Development of a very large area microstrip gas chamber for the CMS central tracking system

A very large area microstrip gas chamber (250 × 100 mm2), thought to be the building block of the CMS barrel tracker, has been built and undergone extensive tests with X-ray sources and particle beams. Rate capability, uniformity of response along the strip and charging-up effect for different gas gain and bias schemes have been measured in laboratory. A systematic study on the long-term stability of its performance (ageing) at high rates has been carried out both with standard and “clean” mechanical assemblies. Stability measurements under high voltage were performed. Studies of spatial resolution and efficiency for minimum ionizing particles were carried out with different gas gap, gas mixture, angle of incidence and avalanche gain.