Development of the BCM system and readout for ATLAS
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-02-05 |
| Authors | Ignacio Asensi Tortajada, Adrien Baptiste, B. Hiti, H. Kagan, H. Frais-Kölbl |
| Institutions | Fachhochschule Wiener Neustadt, University of Manchester |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe BCMâ (Beam Conditions Monitoring prime) system is a critical upgrade for the ATLAS Inner Tracker (ITk) at the High-Luminosity LHC (HL-LHC), designed to safeguard inner detectors and monitor luminosity under extreme radiation conditions.
- Core Technology: The system utilizes radiation-hard polycrystalline Chemical Vapor Deposition (pCVD) diamond sensors segmented for dual functionality: high-efficiency beam abort triggering and precise luminosity measurement.
- Radiation Tolerance: The custom Calypso Front-End (FE) ASIC (TSMC 65 nm process) is engineered to withstand a Total Ionizing Dose (TID) of up to 3 MGy, meeting HL-LHC requirements.
- High-Speed Readout: The Calypso ASIC provides semi-digital LVDS output with a 1 ns rise time and 200 ps jitter, enabling Time-of-Flight (ToF) measurements crucial for discriminating collision events from upstream background noise.
- Data Acquisition Chain: Data is transmitted optically at 1.28 Gbps via Opto Boards and processed by the FPGA-based ATLAS FELIX system, which calculates Time-over-Threshold (ToT) and Time-of-Arrival (ToA) for every signal.
- Performance Validation: Preliminary beam tests using a 120 GeV pion beam demonstrated a high signal-to-noise ratio (25 at ±1000 V) and an efficiency greater than 99% for multi-Minimum Ionizing Particles (MIPs).
- System Functionality: The FELIX firmware is designed to package ToT/ToA data with proper Bunch Crossing ID (BCID) and Level 1 Accept (L1A) tagging, and is slated to implement the analog beam abort signal functionality shortly.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| ASIC Process Node | 65 | nm | Calypso_D Front-End ASIC (TSMC) |
| TID Tolerance (ASIC) | Up to 3 | MGy | Total Ionizing Dose rating for Calypso |
| ASIC Die Size | 2 x 2 | mm2 | Minimal die size of Calypso_D |
| Sensor Material | Polycrystalline | CVD Diamond | Detector material (500 ”m thick) |
| Sensor Segmentation | 10 x 10 and 5 x 5 | mm2 | Luminosity and beam abort functions, respectively |
| Signal-to-Noise Ratio (SNR) | 25 | N/A | Measured at ±1000 V bias |
| Detection Efficiency | > 99 | % | For multi-MIPs at 5Ï threshold |
| Front-End Noise | 200 | e- | Calypso ASIC specification |
| Time Jitter | 200 | ps | Calypso ASIC specification |
| Signal Rise Time | 1 | ns | Calypso ASIC specification |
| Detector Capacitance | 2 | pF | Input capacitance specification |
| Data Link Rate (Optical) | 1.28 | Gbps | LAPA driver to Opto Board transmission |
| BCMâ Ring Z Position | ±1.875 | m | Distance from interaction point (6.25 ns) |
| Upstream Signal Time Offset | ~12.5 | ns | Time-of-Flight difference (t â -2z/c) |
Key Methodologies
Section titled âKey MethodologiesâThe BCMâ system development and testing followed a rigorous methodology integrating radiation-hard materials, custom electronics, and high-speed data processing.
- Sensor Segmentation and Integration: pCVD diamond sensors were segmented into two sizes (10x10 mm2 and 5x5 mm2) to optimize performance for distinct tasks: luminosity monitoring (single-MIP sensitivity) and beam abort triggering (multi-MIP sensitivity).
- Front-End Signal Processing: The Calypso FE ASIC was used to process sensor signals, applying gain and Constant Fraction Discriminator (CFD) settings. It converts the analog charge signal into a semi-digital LVDS output, where the duration of the high state represents Time-over-Threshold (ToT) and the timing represents Time-of-Arrival (ToA).
- High-Speed Data Transmission: Signals were amplified by radiation-hard LAPA drivers and transmitted over 5 m of Twinax cable to Opto Boards. The Opto Boards converted the electrical signals into optical signals at 1.28 Gbps, encapsulated in LPGBT frames for long-distance transmission to the services cavern.
- FPGA-Based Readout (FELIX): The ATLAS Front-End Link eXchange (FELIX) system continuously processes the incoming optical data. A custom decoding block, leveraging ITk Pixel firmware architecture, calculates ToT and ToA relative to a 40 MHz clock, ensuring proper BCID and L1A tagging.
- Zero Suppression and Data Formatting: The FELIX firmware includes a zero-suppression flag and formats the data into variable-size fragments (32-bit chunks), ensuring data integrity and efficient transmission to the next element in the readout chain.
- Beam Test Validation: Preliminary system validation was performed at the H6 SPS beam line at CERN using a 120 GeV pion beam. A MALTA telescope provided precise tracking and timing references (4.1 ”m spatial resolution, 2.1 ns timing resolution) to verify the accuracy of the Calypso ToT and ToA measurements.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology developed for the BCMâ system, centered on radiation-hard diamond detectors and high-speed, low-power ASICs, is applicable across several high-reliability and extreme environment sectors.
- High-Energy Physics: Direct application in future collider upgrades (e.g., HL-LHC) for beam monitoring, luminosity measurement, and machine protection systems.
- Space and Aerospace: Utilization of radiation-hard pCVD diamond sensors and electronics for satellite instrumentation, space probes, and high-altitude atmospheric monitoring where high TID tolerance is mandatory.
- Medical Dosimetry: Development of high-precision, real-time radiation monitors for cancer therapy (e.g., proton or carbon ion therapy), leveraging the diamondâs tissue equivalence and stability.
- Nuclear and Fusion Research: Deployment in harsh radiation environments (e.g., ITER, fission reactors) for real-time flux monitoring, beam profile measurement, and safety interlocks.
- Industrial Accelerator Facilities: Use in industrial particle accelerators for quality control, material modification, and non-destructive testing, requiring robust, high-rate beam diagnostics.
View Original Abstract
The High Luminosity upgrade of the Large Hadron Collider will increase the LHC luminosity and with it the density of particles on the detector by an order of magnitude. For protecting the inner silicon detectors of the ATLAS experiment and for monitoring the delivered luminosity, a radiation hard beam monitor has been developed. A set of detectors has been developed based on polycrystalline Chemical Vapor Deposition diamonds and a new dedicated radiation-hard front-end ASIC. To satisfy the requirements imposed by the HL-LHC, our solution is based on segmenting diamond sensors into devices of varying size and reading them out with new multichannel readout ASICs divided into two independent parts, each of them serving one of the tasks of the system. This document describes the system design including detectors, electronics and the ATLAS FPGA FELIX based readout. Additionally, it presents preliminary results of the readout with data from beam tests from 2023 at the SPS beam line at CERN.