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-Sud, Université Paris-Saclay |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on the Belle II diamond detector system, designed to protect the SuperKEKB electron-positron collider and its inner detectors (PXD, SVD) from high beam-induced radiation.
- Core Value Proposition: The system provides ultra-fast, radiation-hard monitoring and beam abort capabilities essential for achieving and sustaining the target luminosity (50x greater than predecessors).
- Material Choice: Synthetic single-crystal diamond (sCVD) sensors are used due to their superior radiation hardness, rapid response time, and broad dynamic range (pA to mA).
- Protection Mechanism: The system employs a dual-threshold logic implemented in an FPGA to detect two types of radiation events: fast, high-intensity bursts and slower, continuously increasing radiation.
- Fast Abort Logic: Triggers an immediate beam abort if the dose exceeds 4 mrad within a 10 ”s window, protecting against sudden spikes.
- Slow Abort Logic: Triggers an abort if the dose exceeds 40 mrad within a 1 ms window, protecting against continuous dose accumulation and potential magnet quenches.
- Performance: The diamond system successfully triggered 655 beam aborts during the 2020 running period, frequently acting as the fastest source of abort signals received by the SuperKEKB control room.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Luminosity Increase | 50x | N/A | Compared to KEKB and PEPII. |
| Inner Detector Dose Tolerance | 10-20 | Mrad | Maximum dose over a decade (PXD/SVD). |
| Sensor Material Type | sCVD | N/A | Synthetic Single-Crystal Diamond (Element Six). |
| Electrode Composition | Au/Pt/Ti | N/A | Used for solid-state ionization chamber operation. |
| Sensor Current Range | pA to mA | Current | Proportional to radiation dose rate. |
| Total Sensors Installed | 28 | N/A | 8 on beam pipe, 12 on SVD support, 8 near magnets. |
| ADC Sampling Rate | 50 | MHz | Digitization frequency of front-end amplifier output. |
| Data Summing Rate | 400 | kHz | Rate at which 125 ADC values are summed into memory cells. |
| FPGA Buffer Size | 4 | Gbit | Revolving buffer memory capacity. |
| Moving Sum Update Frequency | 2.5 | ”s | Time interval for comparing sums against thresholds. |
| Fast Abort Threshold (Burst) | 4 | mrad | Dose integrated over 10 ”s (4 memory cells). |
| Slow Abort Threshold (Continuous) | 40 | mrad | Dose integrated over 1 ms (400 memory cells). |
| Slow Monitoring Rate | 10 | Hz | Rate for calculating and transmitting integrated dose (sum of 40000 cells). |
Key Methodologies
Section titled âKey Methodologiesâ- Sensor Manufacturing: Synthetic single-crystal diamond (sCVD) sensors were produced using Chemical Vapour Deposition (CVD) techniques (Element Six), followed by the application of Au/Pt/Ti electrodes (CIVIDEC).
- Signal Conditioning: Front-end amplifiers were designed with three distinct dynamic ranges to accurately measure currents spanning from pA to mA, accommodating the wide variation in beam-induced radiation rates.
- High-Speed Data Acquisition: Signals were digitized by Analog-to-Digital Converters (ADCs) at a 50 MHz sampling rate. These values were then summed into memory cells at a 400 kHz rate.
- Real-Time Abort Logic (FPGA): The FPGA continuously calculated moving sums of the memory cell values, updating the comparison against thresholds every 2.5 ”s.
- Dual-Threshold Abort Implementation:
- Radiation Burst Abort: Triggered by integrating the dose over a short 10 ”s window (4 memory cells) against a 4 mrad threshold.
- Continuous Radiation Abort: Triggered by integrating the dose over a longer 1 ms window (400 memory cells) against a 40 mrad threshold.
- Control and Readout: The system utilized the EPICS framework for large-scale control, managing amplifier dynamic ranges, high voltages, and transmitting slow monitoring data (10 Hz) via Ethernet.
- Abort Hand-Shaking: A confirmation procedure was established with the SuperKEKB control system, ensuring the diamond system continued firing the abort signal until reception was acknowledged, guaranteeing successful beam termination.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology developed for the Belle II diamond detector leverages the unique properties of sCVD diamond, making it highly relevant for applications requiring extreme radiation hardness, fast response, and high stability.
- High Energy Physics (HEP) and Accelerator Science:
- Primary beam loss monitoring (BLM) in high-luminosity colliders (e.g., LHC, future linear colliders).
- Fast beam abort systems for protecting sensitive superconducting magnets and detector components.
- Nuclear and Fusion Energy:
- In-situ radiation monitoring and dosimetry within high-flux environments (e.g., ITER, advanced fission reactors) where silicon-based detectors rapidly degrade.
- Space and Defense:
- Radiation detection and dosimetry for satellites and spacecraft, utilizing diamondâs intrinsic resistance to displacement damage and temperature stability.
- Medical Physics and Radiotherapy:
- High-dose-rate monitoring for advanced cancer treatments (e.g., proton therapy, heavy ion therapy).
- Real-time quality assurance for beam delivery systems requiring sub-microsecond response times.
- Industrial Beam Processing:
- Monitoring and control of high-power electron or X-ray beams used for sterilization, material modification, and non-destructive testing.
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.