Accurate spectra for high energy ions by advanced time-of-flight diamond-detector schemes in experiments with high energy and intensity lasers

At a Glance

Metadata	Details
Publication Date	2021-02-04
Journal	Scientific Reports
Authors	M. Salvadori, F. Consoli, C. Verona, M. Cipriani, M.P. Anania
Institutions	National Agency for New Technologies, Energy and Sustainable Economic Development, University of Lisbon
Citations	26
Analysis	Full AI Review Included

Technical Documentation & Analysis: Advanced CVD Diamond TOF Detectors

Source Paper: Accurate spectra for high energy ions by advanced time-of-flight diamond-detector schemes in experiments with high energy and intensity lasers (Scientific Reports, 2021)

Executive Summary

This research validates an advanced Time-of-Flight (TOF) diagnostic methodology utilizing Chemical Vapor Deposition (CVD) diamond detectors, specifically optimized for the extreme environment of high-intensity laser-plasma interaction experiments.

EMP Resilience: Successfully mitigates severe Electro Magnetic Pulses (EMPs) (estimated at ~25 kV/m peak-to-peak) through tailored detector mounting, waveguide transmission lines, and shielded coaxial cables, achieving high signal-to-noise ratio (SNR).
High Resolution: Confirms the necessity of thin SCD layers (50 µm) to achieve fast time response (Δt = 0.8 ns), crucial for high-resolution energy spectrum reconstruction of accelerated protons.
Scalable Architecture: Proposes and validates the core module for a novel stacked diamond detector structure, enabling simultaneous high sensitivity (via cumulative thickness) and high energy resolution (via thin layers).
Performance: Achieved accurate, calibrated proton spectra up to ~2.5 MeV in a 100 TW, 2 x 10¹⁹ W/cm² TNSA regime experiment.
Advanced Techniques: Implements sophisticated signal processing, including a calibrated splitter for high dynamic range (~74 dB) and a cable de-embedding procedure using S₂₁ scattering parameters to maintain signal integrity.
Future Applications: Confirms CVD diamond’s role as the ideal, radiation-hard, high-repetition rate diagnostic for next-generation high-energy facilities (e.g., ELI, PETAL).

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Laser Peak Power	100	TW	FLAME Ti:Sapphire laser facility
Maximum Laser Intensity (I_L)	2 x 10¹⁹	W/cm²	On 10 µm Al target
Diamond Active Layer Thickness	50	µm	Intrinsic CVD Diamond
Diamond Substrate Material/Thickness	HPHT	0.5 mm	Used as mechanical support
Detector Dimensions	4 x 4	mm	Planar interdigital configuration
Interdigital Contact Geometry	20 / 20	µm	Width / Spacing (Aluminum)
Achieved Time Resolution (Δt)	0.8	ns	For 5.486 MeV α particles
3-dB Frequency Bandwidth (f_3dB)	625	MHz	Detector response
Maximum Proton Energy Detected	~2.5	MeV	Calibrated spectrum accuracy
TOF Distance (d)	105	cm	Target to detector distance
EMP Field Estimation (Peak-to-Peak)	~25	kV/m	Measured in vacuum chamber
Effective Dynamic Range	~74	dB	Achieved using calibrated splitter
Waveguide Cutoff Frequency (f_cutoff)	4.395	GHz	For TE₁₁ mode rejection in TOF pipe

Key Methodologies

The successful implementation of the advanced TOF scheme relied on precise material selection and rigorous EMP management techniques:

