First experience with the HERMES silicon detector

A silicon detector system (the Lambda Wheels) is being added to the HERMES experiment at DESY. The acceptance of the front region will be enlarged in order to increase the fraction of Λ0, Λc, and J/Ψ-particles which can be reconstructed. The detector is located inside the ring vacuum. Two disks cover the area between 4.5 and 16 cm from the beam. The detector consists of 12 identical modules. This report describes some details of the design, the cooling and the read-out of the detector. A prototype of a single module has been operated since the beginning of 2000. A signal-to-noise ratio of about 10 has been obtained for minimum-ionizing particles.