Design and fabrication of low background, high energy resolution thermal bonding Micromegas detectors for the PandaX-III experiment

The high-pressure xenon time projection chamber (TPC) utilizing micro-pattern gaseous detector readout has emerged as a highly promising technical solution for the search of neutrino-less double beta decay events. This approach offers exceptional features, including high energy resolution, fine granularity, low background radioactivity, and scalability for large-scale experiments. In line with these advantages, the PandaX-III experiment aims to implement a 10 bar Xe-136 TPC, employing a readout plane comprising 52 194 x 194 mm(2) Micromegas detectors, within the China Jinping Underground Laboratory. To fulfill the stringent experimental requirements of PandaX-III, a low-background Micromegas detector with high energy resolution was proposed and developed using the thermal bonding method. The performance of the thermal bonding Micromegas prototypes was investigated using X-ray characterization under various gas mixtures with argon and isobutane from 1 bar to 10 bars. Remarkable results were presented at 1 bar gas pressure, where a maximum gas gain of similar to 8 x 10(4) and the best energy resolution (FWHM @5.9 keV) of 13.6% is obtained, and at 10 bar pressure, where maximum gas gain exceeding 10(4), the best energy resolution of 19%, and excellent stability over a test duration exceeding 150 h is achieved.