Direct laser acceleration of electrons in free-space

Compact laser-driven accelerators are versatile and powerful tools of unarguable relevance on societal grounds for the diverse purposes of science, health, security, and technology because they bring enormous practicality to state-of-the-art achievements of conventional radio-frequency accelerators. Current benchmarking laser-based technologies rely on a medium to assist the light-matter interaction, which impose material limitations or strongly inhomogeneous fields. The advent of few cycle ultra-intense radially polarized lasers has materialized an extensively studied novel accelerator that adopts the simplest form of laser acceleration and is unique in requiring no medium to achieve strong longitudinal energy transfer directly from laser to particle. Here we present the first observation of direct longitudinal laser acceleration of non-relativistic electrons that undergo highly-directional multi-GeV/m accelerating gradients. This demonstration opens a new frontier for direct laser-driven particle acceleration capable of creating well collimated and relativistic attosecond electron bunches and x-ray pulses

Development of new FRP reinforcement for optimized concrete structures

With the goal of achieving sustainable design, being able to combine optimized geometries with durable construction materials is a major challenge for Civil Engineering. Recent research at the University of Bath has demonstrated that fibre-reinforced polymers (FRP) can be woven into geometrically appropriate cages for the reinforcement of optimised concrete beams. This innovative construction method enables the replacement of conventional steel with non-corrosive reinforcement that can provide the required strength exactly where needed. The manufacturing of the reinforcement is achieved by means of an automated process based on a filament winding technique. Being extremely lightweight, the wound-FRP (WFRP) cages are well suited to speeding up construction processes, as they can be delivered on site ready to be cast. In this paper, the results of flexural tests on optimised full-scale flexibly formed concrete elements are reported and discussed. Two different case studies are taken in consideration: A structurally optimized joist supporting a lightweight floor;A structurally optimized beam with an in-situ casting of a concrete floor. The optimization objective is to obtain the minimal mass of concrete required to achieve the structural capacity design requirements from widely recognized design codes. The experimental results demonstrate the reliability of the technical solution proposed and provide the basis of a new concept for sustainable and durable reinforced concrete structures

Filament winding fabrication of FRP reinforcement cages

This project has made progress towards the development of a novel alternative reinforcement technique for concrete structures with complex geometries, which are difficult to reinforce with conventional steel. Fibre-reinforced polymers (FRP) are woven into geometrically appropriate reinforcement cages to provide the required strength exactly where it is needed. Automated fabrication of the reinforcement utilises a modification of the filament winding technique. Being extremely lightweight, the resulting wound- FRP (W-FRP) cages are well suited to automation of the construction process, as they can be delivered ready for casting in optimized concrete elements. This is a key advance in research progress towards achieving minimum embodied energy, optimised, concrete structures. Experimental tests conducted on full-size W-FRP reinforced concrete beams demonstrate the reliability of the solution proposed, showing a new frontier for sustainable and durable reinforced concrete structures

Terahertz-driven linear electron acceleration

The cost, size and availability of electron accelerators is dominated by the achievable accelerating gradient. Conventional high-brightness radio-frequency (RF) accelerating structures operate with 30-50 MeV/m gradients. Electron accelerators driven with optical or infrared sources have demonstrated accelerating gradients orders of magnitude above that achievable with conventional RF structures. However, laser-driven wakefield accelerators require intense femtosecond sources and direct laser-driven accelerators and suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing requirements due to the short wavelength of operation. Here, we demonstrate the first linear acceleration of electrons with keV energy gain using optically-generated terahertz (THz) pulses. THz-driven accelerating structures enable high-gradient electron or proton accelerators with simple accelerating structures, high repetition rates and significant charge per bunch. Increasing the operational frequency of accelerators into the THz band allows for greatly increased accelerating gradients due to reduced complications with respect to breakdown and pulsed heating. Electric fields in the GV/m range have been achieved in the THz frequency band using all optical methods. With recent advances in the generation of THz pulses via optical rectification of slightly sub-picosecond pulses, in particular improvements in conversion efficiency and multi-cycle pulses, increasing accelerating gradients by two orders of magnitude over conventional linear accelerators (LINACs) has become a possibility. These ultra-compact THz accelerators with extremely short electron bunches hold great potential to have a transformative impact for free electron lasers, future linear particle colliders, ultra-fast electron diffraction, x-ray science, and medical therapy with x-rays and electron beams

Estimating local records for Northern and Central Italy from a sparse secular temperature network and from 1961–1990 climatologies

The paper presents monthly 30-arc-second-resolution Northern and Central Italy temperature climatologies and discusses the procedure we adopt to superimpose the information of temperature secular records onto these climatologies. The climatologies are obtained by means of a step-wise linear regression method which aims at determining the temperature dependence on geographical and morphological variables. Such a method is applied to a database of about 800 monthly 1961–1990 temperature normals. In the first regression (temperature vs. elevation) the recorded data are considered; the further regressions concern the residuals obtained after taking into account the effect of each variable, in order of importance. An estimated secular anomaly record can be obtained for each point of the climatology grid by means of a distance-weighted average of the temperature anomaly records of the stations surrounding the grid point