FTPC Readout Chambers

The readout chambers are the first to combine fully radial readout with gas amplification by wires. The trick employed is to keep the wires at a small angle to the pads, so that each pad is crossed by an equal length of at least three sense wires.

As soon as the angle alpha exceeds 9 degrees (2 wires cross each pad), the structure in the position resolution that is introduced by having sense wires parallel to the pads disappears. The plots show the position of a laser beam measured by the chamber versus the real laser position.

The padplane consists of a sandwich of layers of Bendflex, a flexible electronics layout material. The sandwich provides gas tightness while at the same time allowing for electric connections from the pads to back side of the padplane. From there, kapton cables make the connection to the front end electronics.

The chambers are built by first glueing the wires to the flat padplane. This is done with conductive glue to avoid the need for later soldering and to limit the amount of non-conductive surfaces, which are vulnerable to electrostatic charge.
After the wires are connected, the padplanes are bent to the correct shape and inserted into the chamber frames, which have been machined out of solid blocks of aluminum for maximum stability and precision.