Performance optimisation of the micro pixel chamber

A thorough performance analysis of large-area μ -PIC detectors has been made. Through systematic simulations and comparison with test results of the two detector versions, μ -PIC1 and μ -PIC3, we have identified that low primary electron collection was responsible for the degradation of measured gas gain of the μ -PIC3 device. The test of a new detector, μ -PIC5, fabricated with a narrower inter-cathode gap and anodes raised above the insulator surface, shows a threefold increase in gas gain reaching 104 in argon 80%–ethane 20% gas mixture, which agrees with simulations. The new detector demonstrates a stable long-term operation at high gains, above 6000 measured during more than 70 h with an X-ray source, with a moderate 6% gain increase due to dielectric polarisation.