Study of efficiency and gain uniformity at different gas flow rates of a quad-GEM detector

A quad-GEM is particularly useful for its low ion back flow, excellent rate capability, good position resolution, high gain at relatively low operating voltage in the next generation high energy physics experiments. In this work, the efficiency and uniformity of gain of a prototype quad-GEM detector are studied. A simple method is used to estimate the efficiency with the help of an oscilloscope as a triggering and storage device. An efficiency of approximate to 95% is obtained at a voltage of Delta V-GEM >= 340V using cosmic muons as a source. A systematic study of the uniformity of gain over the active area of the detector is done with a Fe-55 X-ray source. The uniformity of gain has a spread of 11.1% over the active area of the quad-GEM detector for Delta V-GEM = 360 V. The effect of gas flow rate and direction of gas flow in determining the gain are investigated for the first time for a quad-GEM detector. It is observed that different flow rates does not affect the gain uniformity significantly. However, the overall gain of the detector initially increases with the gas flow rate and starts to saturate at a higher flow rate.