Impact of the gas choice and the geometry on the breakdown limits in Micromegas detectors

Abstract

In this study we investigate the stability limits of Micromegas detectors upon irradiation with alpha particles. The results are obtained with meshes with different optical transparency and geometry of wires. The measurements are performed in Ar- and Ne- based mixtures with different CO2 content. We observe that the breakdown limit strongly depends on the gas and that a higher amount of quencher in the mixture does not necessarily correlate with higher stability. In addition, we observe discharge probability scaling with the wire pitch. This suggests that a Micromegas mesh cell can be treated as an independent amplification unit, similar to a hole in a GEM foil. The outcome of these studies provides valuable input for further optimization of MPGD detectors, multi-layer stacks in particular.

Towards development of Spark-Less-Avalanche-Microstructures

“…The transparency of the mesh for electrons 𝑇 el depends on the ratio 𝐸 drift /𝐸 trans of the electric fields above and below the mesh. It is measured to be close to 100 % for field ratios below 𝐸 drift /𝐸 trans ≤ 0.02 [5]. As a drift-shaping electrode, a PCB cathode is installed 26 mm above the mesh, defining the drift gap and field.…”