Effect of Bohm potential on a charged gas

Bohm's interpretation of Quantum Mechanics leads to the derivation of a Quantum Kinetic Equation (QKE): in the present work, propagation of waves in charged quantum gases is investigated starting from this QKE. Dispersion relations are derived for fully and weakly degenerate fermions and bosons (these latter above critical temperature), and the differences underlined. Use of a kinetic equation permits investigation of "Landau-type" damping: it is found that the presence of damping in fermion gases is dependent upon the degree of degeneracy, whereas it is always present in boson gases. In fully degenerate fermions a phenomenon appears that is akin to the "zero sound" propagation.Comment: 11 pages, no figures, pdf forma

Growth and equilibrium size of water droplets in air

A model is presented to describe the growth in time of the average water drop in supersaturated air, and predict their radius at equilibrium. Many previous works consider the growth of an isolated drop, whereas in the present work the effect of the presence of a large number of drops, with the ensuing depletion in water content in the surrounding air, is considered: it is shown that the effect of depletion is crucial to obtain the equilibrium radius. Preliminary results, obtained under some simplifying assumptions, are presented: expressions accounting for this depletion effect are given for the time evolution of the liquid-water temperature and of the number of water molecules in the drop and drop radius near equilibrium, and for their asymptotic equilibrium values

Analysis of unmitigated large break loss of coolant accidents using MELCOR code

In the framework of severe accident research activity developed by ENEA, a MELCOR nodalization of a generic Pressurized Water Reactor of 900 MWe has been developed. The aim of this paper is to present the analysis of MELCOR code calculations concerning two independent unmitigated large break loss of coolant accident transients, occurring in the cited type of reactor. In particular, the analysis and comparison between the transients initiated by an unmitigated double-ended cold leg rupture and an unmitigated double-ended hot leg rupture in the loop 1 of the primary cooling system is presented herein. This activity has been performed focusing specifically on the in-vessel phenomenology that characterizes this kind of accidents. The analysis of the thermal-hydraulic transient phenomena and the core degradation phenomena is therefore here presented. The analysis of the calculated data shows the capability of the code to reproduce the phenomena typical of these transients and permits their phenomenological study. A first sequence of main events is here presented and shows that the cold leg break transient results faster than the hot leg break transient because of the position of the break. Further analyses are in progress to quantitatively assess the results of the code nodalization for accident management strategy definition and fission product source term evaluation

Plasmonic lenses for tunable ultrafast electron emitters at the nanoscale

Simultaneous spatiotemporal confinement of energetic electron pulses to femtosecond and nanometer scales is a topic of great interest in the scientific community, given the potential impact of such developments across a wide spectrum of scientific and industrial applications. For example, in ultrafast electron scattering, nanoscale probes would enable accurate maps of structural dynamics in materials with nanoscale heterogeneity, thereby leading to an understanding of the role of boundaries and defects on macroscopic properties. On the other hand, advances in this field are mostly limited by the brightness and size of the electron source. We present the design, fabrication, and optical characterization of bullseye plasmonic lenses for next-generation ultrafast electron sources. Using electromagnetic simulations, we examine how the interplay between light-plasmon coupling, plasmon propagation, dispersion, and resonance governs the properties of the photoemitted electron pulse. We also illustrate how the pulse duration and strength can be tuned by geometric design and predict that sub-10-fs pulses with nanoscale diameter can be achieved. We then fabricate lenses in gold films and characterize their plasmonic properties using cathodoluminescence spectromicroscopy, demonstrating suitable plasmonic behavior for ultrafast nanoscale photoemission

Beam diagnostics for charge and position measurements in ELI-NP GBS

The advanced source of Gamma-ray photons to be built in Bucharest (Romania), as part of the ELI-NP European Research Infrastructure, will generate photons by Compton back-scattering in the collision between a multi-bunch electron beam and a high intensity recirculated laser pulse. An S-Band photoinjector and the following C-band Linac at a maximum energy of 720MeV, under construction by an European consortium (EurogammaS) led by INFN, will operate at 100Hz repetition rate with trains of 32 electron bunches, separated by 16ns and a 250pC nominal charge. The different BPMs and current transformers used to measure transverse beam position and charge along the LINAC are described. Design criteria, production status and bench test results of the charge and position pickups are reported in the paper, together with the related data acquisition systems

Experimental Evaluation of the RF Shielding Properties of a Thin Resistive Layer in a Ceramic Chamber

In order to better understand the RF shielding properties of a thin resistive layer inside a ceramic vacuum chamber, an experimental set-up has been installed in the Electron Positron Accumulator (EPA) at CERN. A 500 MeV single bunch of about 7 x 1010 electrons (rms s=1 ns) is extracted into this dedicated beam line at a repetition rate of about 1 Hz. Wideband magnetic field probes are installed on the outer surfaces of a resistively coated ceramic test chamber as well as on a reference non-coated chamber located 2.5 m downstream the line. At the end of the extraction line, the beam passes through a thin Aluminum foil and is absorbed in an external dump. The experimental layout and the first results are presented. A comparison with theoretical expectations as well as possible implications for future machines are also discussed

Intense terahertz pulses from SPARC-LAB coherent radiation source

The linac-based Terahertz source at the SPARC_LAB test facility is able to gene rate highly intense Terahertz broadband pulses via coherent transition radiation (CTR) from high brightness electron beams. The THz pulse duration is typically down to 100 fs RMS and can be tuned through the electron bunch duration and shaping. The measured stored energy in a single THz pulse has reached 40 μ J, which corresponds to a peak electric field of 1.6 MV/cm at the THz focus. Here we present the main features, in particular spatial and sp ectral distributions and energy characterizations of the SPARC_LAB THz source, which is very competitive for investigations in Condensed Matter, as well as a valid tool for electron beam longitudinal diagnostics