LHC collars - 12 million high technology gems
Some 12 million steel collars will keep the LHC dipole magnet structures rigid. Their production has just begun.A huge job began last week: the high speed manufacturing of twelve million steel collars for the 1250 dipole magnets of the future Large Hadron Collider, LHC.
The challenge is not only a matter of quantity: these collars are very high technology components because of the important role they play in the way the collider works.
One of the main difficulties with the accelerator is that the magnetic field that keeps particles in orbit must have the same configuration and intensity in all the dipoles. But when the 8.33 tesla magnetic field is on -100.000 times the earth magnetic field - it produces a very strong force that can deform the 'soft' parts of the magnets, such as superconducting coils. The force loading one metre of dipole is almost comparable with the weight of a Boeing 747 - about 400 tonnes - so a huge deformation would occur without a mechanical component to keep the whole structure rigid.
Diego Perini, CERN responsible for collar design and manufacture,brandishes a pair of these precious collars.
This component is the collar situated around the superconducting coils to prevent undesirable movements of the conductors. The collars must have well defined geometry and physical properties to confine the coils, to avoid deformations, and to have consistent behaviour when exposed to extreme heat and magnetic fields.
The problem has been solved using a particular alloy, belonging to the class of austentitic steels (see BOX), that has all the properties required: good thermal contraction and magnetic permeability. The production of this steel is possible thanks to the Japanese collaboration in the LHC project. The steel is produced by the Nippon Steel Company, then it is rolled into coils and shipped to Italy. When steel arrive at the Malvestiti Company in Milan, they are cut into the right shape using a very precise technique. The precision required for the dimensions of the collars must be in the order of ±20 microns. The technique used is called fine blanking, giving high precision and negligible deformation during the cutting procedure.
It is a long and accurate process that leads to the construction of a single pair of collars. But the real challenge is to build six million pairs that must be identical. Only then will the magnets constitute a rigid structure, and the magnetic field intensity be the same in every part of the collider so that particles feel the same magnetic field intensity when they are accelerated. The MMS group of LHC division supervises the construction and installs these components.
In the first year 5-6% of the total number of collars will be built, starting with a production of 5000 collars per week. Then production is planned to increase, with the aim of building the total number of collars in five years. Given the large number of collars, it is foreseen to have a second fine blanking company, which will start production during this year. As soon as each set of collars comes off the production line they will be assembled with other parts of the dipoles.
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