Small-Pad Resistive Micromegas: rate capability for different spark protection resistive schemes

Started few years ago, the goal of this R&D project is to develop a new generation of single amplification stage resistive MPGD based on Micromegas technology with the following characteristics: stable and efficient operation up to 10 MHz/cm(2) particle flows; high granularity readout with small pads of the order of mm(2); reliable and cost-effective production process. The miniaturization of the readout elements and the optimization of the spark protection system, as well as the stability and robustness under operation, are the primary challenges of the project. Several Micromegas detectors have been built with similar anode planes, segmented with a matrix of 48 x 16 readout pads with a rectangular shape (0.8 x 2.8 mm(2)) and with a pitch of 1 and 3mm in the two coordinates. The active surface is 4.8 x 4.8 cm(2) with a total number of 768 channels, routed off-detector for readout. With this anode/readout layout, the spark protection resistive layer has been realized with two different techniques: a pad-patterned embedded resistor with screen printing, and a uniform DLC (Diamond Like Carbon structure) layer by sputtering. For each technique different configurations and resistivity values have been adopted. For the DLC series, the most recently built prototype exploits the availability of copper clad DLC foils to improve the construction. Characterization and performance studies of the detectors have been carried out by means of radioactive sources, X-Rays, and test beam. A comparison of the performance obtained with the different resistive layout and different configurations are presented, in particular focusing on the response under high irradiation and high rate exposure.