Diamond Detectors for Radiation Monitoring and Beam Abort at Belle II
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | Acta Physica Polonica B |
| Authors | R. Manfredi |
| Institutions | Campbell Collaboration, Istituto Nazionale di Fisica Nucleare, Sezione di Trieste |
| Citations | 1 |
| Analysis | Full AI Review Included |
Diamond Detectors for Radiation Monitoring and Beam Abort at Belle II
Section titled âDiamond Detectors for Radiation Monitoring and Beam Abort at Belle IIâExecutive Summary
Section titled âExecutive Summaryâ- Core Technology: The Belle II radiation monitoring and beam-abort system utilizes 28 synthetic single-crystal diamond sensors, functioning as highly radiation-resistant solid-state drift chambers.
- Protection Mandate: The system is critical for protecting the inner vertex detector (VXD), which has a maximum tolerance of 10-20 Mrad over a decade, from intense beam-background radiation spikes.
- Critical Performance Metric: The system must detect and trigger an abort for high-dose spikes (1 rad or more) delivered in less than 1 millisecond (ms) to prevent localized damage.
- Material Advantages: Diamond was chosen for its exceptional radiation resistance, ensuring stable long-term operation, and its rapid response time, crucial for detecting sudden radiation bursts.
- Operational Range: The sensors provide a broad dynamic range, capable of measuring dose rates from low levels (”rad/s) up to extreme levels (O(10) krad/s).
- System Optimization: A significant firmware upgrade reduced the delay in the beam-abort chain by increasing the abort logic sampling rate from 100 kHz to 400 kHz, shortening the integration gate to 2.5 ”s.
- Operational Impact: During 2019 physics operations, the diamond system successfully issued approximately 300 beam aborts, primarily concentrated during machine study periods, ensuring safe and efficient data collection.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material | Synthetic Single-Crystal Diamond | N/A | Sensor type (Solid-state drift chamber) |
| Total Sensors | 28 | N/A | Installed around the beam pipe and SVD structure |
| Sensor Bias Voltage | O(100) | V | Applied for electron-hole pair collection |
| Vertex Detector Dose Tolerance | 10 - 20 | Mrad | Maximum dose over a decade of operation |
| Critical Radiation Spike | 1 | rad | Dose causing localized damage if delivered in < 1 ms |
| Dose Rate Range (High) | O(10) | krad/s | Maximum rate detectable by the system |
| ADC Oversampling Rate | 50 | MHz | Raw digitization rate |
| Abort Logic Sampling Rate (2019) | 100 | kHz | Data stream rate for abort decision |
| Abort Logic Sampling Rate (Upgrade) | 400 | kHz | Improved rate for reduced delay (2.5 ”s integration) |
| Abort Logic Integration Gate (2019) | 10 | ”s | Moving sum window length |
| Monitoring Data Output Rate | 10 | Hz | Used for online/offline radiation monitoring |
| Belle II Integrated Luminosity Goal | 50 | ab-1 | Target luminosity by 2029 |
| Beam Abort Signal Transmission | 700 | m | Fibre-optic cable length to SuperKEKB control room |
Key Methodologies
Section titled âKey Methodologiesâ- Charge Carrier Generation: The diamond sensor functions as a solid-state drift chamber. Traversing charged particles generate free electron-hole pairs within the crystal lattice.
- Signal Collection: A bias voltage of O(100)V is applied to the metallic ends of the sensor, causing the generated electron-hole pairs to drift and be collected, producing a time-dependent current proportional to the dose rate.
- Signal Processing Chain: The current is amplified by a trans-impedance amplifier, digitized, and oversampled at 50 MHz by ADCs.
- High-Rate Data Stream Creation: The 50 MHz samples are summed in blocks (N1 = 500) to create the 100 kHz (or 400 kHz post-upgrade) data stream used for the fast beam-abort logic.
- Real-Time Dose Integration: The FPGA runs two independent moving sums (âgatesâ) on the high-rate data stream, integrating the dose over short, configurable time windows (e.g., 2.5 ”s or 10 ”s).
- Abort Triggering: If the integrated dose in either moving sum exceeds its corresponding pre-set threshold, an immediate beam-abort request signal is generated.
- Beam Dump Execution: The abort request is transmitted via a 700 m fibre-optic cable, combined with signals from other accelerator monitors, and used to activate the kicker magnets, which rapidly dump the beams.
- System Optimization and Monitoring: A separate 10 Hz data stream (summed in blocks of 104) is used for online and offline monitoring, allowing correlation studies between radiation doses and accelerator parameters (e.g., beam currents, collimator openings).
Commercial Applications
Section titled âCommercial Applicationsâ- High-Energy Physics (HEP) and Accelerator Facilities: Essential for beam loss monitoring (BLM), fast beam position monitoring, and radiation protection systems in high-luminosity colliders (e.g., CERN, KEK).
- Nuclear and Medical Dosimetry: Diamondâs high radiation hardness and near tissue-equivalent properties make it ideal for precise, stable measurement of high-dose radiation fields in cancer therapy (radiotherapy) and nuclear reactor environments.
- Space and Defense Systems: Used as radiation-hard sensors and detectors in satellites, spacecraft, and military applications where electronics must survive high fluxes of cosmic rays and charged particles.
- Fusion Energy Research: Monitoring neutron and particle fluxes in extreme environments, such as magnetic confinement fusion reactors (e.g., ITER), where high temperatures and intense radiation rapidly degrade conventional semiconductor materials.
- High-Power Electronics and RF: Integration of diamond sensors into high-power microwave or radar systems for real-time monitoring of radiation and thermal stress, leveraging diamondâs superior thermal management properties.
View Original Abstract
The Belle II experiment will be at the forefront of indirect searches for non-Standard-Model physics using billions of heavy quarks and $\tau$ leptons produced in high-intensity 10 GeV electron-positron collisions from the SuperKEKB collider. The intense beams needed to achieve the required precisions are associated with high beam-background radiation that may damage the inner detectors. A dedicated radiation-monitoring and beam-abort system, based on artificial diamond sensors, ensures protection and safe data taking conditions. I briefly outline the system and illustrate the operational experience and performance during 2019 physics operations.