Proton Recoil Telescope Based on Diamond Detectors for the Measurement of Fusion Neutrons
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-05-24 |
| Journal | IEEE Transactions on Nuclear Science |
| Authors | B. Caiffi, M. Osipenko, M. Ripani, M. Pillon, M. Taiuti |
| Institutions | National Agency for New Technologies, Energy and Sustainable Economic Development, Istituto Nazionale di Fisica Nucleare |
| Citations | 6 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Fusion Neutron Diagnostics
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Fusion Neutron DiagnosticsâExecutive Summary
Section titled âExecutive SummaryâThis research validates the use of segmented MPCVD diamond detectors in a Proton Recoil Telescope (PRT) configuration for high-resolution 14 MeV fusion neutron diagnostics, specifically addressing the harsh environment requirements of reactors like ITER.
- Core Value Proposition: CVD diamond offers superior radiation hardness (43 eV displacement energy), high speed (2000 ”m2/(Vs) mobility), and low intrinsic noise due to its 5.5 eV bandgap, making it ideal for high-flux, high-temperature fusion environments.
- Methodology: The PRT uses two aligned SCD crystals in coincidence, placed behind a plastic converter, to measure the energy of recoiled protons and effectively reject the large background from elastic neutron scattering on 12C nuclei.
- Key Challenge Addressed: The ideal configuration (Prototype 1) requires ultra-thin SCD crystals (30 ”m) to achieve the lowest energy threshold (2 MeV spectrum reconstruction), a thickness currently difficult to source commercially.
- 6CCVD Competitive Advantage: 6CCVD specializes in custom SCD fabrication, offering thicknesses down to 0.1 ”m, directly enabling the realization of the ideal Prototype 1 configuration necessary for optimal performance.
- Performance Metrics: The tested prototype demonstrated an efficiency of 2.5 x 10-6 for 14 MeV neutrons and an energy resolution of 70 keV (fast chain readout).
- Application: Critical technology for neutron spectrometry and monitoring structural damage/activation in next-generation fusion reactors (e.g., ITER).
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the critical material and performance parameters extracted from the study of the diamond-based proton recoil telescope prototypes.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Neutron Energy | 14 | MeV | D-T Fusion Reaction |
| Required Operating Temp | High | °C | Diamond operates without cooling (5.5 eV bandgap) |
| Charge Carrier Mobility | 2000 | ”m2/(Vs) | Ensures fast charge collection (< few ns) |
| Diamond Band Gap | 5.5 | eV | Suppresses dark current noise |
| Displacement Energy | 43 | eV | Highest radiation hardness among neutron detectors |
| Ideal D1 Thickness (Prot. 1) | 30 | ”m | Required for E > 2 MeV spectrum reconstruction |
| Ideal D2 Thickness (Prot. 1) | 700 | ”m | Required to stop 14 MeV recoiled protons |
| Commercial D1 Thickness (Prot. 2) | 300 | ”m | Limits reconstruction threshold to E > 8 MeV |
| Crystal Area (Simulated) | 3 x 3 | mm2 | Sensitive volume dimensions |
| Converter Material | Polyethylene (C2H4) | N/A | Induces (n,p) reaction |
| Converter Thickness | 20 | ”m | Optimized for conversion efficiency |
| Contact Thickness (Simulated) | 50 | nm | Cr contacts |
| Measured Efficiency (14 MeV) | 2.5 x 10-6 | N/A | Tested prototype (500/500 ”m crystals) |
| Energy Resolution (Fast Chain) | 70 | keV | Limited by 11° solid angle aperture |
Key Methodologies
Section titled âKey MethodologiesâThe experimental approach focused on optimizing the geometry and material thicknesses of the segmented CVD diamond detector to maximize efficiency and background rejection for 14 MeV neutron spectrometry.
- Detector Configuration: The system was arranged as a Proton Recoil Telescope (PRT), consisting of a plastic (polyethylene) converter placed immediately in front of two sequential CVD diamond crystals (D1 and D2).
- Signal Generation: Incoming neutrons interact with the converter via the (n,p) reaction, generating recoiled protons. These protons pass through D1 (measuring dE/dx) and stop in D2 (measuring Etotal).
- Background Rejection: Fast coincidence measurements between D1 and D2 signals were used to reject background events, primarily those caused by elastic scattering of neutrons on the 12C atoms within the diamond crystals.
- Thickness Optimization (Simulation): Monte Carlo simulations (Geant4) were performed on three prototypes with varying SCD thicknesses (30/700 ”m, 300/500 ”m, 100/600 ”m) to determine the optimal configuration for achieving the lowest energy reconstruction threshold (down to 2 MeV).
