arXiv subjects

Matteo Passoni

Publications and source records attributed to Matteo Passoni.

14 recordsLinked to original sources

arXiv2025

Impact of triangularity on edge transport and divertor detachment: a SOLPS-ITER study of TCV L-mode plasmas

Negative triangularity (NT) magnetic configurations have recently gained attention as a promising route to achieve H-mode-like confinement without edge-localized modes (ELMs) and without a power threshold for access. While both core and edge confinement properties of NT have been extensively documented, consistently lower divertor target cooling and increased difficulty in achieving a detached regime have been observed. This work presents a comparative SOLPS-ITER modeling study of two Ohmic L-mode discharges in the TCV tokamak with identical divertor geometry and opposite upper triangularity. We investigate whether magnetic geometry alone can account for the experimentally observed differences in plasma detachment behavior. Simulations with identical transport coefficients reveal no significant differences between NT and positive triangularity (PT) cases, even when including drifts. A parametric scan of radial anomalous transport coefficients shows that reproducing the experimental profiles requires lower particle diffusivity in NT, consistent with reduced turbulent transport and previous findings. Furthermore, the evolution of simulated neutral pressures and recycling fluxes along a density scan reproduces experimental observations of larger neutral divertor pressure in PT, highlighting a distinct neutral dynamics in the two cases. These results support the interpretation that altered cross-field transport, rather than magnetic geometry alone, underlies the observed differences in divertor behavior between NT and PT scenarios.

physics.plasm-ph↗

arXiv2025

Numerical proof-of-concept of a photon, proton, and positron laser-driven source with nanostructured targets

A source of high-energy photons, ions, and positrons can be attained with the interaction of ultra-intense femtosecond laser pulses with advanced nanostructured targets. We present and characterise a numerical model that mimics the foam deposition process on solid substrates, as it occurs in Double-Layer Target (DLT) manufacturing. The model is integrated into Particle-In-Cell (PIC) simulations in full 3D geometry to study electron acceleration, consequent high-energy photon emission, proton acceleration, and pair production with realistic target and laser parameters. We highlight the importance of realistic foam morphology modelling even at high-laser intensity and the need for specific optimisation of target parameters with realistic PIC simulations to improve radiation production efficiency. Our study shows that the DLT could be a compact multi-purpose scheme to achieve high-brightness photons and high-energy protons and to observe and optimise non-linear Breit-Wheeler pair production.

physics.plasm-ph↗

arXiv2021

Superintense Laser-driven Photon Activation Analysis

Laser-driven radiation sources are attracting increasing attention for several materials science applications. While laser-driven ions, electrons and neutrons have already been considered to carry out the elemental characterization of materials, the possibility to exploit high energy photons remains unexplored. Indeed, the electrons generated by the interaction of an ultra-intense laser pulse with a near-critical material can be turned into high energy photons via bremsstrahlung emission when shot into a high-Z converter. These photons could be effectively exploited to perform Photon Activation Analysis (PAA). In the present work, the possibility to perform laser-driven PAA is proposed and investigated. By means of a theoretical and numerical approach, we identify the optimal near-critical material and converter parameters for laser-driven PAA in a wide range of laser intensities. Finally, exploiting the Monte Carlo and Particle-In-Cell tools, we simulate PAA experiments performed with both conventional accelerators and laser-driven sources.

physics.plasm-ph↗

arXiv2020

Fractal Carbon nanofoams by nanosecond and femtosecond pulsed-laser deposition

We report on an investigation on the properties of ultra-low density, fractal, Carbon nanofoams fabricated with the nanosecond and femtosecond pulsed-laser deposition (PLD) techniques. We measure through innovative techniques the foam mean density and the properties of the fractal aggregates composing the film (i.e. nanoparticles diameter, fractal dimension, and gyration radius) as a function of several PLD process parameters, namely the background gas pressure and the laser pulse characteristics (energy, time duration, repetition rate). We discuss the experimental observation on the basis of the existing literature, and we propose an analytical equation, based on the fractal scaling law, to predict the foam density from the aggregates properties. Finally, we use analytical arguments to explain the observed trends in the nanofoam density with respect to the process parameters, useful to gain new insights on the nanofoam growth and to guide experimental work in fabricating ultra-low density films with precisely controlled properties.

cond-mat.mtrl-sci↗

arXiv2020

Role of energetic ions in the growth of fcc and {\omega} crystalline phases in Ti films deposited by HiPIMS

