Time-of-flight methodologies with large-area diamond detectors for ion characterization in laser-driven experiments

At a Glance

Metadata	Details
Publication Date	2022-01-10
Journal	High Power Laser Science and Engineering
Authors	M. Salvadori, G. Di Giorgio, M. Cipriani, M. Scisciò, C. Verona
Institutions	National Agency for New Technologies, Energy and Sustainable Economic Development, University of Pisa
Citations	5
Analysis	Full AI Review Included

Diamond Detectors for Extreme Environments: Technical Analysis and 6CCVD Solutions

Executive Summary

This research paper details the development and successful testing of a novel large-area polycrystalline diamond (PCD) detector optimized for Time-of-Flight (TOF) ion characterization in high-energy laser-driven experiments, where strong electromagnetic pulses (EMPs) typically hinder diagnostics.

The core value proposition and key achievements of the advanced detector are summarized below:

Expanded Detection Area: Utilizes a large 15 mm x 15 mm Polycrystalline Diamond (PCD) sensor, increasing the detection solid angle by approximately one order of magnitude compared to traditional 5 mm x 5 mm Single Crystal Diamond (SCD) detectors.
Sensitivity Enhancement: Achieved a substantial overall sensitivity improvement ranging from 3.9x to 5.7x over conventional SCD systems, critical for characterizing low fluxes of emitted particles.
Robust EMP Rejection: The custom-designed, multi-layered shielding assembly (Faraday cage, double grids, 2 mm stainless steel case) proved highly effective, successfully acquiring high signal-to-noise ratio data (17.6 dB) in environments generating extreme EMP fields (up to 100 kV/m).
Fast Response Time: The 150 µm PCD wafer demonstrated a fast temporal response with a Full Width at Half Maximum (FWHM) of 4.1 ns, crucial for high-resolution ion spectrum reconstruction.
High-Intensity Validation: The system was successfully validated at the PHELIX laser facility, characterizing proton spectra generated by laser intensities up to (1-2.5) x 10¹⁹ W/cm².
Material Specifications: Sensor constructed from 150 µm thick, II-a electronic grade PCD, metalized with layers of DLC (4 nm), Platinum (4 nm), and Gold (200 nm).

Technical Specifications

The following table summarizes the hard data and performance metrics extracted from the research paper.

Parameter	Value	Unit	Context
Detector Material	Polycrystalline Diamond (PCD)	N/A	High-quality, II-a electronic grade.
Wafer Dimensions	15 x 15	mm	Large area, improving solid angle coverage.
Wafer Thickness	150	µm	Standard thickness for fast charge collection.
Temporal Resolution (FWHM)	4.1	ns	Determined by single particle detection (5.486 MeV α).
Charge Collection Efficiency (CCE)	42% ± 21%	%	Polycrystalline material, lower than SCD (68%-98%).
Sensitivity Improvement	3.9x to 5.7x	N/A	Improvement ratio (PCD vs. 5x5 mm SCD) based on Area * CCE.
Maximum Measured Proton Energy	2.6 ± 0.3	MeV	Obtained during PHELIX experimental shot.
EMP Field Rejection	17.6	dB	Signal-to-Noise Ratio (SNR) achieved in high-EMP environment.
External EMP Field Level	Up to 100	kV/m	Measured at 120 cm from the interaction point.
Laser Intensity (Main Pulse)	(1-2.5) x 10¹⁹	W/cm²	Extreme environment test at PHELIX.
Detector Bias Voltage (Test Shot)	+300	V	Applied across the 150 µm PCD wafer.
Filter Thickness/Material	20	µm	Aluminum (Al) filter used to cut off heavy ions (< 1.2 MeV protons).

Key Methodologies

The detector was characterized and tested using a robust multi-step approach focused on maximizing sensitivity while minimizing EMP interference.

