April 22nd, 2013

Accelerator Technologies Laboratory

The Accelerator Technologies Laboratory is unusual among CERN facilities in that it is open to the general public. You don't need to arrange a tour—just show up during business hours, walk in, and stay out of areas marked forbidden to visitors. This is where the heavy metal of the LHC was developed and tested, and continues to qualify components and develop upgrades. If you don't have a knowledgeable guide or haven't read up in advance on the components of the LHC, many of these amazing machines may be a mystery to you, but even so it's inspiring to know that humans have invented and built them in the quest to understand nature at its most fundamental level.

This is a big facility; note the bicycles for getting around.

I believe this is a segment of Linac4, being developed to replace the current Linac 2, which performs the initial acceleration of protons bound for the LHC. When it goes into service, it will allow increasing the luminosity (collision rate) of the LHC.

This also appears be a component of Linac4.

Just sayin'.

A section of the LHC tube reveals its inner structure. Note how the magnet encloses the two beam pipes at the centre, assuring that protons travelling in opposite directions are uniformly deflected.

A face-on view of the tube shows the symmetrical magnet structure enclosing the beam pipes.

In addition to the main magnets, which steer the beam around the LHC ring, a variety of magnets, shown here, form the beams so they arrive precisely at the interaction points with maximum density.

High-temperature superconductor current feeds, chilled with liquid nitrogen, supply current to the ring. This is a cross-section of a 13,000 ampere feed. Are superconductors cool, or what?

This is an end view of an LHC ring segment. This is a fully functional spare which could be installed should a segment fail. In the centre are the two beam tubes. Cooling and electrical feeds occupy the periphery.

An oblique view shows the scale of this tube. There are a total of 1232 of these 15 metre dipole magnets in the LHC ring. along with 392 5–7 metre long quadrupole magnets which focus the beam.

This cut-away view shows the junction between two sections of LHC tube. These connections must accommodate the transition between room temperature and the 1.9°K operating temperature of the accelerator, and hence incorporate intricate expansion joints.

This model illustrates one of the notorious splices which led to the September 19th, 2008 quench incident, which vented six tonnes of liquid helium into the tunnel and damaged over 50 superconducting magnets. It was more than a year before the LHC was repaired and could resume operations. In engineering on this scale, and at such extremes of energy and temperature, attention to even the most mundane of details is essential.

The eight sectors of the LHC are separated by isolation valves like this one. They allow taking a sector offline, storing its liquid helium coolant in dewars outside the accelerator, and bringing the beam tube up to ambient temperature and atmospheric pressure for maintenance while maintaining the vacuum and cryogenic temperature of adjacent sectors. This valve is a wonder to watch operate—words fail to describe it.

These bays allow component testing of sections of the beam pipe and magnets. Each section in the accelerator was tested here before being installed in the tunnel.

by John Walker May 12th, 2013

This document is in the public domain.