Diamond Detectors for Radiation Monitoring and Beam Abort at Belle II

At a Glance

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 High-Intensity Radiation Monitoring (Belle II)

This technical documentation analyzes the requirements for synthetic diamond sensors used in the Belle II radiation monitoring and beam abort system, highlighting how 6CCVD’s advanced MPCVD capabilities meet and exceed these demanding specifications for High Energy Physics (HEP) applications.

Executive Summary

Application Criticality: Synthetic Single-Crystal Diamond (SCD) sensors are essential for protecting the sensitive inner detectors and superconducting magnets of the high-luminosity SuperKEKB/Belle II collider from intense beam-background radiation.
Material Selection: The system relies on 28 high-purity SCD sensors, chosen specifically for their superior radiation resistance, ensuring reliable operation over the detector’s expected decade-long lifetime (tolerating 10-20 Mrad).
Rapid Response Requirement: Diamond’s rapid response time is critical for detecting sudden, intense radiation spikes (1 rad or more in < 1 ms) and initiating a beam abort sequence.
System Performance: The detectors monitor a broad dynamic range of dose rates, spanning from µrad/s up to O(10) krad/s, corresponding to currents from pA to mA.
Timing Optimization: The beam-abort logic was recently upgraded, increasing the sampling rate from 100 kHz to 400 kHz, reducing the delay between threshold crossing and abort trigger to 2.5 µs.
6CCVD Value Proposition: 6CCVD specializes in providing the high-purity, custom-dimensioned SCD wafers and precision metalization required for next-generation radiation detection and fast timing applications.

Technical Specifications

The following hard data points were extracted from the analysis of the Belle II diamond detector system:

Parameter	Value	Unit	Context
Detector Material	Synthetic Single-Crystal Diamond (SCD)	N/A	Used for radiation monitoring and beam abort
Total Sensors Deployed	28	Units	Installed around the beam pipe and SVD structure
Operating Bias Voltage	O(100)	V	Applied across metallic contacts for charge collection
Vertex Detector Tolerance	10 - 20	Mrad	Maximum dose over a decade of operation
Critical Radiation Spike	1 or more	rad	Dose capable of localized damage in < 1 ms
Dose Rate Monitoring Range	µrad/s to O(10) krad/s	N/A	Corresponds to current range from pA to mA
ADC Oversampling Rate	50	MHz	Digitization of amplified diamond currents
Abort Logic Sampling Rate (Upgraded)	400	kHz	Comparison rate for thresholds (2.5 µs comparison interval)
Integrated Luminosity Goal	50	ab^-1	Target for Belle II experiment by 2029
Peak Luminosity (2019)	1.14 x 10³⁴	cm^-2s^-1	Achieved during 2019 operations

Key Methodologies

The Belle II radiation monitoring system relies on the intrinsic properties of high-purity SCD coupled with high-speed digital processing:

Charge Generation: Traversing charged particles interact with the SCD lattice, generating free electron-hole pairs.
Charge Collection: An applied bias voltage of O(100)V causes the electron-hole pairs to drift rapidly, functioning as a solid-state drift chamber.
Signal Amplification: The resulting time-dependent current is fed into a trans-impedance amplifier to boost the signal.
High-Speed Digitization: The amplified current is digitized and oversampled by ADCs at 50 MHz.
Abort Logic Data Stream: The 50 MHz samples are summed in blocks (N1 = 500) to create a 100 kHz data stream (later upgraded to 400 kHz) for real-time abort decision-making.
Dynamic Integration: Two different moving sums (gates) run on the high-speed data stream, integrating the dose over configurable time windows (e.g., 1 ms gate updated every 10 µs initially, then 2.5 µs).
Beam Abort Trigger: If the integrated dose in either moving sum exceeds a pre-set threshold, a beam-abort request is immediately generated and sent via fiber-optic cable to the SuperKEKB control system to dump the beams.
Long-Term Monitoring: The high-speed data is further summed (N2 = 10⁴) to create a 10 Hz data stream used for online and offline monitoring of integrated dose and correlation studies with accelerator variables.

6CCVD Solutions & Capabilities

The Belle II experiment demonstrates the critical need for high-quality, customized SCD materials in extreme radiation environments requiring ultra-fast response. 6CCVD is uniquely positioned to supply the next generation of diamond detectors for similar HEP, fusion, and high-power applications.

Applicable Materials

To replicate or extend the performance achieved at Belle II, researchers require the highest quality MPCVD diamond:

Optical Grade Single Crystal Diamond (SCD): Essential for radiation detection. Our SCD offers extremely low nitrogen content and high crystalline purity, maximizing Charge Collection Efficiency (CCE) and ensuring the long-term radiation hardness (10-20 Mrad tolerance) required for decades of operation.
Custom Thickness Control: We provide SCD layers from 0.1 µm up to 500 µm. Precise control over thickness is vital for optimizing detector capacitance and minimizing charge drift time, enabling the sub-2.5 µs response required by the 400 kHz abort logic.

Customization Potential

The Belle II system utilized 28 sensors in tight, specific locations (beam pipe, SVD structure, QCS bellows), necessitating custom geometries and robust electrical contacts.

Requirement from Belle II Paper	6CCVD Capability	Technical Specification
Small, Custom Dimensions	Precision Laser Cutting & Dicing	We provide custom plates/wafers up to 125mm, cut to the exact small sizes needed for tight space constraints around the beam pipe.
High-Quality Contacts	In-House Custom Metalization	We apply robust metal stacks (Au, Pt, Pd, Ti, W, Cu) optimized for ohmic contact stability under high bias voltage (O(100)V) and intense radiation flux.
Surface Finish	Ultra-Precision Polishing	SCD polishing to Ra < 1 nm ensures minimal surface defects, reducing leakage current and improving detector stability and signal-to-noise ratio.
Future Scaling	Large Area PCD Capability	For applications requiring larger area coverage (up to 125mm wafers) where single-crystal material is cost-prohibitive, our high-quality PCD offers excellent radiation hardness and uniformity.

Engineering Support

The successful operation of the Belle II system depends on optimizing material properties (purity, thickness) with complex electronics (400 kHz FPGA logic).

6CCVD’s in-house PhD team specializes in material science for extreme environments, offering expert consultation on material selection, doping levels, and geometry optimization for similar High Energy Physics (HEP) and Fast Timing projects.
We assist engineers in selecting the optimal diamond grade to ensure the necessary CCE and radiation tolerance for long-term, high-luminosity operation.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.5506/aphyspolb.51.1473