Detector Fabrication: A 50 µm intrinsic CVD diamond layer was grown on a 0.5 mm HPHT substrate. The detector utilized a planar interdigital configuration with 20 µm wide/spaced aluminum contacts, optimized for fast time detection.
High Dynamic Range Acquisition: The raw signal was split 50/50 using a calibrated splitter and recorded simultaneously on two channels of a 1 GHz, 10 Gs/s oscilloscope (LECROY HDO 4104) set to different amplitude scales, maximizing the effective dynamic range to capture both intense and fine signal details.
EMP Mitigation (Near-Field): The diamond detector was housed in a compact cylindrical metallic enclosure designed to minimize direct EMP coupling by leveraging a cutoff frequency principle, without obstructing the active surface.
EMP Mitigation (Far-Field/Transmission): The TOF line utilized a 65 cm long pipe (R_TOF = 20 mm) acting as a cylindrical waveguide, achieving high rejection of EMP fields traveling in the vacuum chamber (f_cutoff = 4.395 GHz).
Signal Isolation: The signal was transmitted via 15 m double-shielded RG223 coaxial cables, surrounded by multiple ferrite toroids (0.5 MHz - 1 GHz bandwidths) to damp external EMP currents on the cable shield.
Signal De-embedding: A frequency-domain de-embedding procedure was applied to the recorded signal V(t) using the measured S₂₁ scattering parameter of the entire transmission line (cables, splitter, bias tee) to recover the true signal S_D(t) at the detector site.
Spectrum Calibration: The Charge Collection Efficiency (CCE) of the diamond detector was experimentally calibrated using proton beams (0.3 MeV to 2 MeV) and incorporated into the analytical spectrum reconstruction methodology to accurately determine the number of detected particles.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-performance CVD diamond materials and custom engineering required to replicate, optimize, and scale the advanced TOF detector scheme described in this research.

Applicable Materials

The core innovation relies on ultra-thin, high-quality diamond layers for fast response and high energy resolution.

Optical Grade Single Crystal Diamond (SCD): Required for the active layer (50 µm intrinsic diamond) due to its superior carrier mobility, fast time response (Δt < 1 ns), and exceptional radiation hardness. 6CCVD offers SCD wafers with thickness control from 0.1 µm up to 500 µm, ensuring precise replication of the 50 µm layer used in this study.
High Purity Substrates: We provide high-quality diamond substrates (up to 10 mm thickness) suitable for epitaxial growth or as robust mechanical supports for thin active layers, matching the HPHT substrate used in the experiment.

Customization Potential

The proposed stacked detector architecture and the specific interdigital contact geometry demand high-precision customization, which is a 6CCVD specialty.

Requirement from Paper	6CCVD Customization Capability	Value Proposition
Thin Layer Stacking: Need for multiple thin (50-100 µm) modules.	Precision Thickness Control: Supply matched sets of SCD wafers with uniform thickness (e.g., 50 µm ± 1 µm) and high parallelism (Ra < 1 nm polishing).	Enables the scalable, stacked architecture for simultaneous high sensitivity and resolution.
Interdigital Contacts: 20 µm width/spacing Al contacts on 4x4 mm area.	Custom Metalization & Lithography: In-house capability for depositing and patterning metals (Au, Pt, Pd, Ti, W, Cu, and Al) with micron-level precision for interdigital or planar electrode geometries.	Ensures optimal charge collection and fast signal readout for TOF applications.
Detector Dimensions: 4 mm x 4 mm.	Custom Dimensions & Laser Cutting: We provide plates and wafers up to 125 mm (PCD) and offer precision laser cutting services to achieve exact dimensions (e.g., 4x4 mm) required for compact mounting and EMP shielding enclosures.	Facilitates integration into complex, space-constrained vacuum chambers and diagnostic systems.

Engineering Support

6CCVD’s in-house PhD team specializes in material science and detector physics for extreme environments. We can assist researchers and engineers with:

Material Selection: Optimizing the SCD/PCD grade and thickness based on specific ion energy ranges (e.g., tailoring thickness to ensure full stopping or specific energy loss for high-energy protons).
Detector Design: Consulting on electrode geometry, metalization stack, and surface preparation (Ra < 1 nm polishing for SCD) to maximize Charge Collection Efficiency (CCE) and minimize noise in Laser-Plasma Ion Diagnostics projects.
EMP Mitigation Strategies: Providing material specifications that inherently resist EMP coupling, complementing the external shielding techniques described in this paper.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-021-82655-w

References

2013 - A Superintense Laser-Plasma Interaction Theory Primer [Crossref]
2013 - Laser-Plasma Interactions and Applications, Scottish Graduate Series
2009 - The Physics of Inertial Fusion, Beam Plasma Interaction, Hydrodynamics