280 research outputs found
The Cold Waters in the Port of Genoa (NW Mediterranean Sea) during the Marine Heatwave in Summer 2022
No full textExtreme weather phenomena have become more frequent and intense in recent decades in the context of climate change, and these include heat waves that affect both the atmosphere and seawater masses. In 2022, a summer marine heatwave (MHW) affected the entire Mediterranean Sea, and temperatures up to 5 °C above seasonal mean were reached in the Ligurian Sea in the NW part of the Mediterranean basin. In this scenario, the waters of the Port of Genoa (at the northern apex of the Ligurian Sea) distinguished themselves by maintaining lower temperatures than those of the open sea (a maximum gradient of −6.1 °C on 9 August 2022) after the passage of a fast-moving storm. In this study, the weather and sea parameters of the period (June–December 2022) are analysed to determine the phenomenon that caused the drop in temperatures in the water masses of the Port of Genoa. The sudden cooling of the water masses inside the port was caused by a heavy rainfall event in early August. Moreover, the isolation of the port water masses due to the weak dynamics of the period kept them stationary and locked inside the port. Seawater temperatures inside the port slowly rose again after the event, remaining cooler than outside temperatures throughout August (−0.3 °C on 31 August), reaching and exceeding outside temperatures on 3 September (26.4 °C), and remaining warmer until 3 November 2022 (21.5 °C)
Plasma Production by Laser Ablation of Heavy Metals
No full textAn Nd:YAG focused laser operating at 1064 nm, 3 ns pulse width, 360 mJ pulse energy, is employed to irradiate heavy metals, such as Ta, W, Pt, Au, and Pb. The in-vacuum irradiation produces an expanding plasma at the target surface which has high density, temperature, and kinetic energy of emitted ions. Ions have a velocity of the order of 104 m/s with a charge state up to about 10+ and large ion energy distribution from some eV up to values of the order of some keV. The measurements of the ion emission, their velocity, and energy have been performed using a Faraday cup ion collector connected in time-of-flight (TOF) configuration. The ion energy, charge state, and energy distributions were performed using a cylindrical electrostatic ion deflector (IEA) with high energy resolution. The measurements are investigated and compared with literature and theoretical prediction models
Six MeV proton acceleration from plasma generated by high-intensity laser using advanced thin polyethylene targets
No full textProton acceleration can be induced by non-equilibrium plasma developed by high-intensity laser pulses, at 1016 W/cm2, irradiating different types of thin polyethylene targets. The process of proton acceleration and directive yield emission was investigated, optimizing the laser parameters, the irradiation conditions, and the target properties. The use of 600 J pulse energy, a laser focalization inducing self-focusing effects and advanced targets with embedded nanoparticles and optimal thicknesses, has permitted to accelerate forward protons up to the energies of about 6 MeV and amount of the order of 1015 H+/pulse. High proton energy is obtained using thin foils enriched with gold nanoparticles, whereas high proton yield is obtained using targets with a thickness of about 10 μm. The plasma diagnostics using SiC semiconductor detectors in time-of-flight configuration was fundamental to monitor the optimal conditions to improve the plasma processes concerning the ion acceleration and the X-ray and relativistic electron emission
Tantalum ion acceleration in laser-generated plasma and dependence on the pulse duration
No full textThe laser irradiation of tantalum targets is presented for different pulsed laser intensities ranging from 1010 up to about 1018 W/cm2 and pulse durations from 9 ns up to 40 fs. The results show that the produced non-equilibrium plasma accelerates Ta ions in the backward direction from values of the order of keV up to values of about 5 MeV. In thin foils, the forward plasma, developed behind the target along the direction of incoming laser, at intensities of about 1016 W/cm2 and 300 ps pulse duration, accelerates Ta ions at energies of the order of 4.6 MeV and produces charge states up to about 40+. For fs lasers at intensities of the order of 1018 W/cm2, only proton acceleration occurs up to 2.1 MeV while no Ta ions are accelerated, due to the reduced duration of the electric field and to the too high inertial mass of the Ta ions
Protons and carbon ions acceleration in the target-normal-sheath-acceleration regime using low-contrast fs laser and metal-graphene targets
Get PDFfs pulsed lasers at an intensity of the order of 1018 W/cm2, with a contrast of 10−5, were employed to irradiate thin foils to study the target-normal-sheath-acceleration (TNSA) regime. The forward ion acceleration was investigated using 1/11 μm thickness foils composed of a metallic sheet on which a thin reduced graphene oxide film with 10 nm thickness was deposited by single or both faces. The forward-accelerated ions were detected using SiC semiconductors connected in time-of-flight configuration. The use of intense and long pre-pulse generating the low contrast does not permit to accelerate protons above 1 MeV because it produces a pre-plasma destroying the foil, and the successive main laser pulse interacts with the expanding plasma and not with the overdense solid surface. Experimental results demonstrated that the maximum proton energies of about 700 keV and of 4.2 MeV carbon ions and higher were obtained under the condition of the optimal acceleration procedure. The measurements of ion energy and charge states confirm that the acceleration per charge state is measurable from the proton energy, confirming the Coulomb–Boltzmann-shifted theoretical model. However, heavy ions cannot be accelerated due to their mass and low velocity, which does not permit them to be subjected to the fast and high developed electric field driving the light-ion acceleration. The ion acceleration can be optimized based on the laser focal positioning and on the foil thickness, composition, and structure, as it will be presented and discussed