Material Selection and Fabrication:
- Utilized a commercial, 150 µm thick, II-a electronic grade PCD structure (15 mm x 15 mm) for optimal temporal response and high sensitivity across a large area.
- Wafers were enclosed between metallic electrodes consisting of 4 nm Diamond-Like Carbon (DLC), 4 nm Platinum (Pt), and 200 nm Gold (Au) layers, providing a constant electric field for charge collection.
Performance Calibration (Offline):
- Temporal response (FWHM) and CCE were measured by exposing the detector to monochromatic alpha (α) particles (E_α = 5.486 MeV) emitted by a ²⁴¹Am radioactive source.
- CCE was quantified via Pulse Height Spectrum (PHS) analysis, yielding a characteristic 42% ± 21% CCE for the polycrystalline structure.
EMP Shielding Design:
- An advanced, multi-stage EMP rejection housing was engineered, consisting of an internal double Faraday cage system.
- Grids: Two copper grids were used: a biased grid (4.5 mm mesh step, up to 5 kV bias) and a grounded grid (2 mm mesh step, integral to the internal metallic shield).
- Housing: The assembly was placed in an external cylindrical case made of 2 mm thick stainless steel, providing shielding down to 500 Hz via the electromagnetic skin effect.
Experimental Setup (PHELIX Validation):
- The detector was biased at +300 V and positioned 90 cm from the interaction point, 37° from the target normal axis.
- A 20 µm Al filter was placed in front of the diamond to cut off heavy ion contributions (protons < 1.2 MeV cutoff).
- Laser System: Used a combination of a nanosecond prepulse (5 x 10¹³ W/cm²) followed 3 ns later by a high-intensity 750 fs main pulse ((1-2.5) x 10¹⁹ W/cm²) on a foam target.
- EMP Monitoring: EMP fields were independently monitored via a custom D-Dot differential electric-field probe (measuring up to 100 kV/m fields).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the MPCVD diamond required to replicate, extend, and optimize the ion diagnostics research detailed in this paper. Our specialization in advanced large-area and custom diamond engineering directly addresses the challenges of sensitivity and EMP resilience.

Applicable Materials

The successful implementation relies on high-quality MPCVD material, which 6CCVD provides with precise control over growth and doping parameters.

Application Requirement	6CCVD Material Recommendation	Rationale and Optimization
Large-Area Sensitivity	High-Quality Polycrystalline Diamond (PCD)	We provide MPCVD PCD wafers up to 125 mm diameter, allowing for even larger detection angles and solid-angle coverage than the 15x15 mm used, maximizing sensitivity for low-flux experiments (e.g., p-¹¹B fusion).
High Temporal Resolution	High-Purity Single Crystal Diamond (SCD)	For experiments where peak energy resolution is paramount, 6CCVD supplies SCD (up to 98% CCE). While current SCD sizes are smaller, using multiple SCD sensors or optimizing crystal orientation can achieve superior time resolution (< 0.5 ns FWHM).
Harsh Environment Robustness	Intrinsic MPCVD Diamond (PCD/SCD)	Diamond’s wide bandgap (5.5 eV) ensures intrinsic radiation hardness and high tolerance to high bias voltages and intense laser-plasma environments, essential for reliable operation during high-rate EMP exposure.

Customization Potential

The research highlights the necessity of tailored materials and custom detector geometries for optimal performance in large-scale laser facilities. 6CCVD offers the following engineering services:

Custom Dimensions and Thicknesses: We can replicate the exact 150 µm thickness and large-area geometry (15 mm x 15 mm) in PCD, or produce custom sizes up to our 125 mm diameter limit. We offer substrates up to 10 mm thick for specialized mechanical or thermal applications.
Metalization Expertise: The detector used a complex DLC/Pt/Au electrode stack. 6CCVD offers extensive in-house metalization services, including Ti/Pt/Au, W, Cu, and Pd, enabling precise contact engineering and optimization of charge collection efficiency (CCE) for specific bias regimes.
Precision Fabrication: For integrating the diamond wafer into advanced mechanical assemblies like the multi-grid EMP shielding system described, 6CCVD provides precision laser cutting and patterning services to achieve highly accurate edge alignment and electrode positioning.
Surface Preparation: We guarantee polishing standards of R_a < 5 nm for inch-size PCD wafers, ensuring consistent surface quality critical for reliable electrical contact and signal integrity.

Engineering Support & Global Logistics

Expert Consultation: 6CCVD’s in-house PhD material science and engineering team can assist clients in selecting the optimal diamond material (PCD vs. SCD, thickness, doping level) to maximize the CCE and temporal response for similar Time-of-Flight (TOF) Ion Diagnostics or Laser-Matter Interaction projects.
Global Supply Chain: We ensure reliable global delivery (DDU default, DDP available) for sensitive research components, minimizing lead times for experimental campaigns.

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

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 × 15 mm) polycrystalline diamond sensor having 150 μm 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.

Tech Support

Original Source

DOI: https://doi.org/10.1017/hpl.2021.59