- Prototype Assembly: A preliminary prototype was assembled using standard, commercially available electronic grade Single Crystal Diamond (SCD) detectors (500 ”m thick, 4.7 x 4.7 mm2 area) aligned 1.2 cm apart.
- Experimental Validation: Testing was conducted at the Frascati Neutron Generator (FNG) using 14 MeV neutrons generated by T(d,n)α fusion reactions, utilizing both charge sensitive (250 keV resolution) and fast (70 keV resolution) electronic readout chains.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights a critical need for highly customized, ultra-thin Single Crystal Diamond (SCD) materials to achieve optimal performance in fusion neutron diagnostics. 6CCVD is uniquely positioned to supply the necessary materials and fabrication services required to replicate and extend this research, particularly the ideal Prototype 1 configuration.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the low energy threshold (E > 2 MeV) and high resolution demonstrated in the simulations, the following 6CCVD materials are required:
| Material Specification | Requirement from Paper | 6CCVD Capability | Advantage |
|---|---|---|---|
| Single Crystal Diamond (SCD) | Electronic Grade, High Purity | High-quality SCD wafers | Superior charge collection and intrinsic noise suppression. |
| Custom Thickness (D1) | 30 ”m (Ideal Prototype 1) | SCD available from 0.1 ”m to 500 ”m | Directly enables the ideal 30 ”m first crystal, which is currently unavailable commercially, allowing E > 2 MeV spectrum reconstruction. |
| Custom Thickness (D2) | 700 ”m | Substrates available up to 10 mm | Easily meets the 700 ”m thickness requirement for stopping high-energy protons. |
| Polycrystalline Diamond (PCD) | N/A (SCD preferred) | Wafers up to 125 mm | Available for large-area, lower-cost applications if SCD is not strictly required. |
Customization Potential
Section titled âCustomization PotentialâThe success of the PRT design relies heavily on precise dimensions, specific thicknesses, and reliable electrical contacts. 6CCVD offers comprehensive customization services to meet these exact engineering requirements:
- Precision Thickness Control: We can grow and polish SCD wafers to the exact optimized thicknesses (e.g., 30 ”m ± 5 ”m) required for the first detector (D1) to minimize the detection threshold.
- Custom Dimensions and Segmentation: The paper utilized small 3 x 3 mm2 crystals. 6CCVD provides custom laser cutting and dicing to produce segmented detectors of any required size and geometry up to 125 mm wafers.
- Advanced Metalization Services: The simulated prototypes used 50 nm Cr contacts. 6CCVD offers in-house metalization capabilities, including:
- Standard Contacts: Au, Pt, Pd, Ti, W, Cu.
- Custom Stacks: Fabrication of specific metal stacks (e.g., Ti/Pt/Au or custom Cr-based contacts) optimized for ohmic performance and harsh environment stability.
- Surface Finish: SCD detectors require ultra-smooth surfaces for reliable thin-film contacts. 6CCVD guarantees Ra < 1 nm polishing for SCD, ensuring optimal electronic performance and bonding.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science and application engineering of CVD diamond. We provide expert consultation for projects requiring high-performance detectors in extreme environments.
- Material Selection for Fusion Diagnostics: We assist researchers in selecting the optimal SCD grade (electronic vs. optical) and thickness profile necessary for similar fusion neutron spectrometry projects, ensuring the best balance between energy resolution, efficiency, and cost.
- Design Optimization: We offer support in optimizing crystal geometry and metal contact design to minimize non-sensitive volumes and electronic noise, crucial for maximizing the signal-to-noise ratio in high-flux environments.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Diamonds are very promising candidates for the neutron diagnostics in harsh environments such as fusion reactors because of their proven radiation hardness. In comparison to the standard neutron diagnostics currently used (i.e., fission chambers, silicon based detectors, scintillators) CVD diamonds are less sensitive to $\gamma $ rays, which represents a huge background in fusion devices. Furthermore, their low leakage current provides a high energy resolution. A CVD diamond based detector has been proposed for the measurement of the 14 MeV neutrons from DT fusion reaction. The prototype was arranged in a proton recoil telescope configuration, featuring a plastic converter in front of the sensitive volume, in order to induce the (n, n) reactions which generate the recoil protons. The segmentation of the sensitive volume, achieved using two crystals with two dedicated electronic readouts, allowed to perform measurements in coincidence, which suppressed the neutron-carbon elastic scattering background. A preliminary prototype was assembled and tested at FNG (Frascati Neutron Generator), showing promising results regarding efficiency and energy resolution. © 2016 IEEE.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2003 - Geant4