A large area optical imaging uv detector operating with TMAE at 48 dregee C

We describe the multistep avalanche chamber (MSAC) used in the experiment NA35 at CERN as photon detector of a ring imaging Cherenkov counter (RICH) that upgraded the experimental setup of a vertex streamer chamber by providing particle identification in the 1.5–3.5 GeV/c region. The chamber design contains some innovative technical solutions to limit the sparking rate and to allow the sensitive area to be larger than the present 50 × 50 cm2. The detector is read out optically using a CCD camera in conjunction with a system of light intensifiers, since the optical readout offers a convenient way to record events in a two-dimensional array. Construction details and test results are discussed.