A MIDAS-based Data Acquisition System for Gaseous Detectors

This paper presents a comprehensive, web-enabled data acquisition system based on the MIDAS framework for gaseous detectors, which has been successfully deployed and validated in the PandaX-III experiment to support real-time monitoring and a unified workflow from data acquisition to offline analysis.

The Gist

Imagine you are trying to listen to a massive choir of 6,656 singers (the detector channels) all at once, trying to catch a single, tiny whisper (a rare particle event) in a noisy stadium. If you just let them all shout into a single microphone, you'd get a mess of static. You need a super-smart, super-fast conductor and a recording studio that can instantly sort, label, and save every note, while letting you watch the performance on a screen in real-time.

This paper is about building that super-conductor and recording studio for a specific type of scientific instrument called a Gaseous Detector.

Here is the breakdown of what they built, using simple analogies:

1. The Problem: The "Too Many Cooks" Situation

Scientists use gas-filled chambers (like giant, high-tech cloud chambers) to track particles. When a particle zips through the gas, it leaves a trail of electrical signals.

• The Challenge: The PandaX-III experiment (the project this software helps) has a detector with 6,656 separate "ears" (channels) listening for these signals.
• The Old Way: Usually, managing that many ears requires complex, rigid computer systems that are hard to tweak. If you want to change how loud the "microphones" are, you might have to rewrite code or restart the whole system.
• The Goal: They needed a system that is flexible, fast, and easy to control from a web browser, like a modern smart home app.

2. The Solution: The "MIDAS" Framework

The team built their system using a software framework called MIDAS. Think of MIDAS as a universal operating system for scientific experiments. It's like Android or iOS for particle physics. It comes with built-in tools for:

• The Dashboard: A web page where you can see everything happening.
• The Logbook: Automatically writing down what happened and when.
• The Storage: Saving the data safely.

They customized this "operating system" specifically for their gas detector, creating a custom app that handles the unique needs of listening to 6,000+ channels.

3. How It Works: The "Traffic Control" System

The system is divided into three main layers, like a postal service:

• The Front-End (The Mail Collectors): These are the chips (called AGET) right next to the detector. They catch the raw electrical signals. They are like mail carriers picking up letters from houses. They can be told to ignore empty envelopes (noise) to save space.
• The Back-End (The Sorting Facility): This is the "Back-End Card" (BEC). It collects the mail from all the carriers, organizes it into bundles (events), and sends it to the main computer. It has two ways to talk to the main computer: via a fast USB cable or a network cable (like the internet).
• The DAQ Software (The Central Post Office): This is the brain. It receives the bundles, checks them for errors, and saves them to a hard drive.
  • The Web Interface: This is the control room. Scientists can sit at a laptop, open a browser, and see a live map of where the particles are hitting. They can pause, stop, or restart the experiment with a click.
  • Real-Time Monitoring: It's like watching a live sports broadcast. You can see the "score" (energy spectrum) and the "player positions" (hit maps) instantly, not hours later.

4. The "Smart" Features

The software isn't just a recorder; it's an intelligent assistant:

• Dynamic Range (The Volume Knob): Sometimes the signal is a whisper (low energy), sometimes a shout (high energy). The software can instantly switch the "volume" settings so it doesn't miss the whisper or get blown out by the shout.
• Channel Compression (The Noise Filter): If 6,000 channels are mostly silent, why record all that silence? The software can be told, "Only record the channels that actually heard something." This saves massive amounts of computer space.
• The REST Connection: This is a special bridge that connects the recording system directly to the analysis tools. It's like having the recording studio directly wired to the editing suite. As soon as data is recorded, it's ready to be analyzed, turning raw numbers into scientific discoveries much faster.

5. The Proof: Did It Work?

The team tested this system in two ways:

1. The "Fake" Test: They used a signal generator (a machine that makes fake electrical sounds) to see if the system could handle the speed. It worked perfectly, handling 230 events per second with zero data loss, even after running for a month straight.
2. The "Real" Test: They hooked it up to the actual PandaX-III detector prototype. They used radioactive sources (like tiny, safe X-ray flashlights) to see if the system could map where the particles hit.
   • Result: The system successfully created clear maps (hitmap) showing exactly where the particles landed and measured their energy perfectly. It worked with just one module and also with a massive setup of seven modules.

The Bottom Line

This paper describes a user-friendly, high-speed, and flexible recording system for a giant particle detector.

Before this, setting up such a detector was like trying to conduct an orchestra with a tangled mess of wires and no sheet music. Now, with this MIDAS-based software, scientists have a digital conductor that lets them tune the instruments, watch the performance live, and instantly save the best parts of the show, all from a simple web browser. This makes it much easier to hunt for rare cosmic events, like the "ghostly" particles they are looking for in the PandaX-III experiment.

