ECAL, the electromagnetic calorimeter

The calorimeter is made out of a cylindrical part called the barrel and two end caps to close the barrel. Each of these is made out of 12 modules. You can see the structure in perspective. The end caps are red and the barrel blue, the two upper barrel modules have been made transparent. It can also be seen projected along the beam axis, or in a transverse view.

Structure of the calorimeter modules

The modules from barrel and end caps have the same internal structure. It is made of stacks alternating wire chambers and lead sheets. You can distinguish three different stacks: the inner one contains 10 planes, the second one 23 and the last one 12. In the first two stacks the thickness of the lead is 2mm when it is 4 in the last. How many radiation lengths does it make?

The stack rests on a thick back plate and side plates keep the planes in place. On the inner face the pad structure is drawn. It proceeds through the module to create towers pointing toward the interaction region.

Structure of the sensitive medium

The sensitive medium is a wire chamber made of a comb in extruded aluminium. The wires run between the teeth. The comb is closed by a cathod cut into small pads. The pads are interconnected to build a tower looking toward the interaction point. The tower is read in three parts, per stack, called tower storeys.

More precise drawings can be obtained from the postscript files: along the beam axis, transverse view, global perspective, internal structure.