arXiv subjects

M. Bernardini

Publications and source records attributed to M. Bernardini.

8 recordsLinked to original sources

arXiv2022

The inefficiency of stellar feedback in driving galactic outflows in massive galaxies at high redshift

Recent observations indicate that galactic outflows are ubiquitous in high redshift galaxies, including normal star forming galaxies, quasar hosts, and dusty star forming galaxies (DSFGs). However, the impact of outflows on the evolution of their hosts is still an open question. Here, we analyse the star formation histories (SFH) and galactic outflow properties of galaxies in massive haloes ($10^{12}M_{\odot} 4$ DSFGs, with SFRs of $\sim 1000\ M_{\odot}\rm yr^{-1}$ and molecular gas masses of $M_{\rm mol}\sim 10^{10}\ M_{\odot}$. However, the simulated galaxies are characterised by higher circular velocities than those observed in high-z DSFGs. The mass loading factors from stellar feedback are of the order of $\sim 0.1$, implying that stellar feedback is inefficient in driving galactic outflows and gas is consumed by star formation on much shorter time-scales than it is expelled from the interstellar medium (ISM). We also find that stellar feedback is highly inefficient in self-regulating star formation in this regime, with an average integrated star formation efficiency (SFE) per dynamical time of $30\%$. Finally, compared to FIRE-2 galaxies hosted in similarly massive haloes at lower redshift, we find lower mass loading factors and higher SFEs in the high redshift sample. We argue that both effects originate from the higher total and gas surface densities that characterise high$-z$ massive systems.

astro-ph.GA↗

arXiv2019

Flow dynamics and wall-pressure signature in high-Reynolds number overexpanded nozzle with free shock separation

A delayed detached eddy simulation (DDES) of an overexpanded nozzle flow with shock-induced separation is carried out at a Reynolds number equal to 1.7 10^7. The flow unsteadiness, characterised by self-sustained shock oscillations, induces local unsteady loads on the nozzle wall as well as global off-axis forces. A clear physical understanding of the driving factors of the unsteadiness is still lacking. Under the current conditions, the nozzle operates in a highly-overexpanded regime and comprises a conical separation shock within the nozzle contour, merging into a Mach disk in the nozzle centre. Our current study focuses on the unsteady pressure signature on the nozzle wall, through the use of Fourier-based spectral analysis performed in time and in the azimuthal wavenumber space. The numerical data well agrees with the experimental measurements in terms of mean and fluctuating wall pressure statistics. The frequency spectra are characterised by the presence of a large bump in the low frequency range associated to a breathing motion of the shock system and a broad and high amplitude peak at high frequencies generated by the turbulent activity of the detached shear layer. Moreover, a distinct peak at an intermediate frequency (of the order 1000 Hz) is observed to persist in the wall-pressure spectra along the nozzle wall. The analysis of the pressure signals in the azimuthal wavenumber space indicates that this peak is clearly associated to the first (non-symmetrical) pressure mode and it is thus connected to the generation of side loads. Furthermore, it is found that the unsteady Mach disk is characterised by an intense vortex shedding activity and the interaction of these vortices with the second shock cell is a key factor in the sustainment of an aeroacoustic feedback loop within the nozzle.

physics.flu-dyn↗

arXiv2019

Experimental observation of proton bunch modulation in a plasma, at varying plasma densities

We give direct experimental evidence for the observation of the full transverse self-modulation of a relativistic proton bunch propagating through a dense plasma. The bunch exits the plasma with a density modulation resulting from radial wakefield effects with a period reciprocal to the plasma frequency. We show that the modulation is seeded by using an intense laser pulse co-propagating with the proton bunch which creates a relativistic ionization front within the bunch. We show by varying the plasma density over one order of magnitude that the modulation period scales with the expected dependence on the plasma density.

