Transition Radiation Tracker - TRT


The TRT consists of a barrel section, which covers the rapidity region from approximately -0.9  to + 0.9,  and two endcap regions which extend the rapidity coverage to approximately - 2.5 to +2.5.  The barrel region consists of 96 modules with 1.5 m straws parallel to the beam axis. The EndCap detectors each contain 18 wheels with radial straws, each approximately 40 cm in length.

Barrel Modules of TRT



Diagram of the barrel section of the TRT which is comprised of 96 individual modules, 32 each of three different sizes. Each module at the smallest radius contains 329 straws, the modules at intermediate radius, 520 straws, and the modules at the outermost radius, 793 straws. The wires in the straws are electrically split in the middle so that each end of the straw is read out separately.

Photograph of one of the barrel modules.

Exploded view of the end of one of the barrel modules showing, from right to left, the carbon fiber shell, radiator, individual straws, HV plate, and tension plate on which the wires are terminated. The electronics is mounted directly on the tension plate.

End Cap Wheels of TRT

There are three types of wheels - A, B, and C going from closest to the barrel to the highest eta region. The photo below shows the first layer of straws for a prototype A wheel being assembled at CERN. A full A wheel has over 9,000 straws, but the full 16 layer assembly is made up of sub-assemblies of four layers each.


The anode is brought out on the outer rim of the wheel through a rigid-flex multilayer circuit board called "the Web" which makes connection to the straw (cathode) and the wire (anode) via two separate kapton layers using a novel attachment technique called petals. The HV (cathode) petals are just visible in this photograph as gold plated circles with starred cut outs. The triangular petals are forced into and against the straw wall via a plastic plug to make the cathode connection. A fixing pin serves the same function for the wire.


The drawing below shows the web HV connections (red) and signal connections (blue).

           Last Modified  - 31 January, 2001 - RVB