Precious pipes for the LHC

Special vacuum chambers have been developed for installation in the centre of the LHC experiments. Made of beryllium, the chambers are effectively transparent to the particles.

The first two beryllium chambers for the LHC experimental vacuum system have been delivered to CERN. The LHC will include a total of six beryllium chambers, covering 25 metres of the LHC ring. This is only a tiny fraction of the 50 kilometres of beam vacuum chambers in the LHC, but their number belies their significance. These are the chambers where the LHC beams pass through the very hearts of the experiments.

In ALICE, ATLAS and CMS/TOTEM, the beams will actually collide inside these cylindrical chambers, and all the resulting particles seen by the experimental detectors must first pass through the chamber wall. It is therefore critical that these chambers are as transparent as possible to these particles.

Beryllium metal is the material of choice for these chambers, as it is 20 times more transparent to particles than steel whilst being 50% stiffer and having only 25% of the density. However, it's also very difficult to work with, and must be handled with care. New technologies have been developed by industry in Russia and the US to respond to the strict vacuum requirements for the LHC, and the unprecedented size of the experiments. This has included machining and welding of beryllium with a scale and precision that was previously not thought possible.

For the LHCb experiment three conical beryllium chambers will be installed, totalling 12 metres in length, the largest with a diameter of 260 millimetres. This represents ground-breaking construction in this material. This has given the experiment a 5-fold reduction in the particle ‘background noise' compared with the equivalent aluminium vacuum chamber.

The chambers were designed in a close collaboration between the experimental collaborations and engineers in the AT vacuum group and TS design office. Over the course of the next few months the chambers will be prepared for installation in the four experimental caverns. This will include the addition of a thin film ‘getter' vacuum pump on the inside surface. Recently developed at CERN, this new technology gives a great improvement in the vacuum in the chamber, whilst allowing large vacuum pumps to be removed from inside the sensitive detectors.