Technical Summary

1. Problem Statement

Gaseous detectors, particularly Time Projection Chambers (TPCs), are critical for particle, nuclear, and astroparticle physics experiments (e.g., dark matter searches and neutrinoless double beta decay). However, they present significant challenges for Data Acquisition (DAQ) systems due to:

• Scale and Complexity: Experiments like PandaX-III require massive readout systems (e.g., 6,656 channels across 52 Micromegas modules).
• Dual Requirements: Systems must balance high imaging accuracy (requiring precise 3D spatial and energy reconstruction) with the ability to handle large data volumes.
• Integration Gaps: Traditional DAQ solutions often lack seamless integration between real-time monitoring, parameter configuration, and offline analysis, leading to compatibility issues and inefficient workflows.
• Specific Needs: There is a need for a unified, robust, and flexible software framework capable of handling diverse electronics setups (different back-end modules) while providing real-time visualization and alarm capabilities.

2. Methodology

The authors developed a comprehensive DAQ software solution based on the MIDAS (Maximum Integrated Data Acquisition System) framework, specifically tailored for gaseous detectors. The methodology involves:

• Architecture Design:
  • Framework: Built on MIDAS, utilizing its core applications (odbedit, mhttpd, mlogger) for parameter management, web interaction, and data logging.
  • Custom Modules: Developed two custom applications:
    • CmdProc: For monitoring command configurations and receiving feedback from backend electronics.
    • DataFlow: Responsible for receiving raw data frames, parsing them, and reconstructing events.
  • Communication: Supports two distinct communication protocols to interface with different back-end electronics (BEC):
    • USB 3.0: Used with the DCM (Data Concentration Module) for high-speed transmission (up to 1.6 GB/s theoretical).
    • UDP over Ethernet: Used with the TDCM (Trigger and Data Concentration Module) for low-latency, connectionless streaming.
• Data Handling:
  • Format: Implements a hierarchical event structure (Event Header, Global Bank Header, Data Banks) where each bank corresponds to a specific channel.
  • Storage: Data is stored in LZ4 compressed format via a ring buffer to support concurrent read/write operations.
  • Integration: Seamlessly interfaces with the REST (Rare Event Searches Toolkit) framework, allowing for real-time waveform visualization, energy spectrum analysis, and immediate data decoding during acquisition.
• User Interface: A web-based interface allows for:
  • Real-time monitoring of system status, event rates, and alarms.
  • Dynamic parameter configuration (e.g., trigger modes, sampling rates, gain settings) via an Online Database (ODB) using hot-linking mechanisms.
  • One-click global configuration via XML files for standardized testing.

3. Key Contributions

• Unified Workflow: Established a fully integrated workflow spanning from data acquisition to offline analysis, eliminating the need for manual data conversion between acquisition and reconstruction stages.
• Hardware Agnosticism: Successfully adapted to two distinct electronics setups (TDCM and DCM) used in the PandaX-III experiment, demonstrating high versatility.
• Real-Time Capabilities: Enabled real-time visualization of signal waveforms and energy spectra, allowing researchers to dynamically adjust experimental parameters (e.g., trigger delays, sampling rates) based on live data quality.
• Advanced Triggering & Compression: Implemented flexible trigger modes (Self-Trigger, Hit Trigger, Multiplicity Trigger) and intelligent channel compression algorithms to optimize bandwidth usage by filtering out noise-dominated channels.
• Scalability: Designed to handle the massive channel count of the PandaX-III detector (6,656 channels) while maintaining stability.

4. Results

The system was validated through extensive testing involving signal generators, single readout modules, and a prototype detector with seven modules:

• Performance Metrics:
  • Event Rate: Achieved a maximum event rate of 230 Hz for a single AGET chip full readout.
  • Data Transfer: Sustained a data transfer rate of 15.2 MB/s.
  • Stability: Operated continuously for 30 days with negligible data packet loss or corruption.
• Functional Validation:
  • Successfully demonstrated adjustable sampling rates (5 MHz to 100 MHz) and trigger delays.
  • Validated channel compression features, showing significant bandwidth savings when noise channels were suppressed.
  • Accurately reconstructed waveforms for calibration sources ($^{37}$Ar and $^{109}$Cd) under various gas pressures and electric fields.
• Detector Integration:
  • Successfully mapped 2D hit positions and energy spectra for both single-module and seven-module configurations.
  • Correctly identified electronic bad channels and electric field distortions at the edges of the readout plane.
  • Validated the system's ability to handle the specific requirements of the PandaX-III experiment, including the 10 bar argon/isobutane gas mixture environment.

5. Significance

This work provides a robust, scalable, and user-friendly DAQ solution that addresses the critical bottlenecks in gaseous detector experiments.

• Operational Efficiency: The web-based interface and real-time monitoring significantly reduce the time required for system commissioning and parameter tuning.
• Scientific Impact: By integrating directly with the REST analysis framework, the system accelerates the path from raw data to physical insights, which is crucial for rare event searches like neutrinoless double beta decay.
• Reproducibility and Flexibility: The modular design allows the software to be easily adapted to other gaseous detector experiments with different electronics or channel counts, serving as a reference architecture for future large-scale physics experiments.
• Validation: The successful deployment in the PandaX-III experiment confirms the system's readiness for high-stakes, long-duration physics runs.