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

Executive Summary

This research details a novel Time-of-Flight (TOF) diagnostic scheme utilizing Chemical Vapor Deposition (CVD) diamond detectors, specifically engineered for high-energy, high-intensity laser-plasma experiments characterized by extreme Electromagnetic Pulse (EMP) pollution.

Core Achievement: Successful acquisition of accurate, calibrated proton spectra up to ~2.5 MeV in a highly EMP-polluted environment (2 x 10¹⁹ W/cm² laser intensity) with high signal-to-noise ratio.
EMP Mitigation Strategy: Achieved high EMP rejection through a combination of optimized analog signal management, including a cylindrical waveguide structure (f_cutoff = 4.395 GHz) and long, double-shielded coaxial cables (15 m RG223) acting as low-pass filters (625 MHz bandwidth).
High Fidelity Data: A signal splitting technique was implemented, routing the detector output to two oscilloscope channels at different vertical scales, ensuring capture of both high-amplitude peaks and fine temporal details necessary for accurate time-of-flight analysis.
Data Processing Innovation: A frequency-dependent cable de-embedding procedure was applied to recover the true detector signal, correcting for attenuation introduced by the long transmission line.
Spectrum Accuracy: The methodology incorporates experimental calibration of the diamond detector’s Charge Collection Efficiency (CCE) as a function of incident proton energy, enabling precise particle number estimation.
Future Development: The work validates the use of a single module, paving the way for advanced stacked diamond detector configurations to simultaneously achieve high sensitivity and high energy resolution for highly energetic ions.

Technical Specifications

Parameter	Value	Unit	Context
Laser Wavelength	800	nm	FLAME Ti:Sapphire laser
Laser Peak Power	100	TW	Nominal maximum power
Laser Intensity (Max)	2 x 10¹⁹	W/cm²	Maximum intensity on target
Laser Pulse Duration	30	fs	Ultra-short pulse duration
TOF Flight Path (d)	105	cm	Target to detector distance
Detector Material	CVD Diamond	N/A	Monocrystalline, interdigital configuration
Diamond Active Layer Thickness	50	µm	Intrinsic layer thickness
Electron-Hole Pair Energy (ε)	13	eV	Energy required to create a pair in diamond
Max Proton Energy Measured	~2.5	MeV	Achieved with high accuracy
EMP Waveguide Cutoff (f_cutoff)	4.395	GHz	Cylindrical pipe (R_TOF = 20 mm)
Coaxial Cable Length	15	m	RG223 double-shielded
Coaxial Cable Bandwidth (3 dB)	625	MHz	Effective low-pass filtering
Max Estimated EMP Field	~25	kV/m	Peak-to-peak electric field inside chamber
Proton Energy Conversion Ratio (R_L-p)	0.4	%	Estimated for the pure proton energy range

Key Methodologies

Detector and TOF Line Shielding: The CVD diamond detector was housed in a compact cylindrical metallic enclosure with a minimal aperture. The TOF line utilized a 65 cm long pipe (R_TOF = 20 mm) acting as a cylindrical waveguide to achieve high-frequency EMP rejection (f_cutoff = 4.395 GHz).
Analog Signal Management: The detector output was connected via 15 m RG223 double-shielded coaxial cables to the oscilloscope. These cables provided both physical distance (reducing direct EMP coupling to the scope) and acted as low-pass filters (625 MHz bandwidth). Ferrite toroids were placed around the cables to damp external EMP currents.
Dynamic Range Optimization: The signal was split 50/50 using a calibrated splitter and recorded simultaneously on two oscilloscope channels (Ch1 and Ch3) set to different vertical scales. This ensured that both the high-amplitude particle signal and the low-amplitude photopeak details were captured without saturation.
Absolute Time Reference Determination: The narrow photopeak (generated by UV-X rays at the laser-matter interaction instant) was used as the absolute time reference (t_ph). The interaction time (t₀) was calculated as t_ph minus the photon propagation time (Δt_prop = d/c).
Cable De-embedding Procedure: The frequency-dependent attenuation of the transmission line (S₂₁ parameter) was measured offline using a Vector Network Analyzer. This data was used in a Fourier Transform-based de-embedding procedure to recover the true detector signal S_D(t), correcting for signal distortion and attenuation.
Detector Calibration (CCE): The Charge Collection Efficiency (CCE) of the diamond detector was experimentally calibrated using proton beams (0.3 MeV to 2 MeV) at the AN2000 microbeam facility. This CCE curve was essential for accurately converting the measured charge (Q_i) into the number of detected particles (N_i).
Spectrum Calculation: The energy (E_i) of the detected ions was calculated from the time-of-flight (TOF) using non-relativistic formulas. The number of particles (N_i) was calculated using the de-embedded charge signal, the CCE curve, and the electron-hole pair creation energy (13 eV).

Commercial Applications

The developed EMP-hardened, high-resolution TOF diagnostic system is critical for applications requiring accurate particle characterization in environments dominated by intense electromagnetic interference.

Inertial Confinement Fusion (ICF) and High-Energy Physics: Essential diagnostics for next-generation high-power laser facilities (e.g., ELI, PETAL) where high EMP levels are inherent, enabling real-time monitoring of accelerated ions and fusion products.
Laser-Plasma Acceleration (LPA): Provides the capability for high-repetition rate, accurate spectral characterization of laser-accelerated proton and ion beams, crucial for optimizing acceleration mechanisms (TNSA, RPA).
Medical Hadron Therapy: Used in the development and monitoring of laser-driven particle sources for medical applications, requiring precise, high-resolution dosimetry and beam characterization in complex environments.
Radiation Hardened Sensing: The methodology validates the use of thin, stacked CVD diamond detectors, known for high radiation hardness, in high-flux, high-EMP environments, suitable for nuclear safety and security applications.
Advanced Sensor Development: The techniques for EMP rejection and signal de-embedding are directly applicable to other fast, time-resolved solid-state detectors (e.g., SiC) used in harsh electromagnetic environments.

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