physics.acc-ph↗

arXiv2018

Acceleration of electrons in the plasma wakefield of a proton bunch

High energy particle accelerators have been crucial in providing a deeper understanding of fundamental particles and the forces that govern their interactions. In order to increase the energy or reduce the size of the accelerator, new acceleration schemes need to be developed. Plasma wakefield acceleration, in which the electrons in a plasma are excited, leading to strong electric fields, is one such promising novel acceleration technique. Pioneering experiments have shown that an intense laser pulse or electron bunch traversing a plasma, drives electric fields of 10s GV/m and above. These values are well beyond those achieved in conventional RF accelerators which are limited to ~0.1 GV/m. A limitation of laser pulses and electron bunches is their low stored energy, which motivates the use of multiple stages to reach very high energies. The use of proton bunches is compelling, as they have the potential to drive wakefields and accelerate electrons to high energy in a single accelerating stage. The long proton bunches currently available can be used, as they undergo self-modulation, a particle-plasma interaction which longitudinally splits the bunch into a series of high density microbunches, which then act resonantly to create large wakefields. The AWAKE experiment at CERN uses intense bunches of protons, each of energy 400 GeV, with a total bunch energy of 19 kJ, to drive a wakefield in a 10 m long plasma. Bunches of electrons are injected into the wakefield formed by the proton microbunches. This paper presents measurements of electrons accelerated up to 2 GeV at AWAKE. This constitutes the first demonstration of proton-driven plasma wakefield acceleration. The potential for this scheme to produce very high energy electron bunches in a single accelerating stage means that the results shown here are a significant step towards the development of future high energy particle accelerators.

physics.acc-ph↗

arXiv2018

THESEUS: a key space mission concept for Multi-Messenger Astrophysics

The recent discovery of the electromagnetic counterpart of the gravitational wave source GW170817, has demonstrated the huge informative power of multi-messenger observations. During the next decade the nascent field of multi-messenger astronomy will mature significantly. Around 2030, third generation gravitational wave detectors will be roughly ten times more sensitive than the current ones. At the same time, neutrino detectors currently upgrading to multi km^3 telescopes, will include a 10 km^3 facility in the Southern hemisphere that is expected to be operational around 2030. In this review, we describe the most promising high frequency gravitational wave and neutrino sources that will be detected in the next two decades. In this context, we show the important role of the Transient High Energy Sky and Early Universe Surveyor (THESEUS), a mission concept proposed to ESA by a large international collaboration in response to the call for the Cosmic Vision Programme M5 missions. THESEUS aims at providing a substantial advancement in early Universe science as well as playing a fundamental role in multi-messenger and time-domain astrophysics, operating in strong synergy with future gravitational wave and neutrino detectors as well as major ground- and space-based telescopes. This review is an extension of the THESEUS white paper (Amati et al. 2017), also in light of the discovery of GW170817/GRB170817A that was announced on October 16th, 2017.

astro-ph.HE↗

arXiv2017

AWAKE readiness for the study of the seeded self-modulation of a 400\,GeV proton bunch

AWAKE is a proton-driven plasma wakefield acceleration experiment. % We show that the experimental setup briefly described here is ready for systematic study of the seeded self-modulation of the 400\,GeV proton bunch in the 10\,m-long rubidium plasma with density adjustable from 1 to 10$\times10^{14}$\,cm$^{-3}$. % We show that the short laser pulse used for ionization of the rubidium vapor propagates all the way along the column, suggesting full ionization of the vapor. % We show that ionization occurs along the proton bunch, at the laser time and that the plasma that follows affects the proton bunch. %

physics.plasm-ph↗

arXiv2015

AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world's first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected to sample the wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented.

physics.acc-ph↗

arXiv2015

Path to AWAKE: Evolution of the concept

This report describes the conceptual steps in reaching the design of the AWAKE experiment currently under construction at CERN. We start with an introduction to plasma wakefield acceleration and the motivation for using proton drivers. We then describe the self-modulation instability --- a key to an early realization of the concept. This is then followed by the historical development of the experimental design, where the critical issues that arose and their solutions are described. We conclude with the design of the experiment as it is being realized at CERN and some words on the future outlook. A summary of the AWAKE design and construction status as presented in this conference is given in [1].

physics.plasm-ph↗