The Construction And Performance Of A Large Cylindrical Wire Chamber With Cathode Readout

The construction and performance of two large coaxial cylindrical multiwire proportional chambers with cathode readout, denoted as Z-detector, forming the outer part of the L3 central tracking detector, are described. Three self-supporting cylinders of about 1 m length and 1 m diameter, constructed as a sandwich of Kapton foil and foam, form the mechanical frame. In each chamber one cathode layer is subdivided into helical strips and the other one in rings. The readout of the charges induced on the cathode strips provides the avalanche position along the beam (z) direction. The detector has been running in the L3 experiment at LEP for nearly two years. The resolution of the z-measurement is 320 mum, the double track resolution is 10 mm. The efficiency of each chamber is 96%.