The wire chambers must be able to perform non-destructive read-out with several planes with a few milimeters pitch. They have to be built out of non-contaminating materials and must stand the thermal stress of going from room to LAr temperature. The precision and the reliability of the mechanics has to be high, and a good knowledge of the electric field in the detector must be granted.
Each TPC consists of a system of three vertical, parallel wire planes (17.95 x 3.16 m2 of common surface), 3 mm apart from each other. Two TPCs are installed in each T300, positioned on the opposite, vertical long sides of sustaining structure. The distance between the two TPCs is 3.00 m, with the cathode plane (parallel to the wire planes) placed in the middle. This sets at 1.5 m the drift length of the active volume for both left and right chambers.
Wire directions in the three planes run at 0o and +-60o with respect to the horizontal direction. The first plane (0o and the second plane -+60o in both right right and left chamber) facing the drift volume work in induction mode and are called Induction-1 plane and Induction-2 plane. The third plane (-60o in both right and left chamber) works in charge collection mode (Collection plane). The wire pitch is 3 mm for all planes.
The wires are anchored by special holders onto the wire frame in groups of 32 units (the wire modules). Each holder is formed either by one or two (according to the different cases) PEEK combs contained in stainless-steel supports which also embed one or two printed boards. The wire ferrules held by the PEEK shell terminating the wire module at each end are hung on the comb pins. A circuit printed on the board establishes the electric connection between the 32 pins of the comb and a single connector also mounted onto the board.
The wire modules are individually mounted onto the beams of the elastic frame (de-tensioned position). The elastic frame is schematically subdivided into portions (about 2 m long). Each portion comprises 18x2 combs/connectors. Once the installation of the TPC wire modules is completed, wire tension is restored by loading the springs of the movable wire frame.
During detector operation, the read out of the ionization tracks from the various planes (non-destructive read-out) is accomplished by biasing the planes at suitable potentials.