The Belle II diamond-detector for radiation monitoring and beam abort
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-06 |
| Journal | Proceedings of 40th International Conference on High Energy physics â PoS(ICHEP2020) |
| Authors | Y. Jin, K. Adamczyk, H. Aihara, T. Aziz, S. Bacher |
| Institutions | Université Paris-Saclay, Université Paris-Sud |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis technical analysis focuses on the successful implementation of synthetic Single-Crystal Diamond (SCD) sensors for critical radiation monitoring and preemptive beam abort systems at the SuperKEKB electron-positron collider (Belle II experiment).
- Critical Application: SCD sensors function as highly reliable solid-state ionization chambers, protecting sensitive inner detectors (PXD, SVD) from high beam-induced radiation resulting from SuperKEKBâs 50Ă increased luminosity target.
- Material Selection: High-purity, Chemical Vapour Deposition (CVD) grown Single-Crystal Diamond was selected specifically for its superior radiation hardness, rapid charge collection, and broad operational dynamic range (pA to mA).
- High-Speed Response: The system utilizes 28 SCD sensors and custom electronics (DCUs) featuring 50 MHz ADCs and FPGA logic to monitor instantaneous dose rates at 400 kHz.
- Preemptive Abort Logic: Two distinct dose thresholds (4 mrad in 10 ”s for bursts; 40 mrad in 1 ms for continuous increase) are implemented to trigger immediate beam aborts, preventing localized damage and magnet quenches.
- Performance Validation: The diamond system consistently provides the earliest abort signal among all beam loss monitors, proving essential for maintaining machine stability and achieving world-record instantaneous luminosity.
- Custom Fabrication: Sensors require precise metalization (Au/Pt/Ti stack) and high-quality SCD material, aligning perfectly with 6CCVDâs core manufacturing capabilities.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the key operational and performance parameters extracted from the Belle II diamond detector system:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Total Sensors Deployed | 28 | units | Located on the beam pipe, SVD support, and near focusing magnets. |
| Target Luminosity Increase | 50Ă | factor | Relative to predecessors KEKB and PEPII. |
| Inner Detector Dose Tolerance | 10 - 20 | Mrad | Maximum acceptable dose over a decade of operation. |
| Sensor Operational Range | pA to mA | A | Current proportional to radiation dose rate. |
| ADC Sampling Rate | 50 | MHz | Digitization frequency of front-end amplifiers. |
| Data Summation Rate | 400 | kHz | Rate at which 125 ADC values are summed in the FPGA buffer. |
| Abort Threshold 1 (Burst) | 4 | mrad | Dose integrated over 10 ”s (4 memory cells). |
| Abort Threshold 2 (Continuous) | 40 | mrad | Dose integrated over 1 ms (400 memory cells). |
| Typical Abort Frequency (Tuning) | ~10 | /hour | During machine studies and beam tuning phases. |
| Material Type | SCD | N/A | Synthetic Single-Crystal Diamond grown by CVD. |
| Electrode Metalization | Au/Pt/Ti | N/A | Used for charge collection and ohmic contact. |
Key Methodologies
Section titled âKey MethodologiesâThe Belle II diamond detector system relies on advanced material science and high-speed electronics integration to achieve its performance requirements:
- Material Growth: Synthetic Single-Crystal Diamond (SCD) is produced using the Chemical Vapour Deposition (CVD) technique, ensuring high purity necessary for detector-grade performance.
- Sensor Function: The SCD material operates as a solid-state ionization chamber, where incident radiation generates electron-hole pairs, resulting in a measurable current proportional to the dose rate.
- Electrode Fabrication: Custom metalization layers (Au/Pt/Ti stack) are deposited onto the SCD surface to form robust, low-resistance electrodes for charge collection.
- Signal Processing Chain: Signals are fed into custom front-end amplifiers offering three dynamic ranges, followed by digitization using Analog-to-Digital Converters (ADCs) at 50 MHz.
- High-Speed Abort Logic: A dedicated FPGA board processes the digitized data, calculating moving sums of dose rates every 2.5 ”s (400 kHz) and comparing these sums against two distinct, time-windowed thresholds.
- System Control: High voltages and amplifier dynamic ranges are configured via the FPGA, controlled by software implemented in the EPICS framework for large-scale control systems.
- Hand-Shaking Protocol: A robust hand-shaking procedure ensures the SuperKEKB control system confirms reception of the diamond abort signal, guaranteeing successful beam shutdown.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe Belle II diamond detector project demonstrates a critical need for high-quality, customized CVD diamond materials and precision fabricationâareas where 6CCVD excels. We are uniquely positioned to supply materials for replication, upgrades, or similar high-energy physics applications.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend the performance achieved in the Belle II experiment, 6CCVD recommends the following materials from our catalog:
| Material Specification | 6CCVD Product Line | Application Relevance |
|---|---|---|
| High Purity Single Crystal Diamond (SCD) | Detector Grade SCD | Essential for maximizing charge collection efficiency, ensuring rapid response, and guaranteeing extreme radiation hardness (required for 10-20 Mrad tolerance). |
| Polycrystalline Diamond (PCD) | High Purity PCD | Suitable for large-area monitoring applications where cost efficiency is prioritized, offering excellent radiation tolerance and thermal management. |
| Boron-Doped Diamond (BDD) | Heavy Boron Doped PCD/SCD | Ideal for electrochemical or high-conductivity applications, or as a robust, conductive substrate for complex detector architectures. |
Customization Potential
Section titled âCustomization Potentialâ6CCVDâs in-house fabrication capabilities directly address the specific requirements of advanced detector systems like Belle II:
- Custom Dimensions: While the paper implies small sensors, 6CCVD can supply SCD plates up to 500 ”m thick and PCD wafers up to 125mm in diameter, allowing for larger area coverage or future detector upgrades.
- Precision Metalization: We offer the exact electrode stack used in this research (Ti/Pt/Au) as a standard custom service. We also provide other common stacks (W, Pd, Cu) tailored to specific ohmic contact or bonding requirements.
- Surface Finish: 6CCVD guarantees ultra-low surface roughness, achieving Ra < 1nm for SCD and Ra < 5nm for inch-size PCD. This is crucial for uniform electric field application and reliable bonding in solid-state ionization chambers.
- Substrate Thickness: We can provide robust diamond substrates up to 10mm thick for mechanical support or heat spreading in high-power environments.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) to major research facilities worldwide, including KEK and associated institutions.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in optimizing CVD diamond for extreme environments, including high-energy physics and beam loss monitoring projects. We offer consultation services to assist engineers and scientists with:
- Material Selection: Determining the optimal diamond grade (SCD vs. PCD purity) based on required charge collection distance and noise floor.
- Electrode Design: Optimizing metalization thickness and geometry for specific impedance matching and bonding techniques.
- Radiation Hardness Testing: Providing materials with certified specifications suitable for multi-Mrad dose environments.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The SuperKEKB electron-positron collider at the KEK laboratory in Japan aims to achieve a maximum luminosity 50$\times$ higher than its predecessors KEKB and PEPII, positioning the Belle II experiment at the forefront of searches for non-standard-model physics in the next decade. High collision intensity implies high beam-induced radiation, which can damage essential Belle II sub-detectors and SuperKEKB components. Twenty-eight diamond sensors, read-out by purpose-built electronics, are installed in the interaction region to measure radiation and prevent damage. This talk introduces the system features and discusses its performance in early Belle II data taking.