The paper describes a novel gaseous detector called MICROMEGAS, developed at Saclay. This detector is designed for high particle-flux environments and features a two-stage parallel-plate avalanche chamber with a small amplification gap (100 μm) and a conversion-drift space. The design allows for the rapid removal of positive ions produced during the avalanche process, enabling fast signals (≤ 1 ns) and high gas gains (up to 10^5). The detector's performance is characterized by its high rate capability, excellent spatial resolution, and stable gain over long irradiation periods. Key components include gold-coated copper anode strips, quartz spacers, a micromesh, and a conversion-drift electric field. The electric field configuration is optimized to achieve high electron transmission and efficient ion collection. Laboratory tests demonstrate the detector's ability to operate at high gains, with a rise time of about 200 ns and an energy resolution of 22% (FWHM). The authors conclude that MICROMEGAS combines high-resolution, cost-effectiveness, and the potential for very high counting rates, making it suitable for various applications.The paper describes a novel gaseous detector called MICROMEGAS, developed at Saclay. This detector is designed for high particle-flux environments and features a two-stage parallel-plate avalanche chamber with a small amplification gap (100 μm) and a conversion-drift space. The design allows for the rapid removal of positive ions produced during the avalanche process, enabling fast signals (≤ 1 ns) and high gas gains (up to 10^5). The detector's performance is characterized by its high rate capability, excellent spatial resolution, and stable gain over long irradiation periods. Key components include gold-coated copper anode strips, quartz spacers, a micromesh, and a conversion-drift electric field. The electric field configuration is optimized to achieve high electron transmission and efficient ion collection. Laboratory tests demonstrate the detector's ability to operate at high gains, with a rise time of about 200 ns and an energy resolution of 22% (FWHM). The authors conclude that MICROMEGAS combines high-resolution, cost-effectiveness, and the potential for very high counting rates, making it suitable for various applications.