Performance and perspectives of the diamond based Beam Condition Monitor for beam loss monitoring at CMS
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-07-03 |
| Journal | Proceedings of Technology and Instrumentation in Particle Physics 2014 â PoS(TIPP2014) |
| Authors | M. Guthoff, W. De Boer, Anne Dabrowski, F. Kassel, David Stickland |
| Institutions | Karlsruhe Institute of Technology, European Organization for Nuclear Research |
| Analysis | Full AI Review Included |
Technical Analysis of Diamond Beam Condition Monitors for High Energy Physics
Section titled âTechnical Analysis of Diamond Beam Condition Monitors for High Energy PhysicsâExecutive Summary
Section titled âExecutive SummaryâThis document analyzes the performance requirements and operational challenges of CVD diamond sensors utilized in the CMS Beam Condition Monitor (BCM) at the Large Hadron Collider (LHC), focusing on implications for material scientists and engineers requiring radiation-hard solutions.
- Application: Diamond sensors (poly-crystalline CVD) serve as crucial high-rate beam loss monitors protecting sensitive silicon trackers at CMS.
- Core Material: Both poly-crystalline CVD (pCVD) and single-crystalline CVD (sCVD) diamond were tested, chosen specifically for their intrinsic radiation hardness.
- Critical Operational Issue: A severe polarization effect was observed, leading to a signal efficiency decrease up to 50 times greater than initial expectations during LHC Run 1 (2010-2013).
- Mechanism of Failure: This signal degradation is attributed to charge carriers (primarily trapped holes) accumulating at radiation-induced lattice defects, deforming the internal electric field.
- Diagnostic Technique: The Transient-Current-Technique (TCT) was used, employing 241Am (alpha source) to probe the electric field while 90Sr (beta source) simulated the bulk radiation (pumping) environment.
- Conclusion: The findings underscore the need for ultra-high purity CVD diamond materials (SCD) with minimum lattice defect density to mitigate space charge buildup in high-fluence environments.
- 6CCVD Value Proposition: 6CCVD supplies tailored, ultra-high purity SCD and inch-size PCD optimized for extreme radiation tolerance and precision detector fabrication.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material Types | CVD Diamond | - | Poly-crystalline (pCVD) and Single-crystalline (sCVD) |
| Sensor Area | 1 x 1 | cm2 | Standard dimensions for BCM2/1L |
| pCVD Thickness (Operational) | ~400 | ”m | Typical operational sensor depth |
| sCVD Thickness (TCT Sample) | 460 | ”m | Sample used for post-irradiation analysis |
| Bias Voltage (Operational) | 200 | V | Applied HV during LHC operation |
| Average Internal E-Field | 0.43 - 0.5 | V/”m | Calculated based on applied voltage and thickness |
| Measured Signal Decrease | Up to 50 | times stronger | Efficiency loss compared to initial prediction |
| Cumulative Fluence (sCVD tested) | 5.7 x 1014 | cm-2 | 24 GeV proton equivalent |
| TCT Pumping Source | 3.56 | MBq | 90Sr (simulates high-rate bulk charge deposition) |
| TCT Probing Source | 3.56 | kBq | 241Am (used for electron/hole drift observation) |
| Measurement Bandwidth | 1 | GHz | System limit set by signal amplifier |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized operational monitoring data from the LHC Run 1 and specific post-irradiation Transient-Current-Technique (TCT) measurements to diagnose field deformation in the sensors:
- In-Situ Monitoring: Operational CVD diamond sensors in CMS (BCM2/1L) monitored signal output relative to instantaneous luminosity over LHC Run 1 (2010-2013), quantifying the loss of efficiency.
- Radiation Pumping: A highly irradiated sCVD sample (460 ”m thick, 5.7 x 1014 cm-2 fluence) was exposed to a 90Sr beta source (3.56 MBq) to continuously pump charge into the bulk material, simulating the high-rate environment.
- Field Probing (TCT): A weak 241Am alpha source (3.56 kBq) was used to inject electron-hole pairs precisely at the cathode or anode. The resulting current pulse, driven by charge carrier drift, reveals the internal electric field distribution.