Titanium (Ti), due to its excellent properties, is widely exploited in thin film technology that usually leads to the production of {\alpha}-phase (hcp) Ti films. In this work, we investigate the phase evolution of Ti films deposited by varying type and energy of the film-forming species. To investigate different plasma species environments, films with different thicknesses are grown by using conventional Direct Current Magnetron Sputtering (DCMS) and High Power Impulse Magnetron Sputtering (HiPIMS). Furthermore, HiPIMS depositions with different substrate bias voltage US (0 V, -300 V and -500 V) are performed to investigate different ion energy ranges. Microstructure, morphology and residual stress of the deposited films, as well as the DCMS and HiPIMS plasma composition, are analysed with different characterization techniques. The DCMS samples exhibit the Ti {\alpha}-phase only and show a tensile residual stress decreasing with thickness. As far as HiPIMS samples are concerned, a compressive-tensile-compressive (CTC) behavior is observed for residual stresses as thickness increases. Specifically, films deposited in low energy ion conditions (US =0 V) show the presence of the Ti fcc phase up to a maximum thickness of about 370 nm. Differently, films deposited under high energy conditions (US = -300 V and -500 V) show the nucleation of the Ti {\omega}-phase for thicknesses greater than 260 and 330 nm, respectively. The formation of these unusual Ti phases is discussed considering the different deposition conditions.

cond-mat.mtrl-sci↗

arXiv2020

Post-mortem analysis of tungsten plasma facing components in tokamaks: Raman microscopy measurements on compact, porous oxide and nitride films and nanoparticles

Raman microscopy is one of the methods that could be used for future post-mortem analyses of samples extracted from ITER plasma facing. This study shows that this technique is useful for studying tungsten-based materials containing impurities including oxides and nitrides. Here, we apply pulsed laser deposition and DC argon glow discharges to produce tungsten-containing synthetic films (compact, porous) and nanoparticles and investigate the influence of their morphology on the measured Raman spectra. The amounts of oxygen and/or nitrogen in the films are also investigated. Comparative data are obtained by X-ray Photoelectrons Spectroscopy, Atomic Force Microscopy, Electron Microscopies (Scanning and Transmission), Energy Dispersive X-ray spectroscopy, Time-of-Flight Elastic Recoil Detection Analysis. The power density of the laser beam used to perform Raman microscopy is varied by up to 4 orders of magnitude (0.01-20 mW/$\mu$m 2) to investigate thermal stability of films and nanoparticles. As a first result, we give evidence that Raman microscopy is sensitive enough to detect surface native oxides. Secondly, more tungsten oxides are detected in porous materials and nanoparticles than in compact films, and the intensities of the Raman band correlate to their oxygen content. Thirdly, thermal stability of these films (i.e. structural and chemical modification under laser heating) is poor when compact films contain a sufficiently large amount of nitrogen. This finding suggests that nitrogen can be substituted by oxygen during Raman laser induced heating occurring in ambient air. Finally, our methodology can be used to rapidly characterize morphology and chemistry of the samples analyzed, and also to create oxides at the micrometer scale. keywords: PLD, Raman spectroscopy, tungsten oxide, tungsten nitride, plasma wall interaction, laser heating, post-mortem analysis 2

physics.chem-ph↗

arXiv2019

Superintense Laser-driven Ion Beam Analysis

Ion beam analysis techniques are among the most powerful tools for advanced material characterization. Despite their growing relevance in a widening number of fields, most ion beam analysis facilities still rely on the oldest accelerator technologies, with severe limitations in terms of portability and flexibility. In this work we thoroughly address the potential of superintense laser-driven proton sources for this application. We develop a complete analytical and numerical framework suitable to describe laser-driven ion beam analysis, exemplifying the approach for Proton Induced X-ray/Gamma-ray emission, a technique of widespread interest. This allows us to propose a realistic design for a compact, versatile ion beam analysis facility based on this novel concept. These results can pave the way for ground-breaking developments in the field of hadron-based advanced material characterization.

physics.plasm-ph↗

arXiv2019

Reference-free evaluation of thin films mass thickness and composition through energy dispersive x-ray spectroscopy

In this paper we report the development of a new method for the evaluation of thin films mass thickness and composition based on the Energy Dispersive X-Ray Spectroscopy (EDS). The method exploits the theoretical calculation of the in-depth characteristic X-ray generation distribution function, $\phi$/($\rho$ z), in multilayer samples, obtained by the numerical solution of the electron transport equation, to achieve reliable measurements without the need of a reference sample and multiple voltages acquisitions. The electron transport model is derived from the Boltzmann transport equation and it exploits the most updated and reliable physical parameters in order to obtain an accurate description of the phenomenon. The method for the calculation of film mass thickness and composition is validated with benchmarks from standard techniques. In addition, a model uncertainty and sensitivity analysis is carried out and it indicates that the mass thickness accuracy is in the order of 10 $\mu$g/cm$^2$, which is comparable to the nuclear standard techniques resolution. We show the technique peculiarities in one example measurement: two-dimensional mass thickness and composition profiles are obtained for a ultra-low density, high roughness, nanostructured film.

