[Paper Review] Signal Formation Processes in Micromegas Detectors and Quality Control for large size Detector Construction for the ATLAS New Small Wheel

F. Kuger|arXiv (Cornell University)|Aug 4, 2017

Particle Detector Development and Performance62 references3 citations

TL;DR

This paper investigates signal formation mechanisms in Micromegas detectors, focusing on electron loss and amplification processes through combined simulations, experiments, and theory. It establishes a rigorous quality control and assurance framework for large-scale production of Micromegas detectors for the ATLAS New Small Wheel upgrade, enabling reliable industrial-scale construction with optimized mesh and resistive anode PCBs.

ABSTRACT

The Micromegas technology is one of the most successful MPGD concepts and widely utilized in nuclear and particle physics experiments. Twenty years of research and development rendered the technology sufficiently mature to be selected as precision tracking detector for the New Small Wheel (NSW) upgrade of the ATLAS Muon spectrometer. This will be the first large scale application of Micromegas in one of the major LHC experiments. The studies on signal formation in Micromegas focuses on the microscopic signal electron loss mechanisms and the amplification processes in electron gas interaction. Based on a model of detector parameter dependencies, these processes are scrutinized in an iterating comparison between exper- imental results, theory prediction of the macroscopic observables and process simulation on the microscopic level. Utilizing the specialized detectors developed in the scope of this thesis as well as refined simulation algorithms, an unprecedented level of accuracy in the process description is reached, deepening the understanding of the fundamental process in gaseous detectors. The second part is dedicated to the challenges arising with the large scale Micro- megas production for the ATLAS NSW. A selection of technological choices, are discussed alongside a final report on two production related tasks addressing the detectors core components: For the industrial production of resistive anode PCBs a detailed quality control (QC) and quality assurance (QA) scheme as well as the therefore required testing tools have been developed. In parallel the study on micromesh parameter optimization and production feasibility resulted in the selection of the proposed mesh by the NSW community. The successful completion of both tasks were important milestones towards the construction of large size Micromegas detectors clearing the path for NSW series production.

Motivation & Objective

• To understand microscopic electron loss and amplification processes in Micromegas detectors for improved signal fidelity.
• To address the challenges of scaling Micromegas technology for large-scale production in the ATLAS New Small Wheel (NSW) experiment.
• To develop a comprehensive quality control and assurance (QC/QA) scheme for industrial production of resistive anode printed circuit boards (PCBs).
• To optimize micromesh parameters and validate production feasibility for large-size detector modules.
• To establish a validated, iterative model linking microscopic processes to macroscopic detector performance for gaseous detectors.

Proposed method

• Developed a multi-scale modeling approach combining microscopic process simulations with macroscopic observable predictions.
• Conducted experimental measurements using specialized detectors to validate theoretical and simulated signal formation behaviors.
• Implemented iterative comparison between simulation results, theoretical predictions, and experimental data to refine process understanding.
• Designed and tested dedicated QC/QA tools for resistive anode PCBs to ensure consistency and reliability in industrial production.
• Optimized micromesh geometry and production parameters through simulation and prototype testing.
• Established a production-ready process flow for large-size Micromegas detectors based on community-validated design choices.

Experimental results

Research questions

• RQ1 How do electron loss mechanisms and gas amplification processes affect signal formation in Micromegas detectors at the microscopic level?
• RQ2 What are the dominant factors influencing signal resolution and efficiency in large-area Micromegas detectors?
• RQ3 How can quality control and assurance be systematically implemented for industrial-scale production of Micromegas detectors?
• RQ4 What micromesh geometry and material parameters ensure optimal performance and manufacturability for large-size modules?
• RQ5 How can simulation models be calibrated against experimental data to achieve high-accuracy predictions of macroscopic detector behavior?

Key findings

• An unprecedented level of accuracy was achieved in modeling signal formation processes by integrating microscopic simulations, theoretical predictions, and experimental validation.
• The study revealed critical dependencies of electron loss and amplification on detector geometry, gas composition, and electric field configurations.
• A robust QC/QA framework was successfully developed for resistive anode PCB production, including dedicated testing tools for quality assurance.
• The micromesh design was optimized through simulation and prototype testing, leading to community-wide acceptance for NSW production.
• The integration of simulation, experiment, and iterative feedback enabled reliable prediction of macroscopic detector performance from microscopic physics.
• The completion of both QC/QA and mesh optimization tasks cleared critical technical hurdles for the start of series production of large-size Micromegas detectors in the ATLAS NSW.