- Polarization Analysis: Measurements were taken immediately after HV switch-on (unpolarized, square TCT pulse) and again after approximately 40 minutes of pumping, demonstrating the deformation of the pulse shape due to space charge buildup.
- Simulation & Validation: A 1-D simulation of charge carrier drift, trapping, and de-trapping was performed. This confirmed that the observed electric field deformation and TCT pulse shapes resulted from hole trapping being the dominant mechanism over electron trapping.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights that while diamond is inherently radiation-hard, minimizing lattice defects and maximizing material purity is paramount for sustained high-rate detector operation. 6CCVDâs specialized MPCVD diamond capabilities are directly engineered to address these challenges for particle physics applications.
| Applicable Materials & Material Requirements | 6CCVD Solution & Capability | Engineering Benefit |
|---|---|---|
| Requirement: Mitigation of Polarization Effect (Low Defect Density) | Optical Grade Single Crystal Diamond (SCD): Guaranteed ultra-high purity (N < 5 ppb). | Minimizes native lattice defects that serve as charge trapping centers, preventing internal E-field deformation and ensuring stable signal efficiency over high integrated fluence. |
| Requirement: Large Area Detector Construction (1 x 1 cm2) | High Quality Polycrystalline Diamond (PCD) Wafers: Custom dimensions up to 125 mm diameter. | Enables scale-up of detector arrays for future collider generations (e.g., HL-LHC) requiring larger coverage or simplified assembly. |
| Requirement: Precision Thickness Control (400 - 460 ”m range) | SCD/PCD Thickness Control: Capabilities from 0.1 ”m up to 500 ”m (wafers) and substrates up to 10 mm. | Allows researchers to tune detector depth precisely for optimal charge collection efficiency and minimized parasitic capacitance. |
| Requirement: High-Quality Electrical Contacts (for 200V operation) | Custom Metalization Services: Internal deposition capabilities including Au, Pt, Pd, Ti, W, and Cu. | Provides robust, low-resistivity ohmic contacts necessary for stable high-voltage operation in high-vacuum and radiation environments. |
| Requirement: Uniformity for TCT/High E-Field | Precision Polishing (Ra < 1 nm for SCD): Industry-leading surface finishes. | Ensures minimal surface leakage, uniform charge injection, and reduced surface scattering, critical for both TCT diagnostics and long-term detector stability. |
| Logistics & Support | Global Shipping & Expert Consultation: DDU default, DDP available worldwide. In-house PhD engineering team support. | Seamless integration of custom materials into global research supply chains and direct access to specialized expertise for designing next-generation diamond detectors. |
6CCVDâs in-house PhD team provides specialized engineering support for projects requiring extreme radiation hardness, specific charge carrier mobility requirements, or custom TCT measurement geometries. We are uniquely positioned to assist researchers in selecting materials that overcome the polarization limitations highlighted by this study.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
At CMS, a beam loss monitoring system is operated to protect the silicon detectors from high particle rates, arising from intense beam loss events. As detectors, poly-crystalline CVD diamond sensors are placed around the beam pipe at several locations inside CMS. In case of extremely high detector currents, the LHC beams are automatically extracted from the LHC rings.Diamond is the detector material of choice due to its radiation hardness. Predictions of the detector lifetime were made based on FLUKA monte-carlo simulations and irradiation test results from the RD42 collaboration, which attested no significant radiation damage over several years.During the LHC operational Run1 (2010 Ăą?? 2013), the detector efficiencies were monitored. A signal decrease of about 50 times stronger than expectations was observed in the in-situ radiation environment. Electric field deformations due to charge carriers, trapped in radiation induced lattice defects, are responsible for this signal decrease. This so-called polarization effect is rate dependent and results in a non-linearity of the detector response. Measurements using the transient current technique reveal the electric field distribution. Online measurements and laboratory analysis of polarization effects in diamond sensors are presented.In the scope of the HL-LHC upgrade, various changes are foreseen. Perspectives for upgrades of the detector electronics are presented. Different candidates for sensor technologies are tested for their performance in a high rate, highly damaging radiation environment.