High rate performance of Small-pad Resistive Micromegas. Comparison of different resistive protection concepts.

Motivated mainly by future detector upgrades at HL-LHC and at future colliders, mostof the HEP R&D; collaborations have been focusing on the design of new prototypes ofparticle detectors for operation under very high particle flow. In the field of Micro-Pattern-Gaseous-Detectors, the Small-pad resistive MICROMEGAS prototypes were designed toovercome the actual limitations of more standard strip resistive MICROMEGAS. In thesenew prototypes, small pads with a few mm$^{2}$ area replace the readout strips to reduce theoccupancy, and the spark protection resistive layer has been redesigned and optimizedwith different techniques to permit a safe behaviour of the detector, without efficiencyloss, at rates of the order of MHz/cm$^{2}$ over large surfaces. The firstly-developed designexploits a pad-patterned (PAD-P) embedded resistor layout by screen-printing while themost recent technique involves uniform sputtered DLC (Diamond Like Carbon structure)layers, where the current evacuates through vias to ground. Comparative studies havebeen conducted on the performances of the prototypes with different resistive layouts ordifferent values of DLC resistivity and vias pitch. The preliminary results of the tests donewith high-rate X-rays and with high energy charged particle beams will be presented.