The construction of a micro-pattern gas detector of dimensions
40 x 10 cm² is described. Two gas electron multiplier foils
(GEM) provide the internal amplification stages. A two-layer
readout structure was used, manufactured in the same technology
as the GEM foils. The strips of each layer cross at an effective
crossing angle of 6.7 degrees and have a 406 micro-m pitch. The
performance of the detector has been evaluated in a muon beam at
CERN using a silicon telescope as reference system. The position
resolutions of two orthogonal coordinates are measured to be
50 micro-m and 1 mm, respectively. The muon detection efficiency
for two-dimensional space points reaches 96%.
Key words:
detector, position sensitive, GEM, two-layer readou
