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DELPHI was one of the four experiments installed at the LEP particle accelerator from 1989 - 2000. The silicon tracking detector was nearest to the collision point in the centre of the detector. It was used to pinpoint the collision and catch short-lived particles.

OPAL was one of the four experiments installed at the LEP particle accelerator from 1989 - 2000. OPAL's central tracking system consists of (in order of increasing radius) a silicon microvertex detector, a vertex detector, a jet chamber, and z-chambers. All the tracking detectors work by observing the ionization of atoms by charged particles passing by: when the atoms are ionized, electrons are knocked out of their atomic orbitals, and are then able to move freely in the detector. These ionization electrons are detected in the different parts of the tracking system. (This piece includes the vertex, jet and Z chambers) In the picture above, the central detector is the piece being removed to the right.

An accelerating cavity from LEP. This could be cut open to show the layer of niobium on the inside. Operating at 4.2 degrees above absolute zero, the niobium is superconducting and carries an accelerating field of 6 million volts per metre with negligible losses. Each cavity has a surface of 6 m2. The niobium layer is only 1.2 microns thick, ten times thinner than a hair. Such a large area had never been coated to such a high accuracy. A speck of dust could ruin the performance of the whole cavity so the work had to be done in an extremely clean environment. These challenging requirements pushed European industry to new achievements. 256 of these cavities were used in an upgrade of the LEP accelerator to double the energy of the particle beams.

The pulse of a particle accelerator. 128 of these radio frequency cavities were positioned around CERN's 27-kilometre LEP ring to accelerate electrons and positrons. The acceleration was produced by microwave electric oscillations at 352 MHz. The electrons and positrons were grouped into bunches, like beads on a string, and the copper sphere at the top stored the microwave energy between the passage of individual bunches. This made for valuable energy savings as it reduced the heat generated in the cavity.

Model of the tracking detector for the CMS experiment at the LHC. This object is a mock-up of an early design of the CMS Tracker mechanics. It is a segment of a “Wheel” to support Micro-Strip Gas Chamber (MSGC) detector modules on the outer layers and silicon-strip detector modules in the innermost layers. The particularity of that design is that modules are organised in spirals, along which power and optical cables and cooling pipes were planned to be routed. Some of such spirals are illustrated in the mock-up by the colors of the modules. With the detector development it became, however, evident that the silicon detectors would need to be operated in LHC experiments in cold temperatures, while the MSGC could stay in normal room-temperature. That split in two temperatures lead to separating those two detector types by a thermal barrier and therefore jeopardizing the idea of using common, vertical Wheels with services arranged along spirals.

This is a slice of a LEP dipole bending magnet, made as a concrete and iron sandwich. The bending field needed in LEP is small (about 1000 Gauss), equivalent to two of the magnets people stick on fridge doors. Because it is very difficult to keep a low field steady, a high field was used in iron plates embedded in concrete. A CERN breakthrough in magnet design, LEP dipoles can be tuned easily and are cheaper than conventional magnets.

Chorus light guide and a selection of fibres in wooden box.

Muon detectors from the outer layer of the ATLAS experiment at the Large Hadron Collider. Over a million individual detectors combine to make up the outer layer of ATLAS. All of this is exclusively to track the muons, the only detectable particles to make it out so far from the collision point. How the muon’s path curves in the magnetic field depends on how fast it is travelling. A fast muon curves only a very little, a slower one curves a lot. Together with the calorimeters, the muon detectors play an essential role in deciding which collisions to store and which to ignore. Certain signals from muons are a sure sign of exciting discoveries. To make sure the data from these collisions is not lost, some of the muon detectors react very quickly and trigger the electronics to record. The other detectors take a little longer, but are much more precise. Their job is to measure exactly where the muons have passed, calculating the curvature of their tracks in the magnetic field to the nearest five hundredths of a millimetre. Even these precision detectors are not exactly sluggish – they react within a millionth of a second. Such a fast response is essential when new collisions are occurring in the centre of ATLAS 40 million times every second! This muon detector is a drift tube - an aluminium tube with a wall thickness of some 1/10 mm that is filled with a special gas mixture. Inside the tube there is a wire that is tightened all over the length of the tube and fixed at the end caps. Particles (or ionizing radiation) that enter the tube ionize the gas molecules and liberate electrons. Since there is a high voltage between the wire and the tube wall, the released negatively charged electrons move towards the wire in the centre of the tube. On their way to the central wire, the moving electrons induce an electric signal that can be amplified and registered by further electronics.