In the following picture you can see the different parts of the ALEPH detector which was one of the four detector systems built for the LEP accelerator (Large Electron-Proton). In this 27 km long ring electrons and positrons were accelerated in opposite directions to a velocity close to the velocity of light before colliding right in the center of the detector systems. If the energy is high enough when the electron and positron annihilate, new particles are produced which are measured in the detector. The particles may have different properties like charge, mass and therefore you need different detectors (or chambers) to detect them. To distinguish particles of using their charges you need a magnetic field which is produced by a superconducting magnet coil. The coil is arranged so that the homogenous magnetic field is parallel to the beam axis.