Precision Electron-Beam Polarimetry at 1 GeV Using Diamond Microstrip Detectors
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2016-02-16 |
| Journal | Physical Review X |
| Authors | A. Narayan, D Jones, J. C. Cornejo, M. M. Dalton, W. Deconinck |
| Institutions | Mississippi State University, Thomas Jefferson National Accelerator Facility |
| Citations | 25 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: High-Precision Polarimetry using MPCVD Diamond Detectors
Section titled “Technical Documentation & Analysis: High-Precision Polarimetry using MPCVD Diamond Detectors”Executive Summary
Section titled “Executive Summary”This research demonstrates the successful deployment of CVD diamond microstrip detectors for high-precision particle tracking in a high-radiation environment, setting a new benchmark for electron-beam polarimetry.
- Record Precision: Achieved the highest precision measurement of 1.16 GeV electron beam polarization to date, with a systematic uncertainty of 0.59%.
- Novel Application: This marks the first successful use of diamond microstrip detectors as particle tracking detectors in a physics experiment, demonstrating stable operation over two years.
- Material Validation: Synthetic CVD diamond proved superior due to its inherent radiation hardness, low noise characteristics (~1000 e-), and insensitivity to synchrotron radiation.
- Detector Design: The detectors utilized high-granularity microstrips (200 µm pitch) and a custom Ti-Pt-Au metalization scheme to capture the full Compton electron spectrum.
- Future Viability: The results confirm that diamond-based tracking is the superior choice for meeting the extremely stringent polarimetry goals (< 0.4% uncertainty) required by future Standard Model tests like SOLID and MOLLER.
- 6CCVD Advantage: 6CCVD specializes in providing the custom dimensions, high-purity SCD/PCD material, and advanced metalization (Ti/Pt/Au) necessary to replicate and exceed the performance achieved in this study.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the research paper, detailing the operational parameters and detector characteristics.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electron Beam Energy | 1.16 | GeV | Continuous Wave (CW) |
| Beam Current | 180 | µA | Operating condition |
| Systematic Uncertainty (Achieved) | 0.59 | % | Total measurement precision |
| Polarization Uncertainty (Future Goal) | < 0.4 | % | Required for SOLID/MOLLER |
| Diamond Plate Dimensions | 21 x 21 x 0.5 | mm3 | CVD Synthetic Diamond |
| Electrode Strips | 96 | - | Horizontal, single side |
| Strip Pitch | 200 | µm | Center-to-center spacing |
| Metalization Stack | Ti-Pt-Au | - | Novel electrode material |
| HV Bias | ~ -300 | V | Applied to back side |
| Detector Signal (MIP) | ~ 9000 | e- | Charge generated |
| Detector Noise | ~ 1000 | e- | Typical channel noise |
| Trigger Rate (Typical) | 70 - 90 | kHz | Track-finding algorithm |
Key Methodologies
Section titled “Key Methodologies”The successful implementation relied on advanced material selection, precise fabrication, and robust electronic integration.
- Material Selection: Synthetic diamond plates (21 x 21 x 0.5 mm3) grown via Chemical Vapor Deposition (CVD) were chosen specifically for their well-established radiation hardness [21, 22] and insensitivity to synchrotron radiation.
- Electrode Fabrication: A novel Ti-Pt-Au metalization scheme was employed to deposit 96 horizontal electrode strips onto the diamond surface.
- High Granularity Patterning: The strips were patterned with a 200 µm pitch (180 µm metal width and a 20 µm gap) to ensure the high spatial resolution required to measure the shape of the Compton spectrum.
- Detector Assembly: The diamond plates were mounted onto alumina carrier boards using silver epoxy, and aluminum wire bonds connected the strips to Au traces.
- Bias Application: A high voltage bias of approximately -300 V was applied to the back side of the diamond plate.
- Tracking System: Four planes of these diamond microstrip detectors were deployed in a magnetic chicane to track Compton scattered electrons, positioned as close as 5 mm from the primary beam.
- Noise Suppression: An FPGA-based track-finding algorithm was implemented in the Data Acquisition (DAQ) system, suppressing electronic noise by a factor of 100-200 compared to untriggered mode.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the high-purity MPCVD diamond materials and custom fabrication services required to replicate this high-precision polarimetry experiment and meet the even stricter requirements of future projects like SOLID and MOLLER (< 0.4% uncertainty).