Laser-generated Cu plasma in vacuum and in nitrogen gas
No full textA pulsed ns IR laser at about 1010 W/cm2 intensity is employed to irradiate a Cu target placed in a vacuum and in nitrogen gas. The produced plasma is characterized in terms of emitted ions and photons as a function of the nitrogen pressure in the chamber. The mechanisms of ion gas interactions are investigated in terms of Cu ion energy loss and X-ray attenuation using an ion collector and a SiC detector. A fast CCD camera in the visible region has produced the collision images of the ions with the nitrogen molecules. A plasma temperature of about 44 eV, an emission of soft X-rays up to about 100 eV, an ablation yield of about 2.4 × 1015 atoms/pulse, a maximum Cu ion acceleration of 1.4 keV and a maximum ionization up to Cu9+ were measured in high vacuum
THE NEPHELOID BOTTOM LAYER AND THE DYNAMICS OF THE WATER MASSES AT THE SHELF-BREAK OF THE WESTERN ROSS SEA
No full textIn the austral summers of 2000/2001 and 2002/2003 the Italian CLIMA Project carried out two oceanographic cruises along the northwestern margin of the Ross Sea, where the Antarctic Bottom Water forms. Here there is an interaction between the water masses on the sea floor of the outer shelf and slope with a consequent evolution of benthic nepheloid layers and an increase in total particulate matter. We observed three different situations:(a)the presence of triads (bottom structures characterized by a concomitant jump in turbidity, temperature, and salinity data) and high re- suspension phenomena related to the presence of the Circumpolar Deep Water and its mixing with cold, salty shelf waters associated with gravity currents;(b)the absence of triads with highre-suspension, implying that when the gravity currents are no longer active the benthic nepheloid layer may persist until the suspended particles settle to the seafloor, suggesting that the turbidity data can be used to study recent gravity current events;and(c) the absence of turbidity and sediment e-suspension phenomena supports the theory that as teady situation had been re-established and the current interaction no longer occurred or had finished some time before
Eight MeV per charge state from 300 ps laser ion acceleration by using micrometric foils
No full textProton acceleration using high-intensity laser pulses, at 1016 W/cm2 was studied irradiating different types of thin metal and plastic targets having 1-micron thickness. The maximization of the proton energy process was investigated optimizing the laser parameters, the irradiation conditions and the target properties. Employing 600–700 J laser pulse energy, a focalization inducing self-focusing effects and using targets with optimized thickness, it was possible to accelerate protons up to energies of above 8 MeV. The time-of-flight diagnostics has allowed to monitor the plasma properties and to control the ion acceleration process
First Attempt to Study Sedimentological Characteristics and Contamination Levels of Bottom Sediments in the Faanu Mudugau Blue Hole (Ari Atoll, Maldives)
No full textEnvironmental contamination is ubiquitous and even in the ocean, signs of contamination of different types (chemical, biological, or plastic) are detected in all kinds of environments. In this study, a sediment core was sampled at the bottom of the Blue Hole of the Maldives (Ari Atoll) to make a first characterization of the sediment in terms of its grain size and organic–inorganic matter composition and to assess the sediment contamination levels in terms of trace elements (by ICP-MS analysis) and the eventual presence of microplastics (by optical classification and microRaman analysis of items). High concentrations of Hg (a maximum value of 0.145 ppm at the bottom layer of the core), Cd (a maximum value of 0.65 ppm at the core surface layer), and As (9.4 ppm at the top of the core) were highlighted at different layers of the sediment core. Plastic polymers were not detected in the sediment core, but 51 fibers characterized by the presence of artificial dyes or additives were found in the core (a mean of 5.7 fibers for each slice). The results confirmed the sediment contamination of the Maldivian Blue Hole, supporting the hypothesis of contamination due to ineffective waste management within the archipelago and mass tourism affecting the atolls
Cold electrons acceleration in TNSA laser-generated plasma using a low-contrast fs laser
No full textThe fs laser facility in Bordeaux, delivering an intensity of 1018 W/cm2 at normal incidence on thin foils, has been used to induce forward electron and ion acceleration in target-normal-sheath-acceleration (TNSA) regime. Micrometric thin foils with different composition, thickness, and electron density, were prepared to promote the charge particle acceleration in the forward direction. The plasma electron and ion emission monitoring were performed on-line using SiC semiconductor detectors in time-of-flight (TOF) configuration and gaf-chromics films both covered by thin absorber filters. The experiment has permitted to accelerate electrons and protons. A special attention was placed to detect relativistic hot electrons escaping from the plasma and cold electrons returning to the target position. The electron energies of the order of 100 keV and of about 1 keV were detected as representative of hot and cold electrons, respectively. A high cold electron contribution was measured using low-contrast fs laser, while it is less evident using high-contrast fs lasers. The charge particle acceleration depends on the laser parameters, irradiation conditions, and target properties, as will be presented and discussed
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