The spark rate measurement of resistive Micromegas for the ATLAS New Small Wheel upgrade

The New Small Wheel (NSW) will be installed on the ATLAS detector at CERN’s Large Hadron Collider (LHC) for stable operation in high luminosity environment. The NSW consists of two gaseous detectors, Resistive Micromegas (MM) and small-strip Thin Gap Chamber (sTGC). In MM detector, resistive anode is placed on copper read-out board to achieve its discharge resistance. In order to put the spark resistance into practice, ones must control anode resistivity which directly affecting performance of discharge suppressing. Previous study suggested the safety criteria for anode resistivity and the ATLAS’s MM mass production has been following the value, which is 20 +/- 200% [Mohm/cm/strip]. However, the detailed quantitative relation between spark resistance and anode resistivity is not fully understood. To achieve this, we measured spark rate of MM Read out board with different resistivity anodes.