Applicable Materials
Section titled “Applicable Materials”The paper utilized CVD diamond for its radiation hardness. To achieve the next generation of precision, 6CCVD recommends the following materials, optimized for charge collection and large area coverage:
| 6CCVD Material | Recommended Grade | Application Benefit |
|---|---|---|
| Single Crystal Diamond (SCD) | Electronic Grade (High Purity) | Superior charge collection efficiency, highest carrier mobility, and lowest intrinsic noise for optimal signal-to-background ratio (critical for < 0.4% precision). Thicknesses available from 0.1 µm to 500 µm. |
| Polycrystalline Diamond (PCD) | Optical/Electronic Grade | Cost-effective solution for large-area tracking planes. 6CCVD offers PCD plates up to 125 mm in diameter, significantly exceeding the 21 mm dimensions used in the paper. |
| Boron-Doped Diamond (BDD) | Heavy Doping | Potential use as highly stable, radiation-hard reference electrodes or sensors in extreme environments where conductivity is required. |
Customization Potential
Section titled “Customization Potential”The detector design relies heavily on precise dimensions and custom metalization, both core competencies of 6CCVD.
| Requirement from Paper | 6CCVD Capability | Specification Match |
|---|---|---|
| Custom Dimensions | Plates/Wafers up to 125 mm (PCD) or custom SCD sizes. | We can supply the exact 21 x 21 x 0.5 mm3 plates or larger formats for increased acceptance. |
| Thickness Control | SCD and PCD thickness control from 0.1 µm to 500 µm. | Precise control over the required 500 µm thickness, ensuring uniformity across multiple detector planes. |
| Metalization Stack | Internal capability for custom metal stacks. | We offer the exact Ti/Pt/Au metalization used for the microstrips, ensuring compatibility with established readout electronics and bonding techniques (Al wire bonds). We also offer Au, Pt, Pd, W, and Cu. |
| High Granularity | Advanced photolithography and laser cutting services. | We can pattern the required 200 µm pitch microstrips and provide custom laser cutting for complex geometries or apertures needed for beamline integration. |
| Surface Finish | Polishing to Ra < 1 nm (SCD) or Ra < 5 nm (PCD). | High-quality polishing ensures optimal surface preparation for reliable metal adhesion and low leakage current. |
Engineering Support
Section titled “Engineering Support”The successful implementation of diamond tracking detectors requires deep expertise in material science, surface physics, and high-energy physics integration.
- Expert Consultation: 6CCVD’s in-house PhD team specializes in MPCVD growth and detector physics. We offer comprehensive engineering support for projects requiring high-radiation particle tracking and high-precision polarimetry.
- Design Optimization: We assist researchers in selecting the optimal diamond grade (SCD vs. PCD) and thickness to maximize charge collection efficiency (CCE) and minimize noise, crucial for achieving the < 0.4% uncertainty goal.
- Global Logistics: We provide reliable global shipping (DDU default, DDP available) to ensure timely delivery of critical components to international research facilities like Jefferson Lab.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We report on the highest precision yet achieved in the measurement of the polarization of a low-energy, O(1 GeV), continuous-wave (CW) electron beam, accomplished using a new polarimeter based on electron-photon scattering, in Hall C at Jefferson Lab. A number of technical innovations were necessary, including a novel method for precise control of the laser polarization in a cavity and a novel diamond microstrip detector that was able to capture most of the spectrum of scattered electrons. The data analysis technique exploited track finding, the high granularity of the detector, and its large acceptance. The polarization of the 180-mu A, 1.16-GeV electron beam was measured with a statistical precision of < 1% per hour and a systematic uncertainty of 0.59%. This exceeds the level of precision required by the Qweak experiment, a measurement of the weak vector charge of the proton. Proposed future low-energy experiments require polarization uncertainty < 0.4%, and this result represents an important demonstration of that possibility. This measurement is the first use of diamond detectors for particle tracking in an experiment. It demonstrates the stable operation of a diamond-based tracking detector in a high radiation environment, for two years.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
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