cond-mat.mtrl-sci↗

arXiv2018

Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

In this work, we investigate the correlation between morphology, composition, and the mechanical properties of metallic amorphous tungsten-oxygen and amorphous tungsten-oxide films deposited by Pulsed Laser Deposition. This correlation is investigated by the combined use of Brillouin Spectroscopy and the substrate curvature method. The stiffness of the films is strongly affected by both the oxygen content and the mass density. The elastic moduli show a decreasing trend as the mass density decreases and the oxygen-tungsten ratio increases. A plateaux region is detected in correspondence of the transition between metallic and oxide films. The compressive residual stresses, moderate stiffness and high local ductility that characterize compact amorphous tungsten-oxide films make them promising for applications involving thermal or mechanical loads. The coefficient of thermal expansion is quite high (i.e. 8.9 $\cdot$ 10$^{-6}$ K$^{-1}$), being strictly correlated to the amorphous structure and stoichiometry of the films. Under thermal treatments they show a quite low relaxation temperature (i.e. 450 K). They crystallize into the $\gamma$ monoclinic phase of WO$_3$ starting from 670 K, inducing an increase by about 70\% of material stiffness.

cond-mat.mtrl-sci↗

arXiv2017

Parametric investigation of laser interaction with uniform and nanostructured near-critical plasmas

Laser interaction with uniform and nanostructured near-critical plasmas has been investigated by means of 2D particle-in-cell simulations. The effect of a nanostructure (modeled as a collection of solid-density nanospheres) on energy absorption and radiative losses has been assessed in a wide range of laser intensities and average densities of the target. The nanostructure was found to affect mainly the conversion efficiency of laser energy into ion kinetic energy and radiative losses for the highest simulated intensities.

physics.plasm-ph↗

arXiv2017

Boron films produced by high energy Pulsed Laser Deposition

Micron-thick boron films have been deposited by Pulsed Laser Deposition in vacuum on several substrates at room temperature. The use of high energy pulses (>700 mJ) results in the deposition of smooth coatings with low oxygen uptake even at base pressures of 10$^{-4}$ - 10$^{-3}$ Pa. A detailed structural analysis, by X-Ray Diffraction and Raman, allowed to assess the amorphous nature of the deposited films as well as to determine the base pressure that prevents boron oxide formation. In addition the crystallization dynamics has been characterized showing that film crystallinity already improves at relatively low temperatures (800 {\deg}C). Elastic properties of the boron films have been determined by Brillouin spectroscopy. Finally, micro-hardness tests have been used to explore cohesion and hardness of B films deposited on aluminum, silicon and alumina. The reported deposition strategy allows the growth of reliable boron coatings paving the way for their use in many technology fields.

cond-mat.mtrl-sci↗

arXiv2015

Electron acceleration by relativistic surface plasmons in laser-grating interaction

The generation of energetic electron bunches by the interaction of a short, ultra-intense ($I>10^{19} \textrm{W/cm}^2$) laser pulse with "grating" targets has been investigated in a regime of ultra-high pulse-to-prepulse contrast ($10^{12}$). For incidence angles close to the resonant condition for Surface Plasmon (SP) excitation, a strong electron emission was observed within a narrow cone along the target surface, with energies exceeding 10 MeV. Both the energy and the number of emitted electrons were strongly enhanced with respect to simple flat targets. The experimental data are closely reproduced by three-dimensional particle-in-cell simulations, which provide evidence for the generation of relativistic SPs and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultra-short source of MeV electrons, these results are a step forward the development of high field plasmonics.

physics.plasm-ph↗

arXiv2013

Ion acceleration by superintense laser-plasma interaction

Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the potential for a number of foreseen applications and in the perspective to investigate novel regimes as far as available laser intensities will be increasing. Experiments have demonstrated in a wide range of laser and target parameters the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance and low emittance. In this paper we give an overview of the state-of-the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. We describe the main features observed in the experiments, the observed scaling with laser and plasma parameters and the main models used both to interpret experimental data and to suggest new research directions.

physics.plasm-ph↗

arXiv2011

Laser ion acceleration using a solid target coupled with a low density layer

We investigate by particle-in-cell simulations in two and three dimensions the laser-plasma interaction and the proton acceleration in multilayer targets where a low density "near-critical" layer of a few micron thickness is added on the illuminated side of a thin, high density layer. This target design can be obtained by depositing a "foam" layer on a thin metallic foil. The presence of the near-critical plasma strongly increases both the conversion efficiency and the energy of electrons and leads to enhanced acceleration of proton from a rear side layer via the Target Normal Sheath Acceleration mechanism. The electrons of the foam are strongly accelerated in the forward direction and propagate on the rear side of the target building up a high electric field with a relatively flat longitudinal profile. In these conditions the maximum proton energy is up to three times higher than in the case of the bare solid target.

physics.plasm-ph↗