
(Image credit: HL-LHC collaboration)

A 0.5-m-long short model was an essential step to demonstrate the validity of the design and of the technological solutions. It was tested in August 2017 at CERN and successfully reached the ultimate field. The 2-m-long prototype is expected to be tested by the middle of 2018. Even though this design requires about 50% more conductor than usual sector coils, this should be widely compensated by the simplicity of construction. “This magnet has 10 drawings instead of 100, so less components and less tooling to assemble – at the end, a less expensive and a more reliable magnet” explains G. Kirby, in charge of the magnet development.

A 0.5-m-long short model was tested in August at CERN. It was an essential step to demonstrate the validity of the design and of the technological solutions. (Image: Glyn Kirby/CERN)

It is the first time that this design is studied at CERN while Berkley magnet lab and PSI are exploring the applicability of this concept for higher-field magnets based on Nb3Sn. This novel approach has also great potential for intermediate fields required for medical applications - Berkeley National Labs are developing a gantry for cancer therapy.