Research Information System
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol.1090, 2026 (SCI-Expanded, Scopus)
The PICOSEC Micromegas detector is a Micro-Pattern Gaseous Detector (MPGD) concept developed to achieve tens of picosecond-level timing resolution for charged particle detection by combining a Cherenkov radiator with a two-stage Micromegas amplification structure. To improve operational robustness at high gain and under intense radiation backgrounds, a resistive anode has been implemented using a diamond-like carbon (DLC) layer deposited on a Kapton substrate. While this design enhances detector stability, the resistive layer may influence rate capability, signal formation, and detector capacitance, altering its timing performance.x In this work, a comprehensive study of a resistive PICOSEC design is presented, including an analytical model and finite-element simulation to quantify rate-dependent gain reduction due to ohmic voltage drop in the resistive layer. An analytical solution for the voltage distribution across a finite-size resistive layer is derived, and a numerical model is developed to evaluate gain suppression under intense particle fluxes. For the single-channel prototype geometry and expected beam conditions at the CERN SPS H4 beam line, surface resistivities around 20 MΩ/□ are found to ensure discharge protection and acceptable gain stability. The impact of the resistive layer on signal integrity is investigated using an extended Ramo–Shockley formalism with time-dependent weighting fields and Garfield++ simulations. The contribution of delayed signal components induced by the resistive layer is quantified, and a preservation of the leading-edge of the signal was found for surface resistivities exceeding 100 kΩ/□. Single-channel resistive-anode prototypes were designed (∅10 and ∅15 mm), constructed, and experimentally characterized. Laboratory measurements using single photoelectrons and a power spectral density analysis show the predicted reduction in signal amplitude due to the insulating layer, while preserving the leading edge of the electron peak. Muon beam tests with both CsI and DLC photocathodes were performed. They demonstrate a time resolution of 11.5±0.4 ps using CsI, comparable to the 11.9±0.4 ps of the metallic-anode device, showing the suitability of the resistive design for precision timing applications in challenging operational conditions.