Speaker
Description
The PICOSEC Micromegas detector is a precise-timing gaseous detector based on a Cherenkov radiator, a semi-transparent photocathode and a Micromegas amplification structure, targeting a time resolution of tens of picoseconds for minimum ionising particles. Single-pad prototypes have demonstrated excellent timing performance and ongoing developments aim to adapt the concept for physics applications by building robust, tileable multi-channel modules for large-area systems requiring precise timing.
Conventional photocathodes such as Cesium Iodide (CsI) provide high quantum efficiency and strong ultraviolet sensitivity, but are limited by their sensitivity to ion backflow, as well as humidity. These constraints motivate the development of more robust alternatives. While several materials have been previously explored, a comprehensive comparison of metallic and carbon-based photocathodes in terms of both time resolution and photoelectron yield was still missing.
This contribution presents a systematic study of photocathodes aimed at improving robustness while preserving excellent timing performance. Four materials with varing thcknesses - CsI, Titanium (Ti), Boron Carbide (B₄C) and Diamond-Like Carbon (DLC) - were produced at the CERN Thin Film and Glass and Micro-Pattern Technologies workshops. The photocathodes were characterised by combining laboratory measurements of their optical and resistive properties with beam tests using 150 GeV/c muons.
Although CsI is not suitable as a long-term solution, it remains a useful reference for detector and electronics studies. Investigations of few-nm CsI layers, supported by scanning electron microscopy measurements, show a grain-like morphology with grain size increasing with film thickness. For the beam measurements, the best result is obtained with a 5 nm CsI photocathode, achieving a time resolution of σ = 10.9 ± 0.3 ps with more than 30 extracted photoelectrons. Among the alternative materials, Ti and B₄C show the most promising outcome, reaching σ ≈ 30 ps with approximately 5 photoelectrons. Current work focuses on exploring alternative photocathode configurations, enabled by the versatility of magnetron sputtering.
The results demonstrate that improved robustness can be achieved while maintaining excellent time resolution, supporting the feasibility of using the PICOSEC Micromegas concept in future experiments.
| Name of the speaker | Marta Lisowska |
|---|---|
| Eligible for the Georges Charpak Young Scientist Award. | yes |