CERN Accelerating science

The Transition Radiation Detector (TRD)  performs electron identification and triggering on electrons and jets, providing a trigger decision in about 7 microseconds.

TRD is composed of 522 detectors, arranged in 18 sectors in azimuth, each of 5 stacks in longitudinal direction, with 6 layers per stack. The diameter of the TRD cylinder is about 7 m and the length 7 m. It has 1.15 million channels of readout, each sampling the signal in 20 time bins. The active gas is a xenon-CO₂ mixture.

Details of the working principle of TRD is in the link here.