The LHCb magnet is taking shape

The upper coil of the LHCb magnet was installed in the underground experimental hall at Point 8, giving this first element of the detector its final form.

The LHCb magnet holds no secrets for its creators: Wilfried Flegel, Jean Renaud, Marcello Losasso, Olivier Jamet and Pierre-Ange Giudici. Recently, they have even started to regard it as their own pet monster, with its mouth wide open, ready to spit out the particle flux that will pass through it from 2007 onwards. The magnet acquired this final look last month: two identical coils, measuring 7.5 metres long, 4.6 metres wide and 2.5 metres high, facing each other like a gigantic set of jaws. In March, the upper coil was mounted above its lower partner, giving the magnet its mouth-like appearance.


The "creature" seen with its creators! From left to right, the leading members of the LHCb magnet project: Pierre-Ange Giudici, who organised and supervised the industrial production of the coils, Marcello Losasso, who performed the 3D calculations to optimise the magnetic field, Olivier Jamet, responsible for the 3D design, Jean Renaud, in charge of the magnet assembly, and Wilfried Flegel, project leader.

This distinctive shape is the result of a compromise between the requirements of LHCb, which will study CP violation, and the choice to use a classic magnet to enable the experiment to stay within budget and on schedule (see Bulletin 05/2003). "The magnet was designed to provide a vertical magnetic field with a bending power of 4 Tm for charged particles with a 10 m track length. Its special feature is a large, conical aperture (the distance between the vertical pole pieces varies between 2.2 m at the entrance side and 3.5 metres at the exit side), which produces a non-uniform field in beam direction and a relatively high stray field outside the magnet. To improve the field uniformity horizontally across the aperture, the sides of each coil had to be bent. In addition, large iron pieces, known as "shims", were added to the sides of each pole piece," explains Wilfried Flegel, who developed the magnet and leads the project.
The upper coil, weighing around thirty tonnes, is currently on a support that will hold it temporarily in place until the complete upper part of the magnet yoke has been mounted. This upper yoke part, which is symmetrical to the lower one, will comprise 27 steel sheets, each measuring 11 metres long and weighing about 25 tonnes. Once the upper part has been completed, at the beginning of May, the upper coil will be fixed to it. All the aluminium "pancake" layers of conductor for each coil will then be connected up and their cooling system installed. The temperature of the magnet - which is warm, rather than superconducting - must not exceed 50° C.
This summer, the magnet will be moved sideways in the underground hall by about 20 metres to take up its final position. Then, during autumn 2004, its magnetic field will be mapped. At the same time, the calorimetry system, another key component of the LHCb detector, will start to be assembled.


In December 2003, the lower coil of the LHCb magnet was turned over ready for installation. This was a delicate operation, which was prepared and carried out by the team of crane operators working on the LHCb site.