Time-of-flight methodologies with large-area diamond detectors for ion characterization in laser-driven experiments
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-10 |
| Journal | High Power Laser Science and Engineering |
| Authors | M. Salvadori, G. Di Giorgio, M. Cipriani, M. ScisciĂČ, C. Verona |
| Institutions | GSI Helmholtz Centre for Heavy Ion Research, National Agency for New Technologies, Energy and Sustainable Economic Development |
| Citations | 5 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the development and testing of an advanced, large-area polycrystalline diamond detector optimized for Time-of-Flight (TOF) ion diagnostics in extreme laser-driven plasma environments.
- Core Innovation: A large-area (15 mm x 15 mm) polycrystalline diamond sensor (150 ”m thick) is utilized to significantly increase the solid angle coverage and overall detection sensitivity.
- EMP Mitigation: The detector assembly features a tailored, multi-layer shielding design, including an internal Faraday cage and optimized grounding, achieving high rejection against severe Electromagnetic Pulses (EMPs).
- Performance Metrics: The detector demonstrated a fast temporal response (4.1 ns FWHM) and a Charge Collection Efficiency (CCE) of approximately 42% ± 21%.
- Sensitivity Gain: The large active area provides a sensitivity improvement ranging from 3.9 to 5.7 times compared to standard small-area single-crystal diamond detectors.
- Validation: The system was successfully tested at the PHELIX laser facility (IL ~ 1019 W/cm2), where EMP fields reached up to 100 kV/m.
- Experimental Results: The detector yielded high-quality proton spectra with a high signal-to-noise ratio (17.6 dB), characterizing protons up to 2.6 ± 0.3 MeV, proving its robustness in harsh environments.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sensor Material | Polycrystalline Diamond | II-a electronic grade | Ionizing radiation sensor |
| Sensor Dimensions | 15 x 15 | mm | Active area |
| Sensor Thickness | 150 | ”m | Charge collection depth |
| Electrode Stack Composition | 4 nm DLC / 4 nm Pt / 200 nm Au | nm | Sandwich electrode configuration |
| Bias Voltage (Typical) | +250 to +300 | V | Operation in velocity saturation regime |
| Temporal Response (FWHM) | 4.1 | ns | Measured using 5.486 MeV alpha particles |
| Charge Collection Efficiency (CCE) | 42 ± 21 | % | Polycrystalline diamond performance |
| Diamond Ionization Energy (e-h pair) | 13.1 | eV | eg value for spectrum reconstruction |
| Sensitivity Improvement Factor | 3.9 to 5.7 | times | Relative to standard single-crystal detectors |
| EMP Field Level (Test Environment) | Up to 100 | kV/m | Measured at PHELIX facility |
| Signal-to-Noise Ratio (SNR) | 17.6 | dB | Achieved during PHELIX shot |
| Inner Shielding Grid Mesh Step | 2 | mm | Designed for < 100 dB transmission up to 10 GHz |
| External Case Thickness | 2 | mm | Stainless steel walls (shielding down to ~500 Hz) |
| Proton Filter Thickness | 20 | ”m | Aluminum (Al) foil |
| Proton Cutoff Energy (20 ”m Al) | ~1.2 | MeV | Lower energy limit of detected spectrum |
Key Methodologies
Section titled âKey MethodologiesâThe characterization and deployment of the large-area diamond detector relied on a multi-step methodology combining offline calibration and advanced EMP mitigation techniques.
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Time-of-Flight (TOF) Measurement:
- The detector measures the arrival time (ti) of ions over a known distance (dTOF).
- The absolute interaction time (tbang) is referenced by the photopeak (tph) generated by prompt ionizing photons (UV-X).
- Ion energy (Ei) is calculated using the time difference (ti - tbang) and the classical relativistic relation (simplified for Ei < 10 MeV).
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Offline Detector Characterization:
- Temporal Response: Measured by exposing the detector to single 5.486 MeV alpha particles from a 241Am source, amplified by a 2 GHz fast amplifier (Cividec), yielding a 4.1 ns FWHM response.
- CCE Determination: A Pulse Height Spectrum (PHS) was generated using a charge-sensitive electronic chain (ORTEC 142A preamplifier, ORTEC 671 shaping amplifier). The peak shift from the ideal 100% bin determined the CCE (42% ± 21%).
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EMP Shielding Implementation:
- Internal Faraday Cage: The sensor is enclosed within an internal metallic shield, closed by a grounded copper grid (2 mm mesh step). This grid is designed to provide < 100 dB attenuation up to 10 GHz.
- External Housing: The assembly is mounted inside a 2 mm thick stainless steel cylindrical case, providing additional shielding, particularly effective for low-frequency electromagnetic waves (down to ~500 Hz).
- Cabling: Optimized grounding system and double-shielded cabling minimize coupling with transient EMP fields.
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Experimental Setup (PHELIX):
- The detector was placed 90 cm from the interaction point at 37 degrees from the target normal axis.
- A 20 ”m thick aluminum filter was used to block heavy ions and low-energy protons (< 1.2 MeV).
- EMP levels were independently monitored using a custom D-Dot differential electric-field probe (measuring up to 100 kV/m).
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Spectrum Reconstruction:
- The number of particles (Ni) is calculated from the integrated signal charge (Qc), corrected by the measured CCE and the ionization energy (eg).
- Energy loss correction due to the 20 ”m Al filter was applied using Monte Carlo SRIM calculations to accurately retrieve the incident proton spectrum.
Commercial Applications
Section titled âCommercial ApplicationsâThe robust design and high-performance characteristics of this large-area diamond detector make it suitable for advanced diagnostics in several high-energy and high-radiation fields:
- High Energy Density Physics (HEDP): Essential diagnostic tool for characterizing charged particle beams generated during high-intensity laser-matter interactions (I > 1019 W/cm2).
- Laser-Driven Acceleration Facilities: Deployment in next-generation high-power laser facilities (e.g., Apollon, L4 ATON) requiring reliable ion spectroscopy despite extreme EMP noise.
- Fusion Research: Used for real-time monitoring and characterization of accelerated ions (protons, heavy ions) in Inertial Confinement Fusion (ICF) experiments.
- Radiation Hardened Electronics: The EMP shielding methodology and detector housing design are directly applicable to protecting sensitive electronics used near pulsed power or high-current discharge systems.
- Nuclear and Particle Physics: Applications requiring large solid angle coverage and high temporal resolution for low-flux charged particle detection.
View Original Abstract
Abstract The time-of-flight technique coupled with semiconductor detectors is a powerful instrument to provide real-time characterization of ions accelerated because of laser-matter interactions. Nevertheless, the presence of strong electromagnetic pulses (EMPs) generated during the interactions can severely hinder its employment. For this reason, the diagnostic system must be designed to have high EMP shielding. Here we present a new advanced prototype of detector, developed at ENEA-Centro Ricerche Frascati (Italy), with a large-area (15 mm Ă 15 mm) polycrystalline diamond sensor having 150 ÎŒm thickness. The tailored detector design and testing ensure high sensitivity and, thanks to the fast temporal response, high-energy resolution of the reconstructed ion spectrum. The detector was offline calibrated and then successfully tested during an experimental campaign carried out at the PHELIX laser facility ( ${E}_L\sim$ 100 J, ${\tau}_L = 750$ fs, ${I}_L\sim \left(1{-}2.5\right)\times {10}^{19}$ W/cm 2 ) at GSI (Germany). The high rejection to EMP fields was demonstrated and suitable calibrated spectra of the accelerated protons were obtained.