103 research outputs found
Gravitational-Wave Stochastic Background from Kinks and Cusps on Cosmic Strings
We compute the contribution of kinks on cosmic string loops to stochastic
background of gravitational waves (SBGW).We find that kinks contribute at the
same order as cusps to the SBGW.We discuss the accessibility of the total
background due to kinks as well as cusps to current and planned gravitational
wave detectors, as well as to the big bang nucleosynthesis (BBN), the cosmic
microwave background (CMB), and pulsar timing constraints. As in the case of
cusps, we find that current data from interferometric gravitational wave
detectors, such as LIGO, are sensitive to areas of parameter space of cosmic
string models complementary to those accessible to pulsar, BBN, and CMB bounds.Comment: 24 pages, 3 figure
Optimisation of Thin Plastic Foil Targets for Production of Laser-Generated Protons in the GeV Range
In order to realistically simulate the interaction of a femtosecond laser
pulse with a nanometre-thick target it is necessary to consider a target
preplasma formation due to the nanosecond long amplified-spontaneous-emission
pedestal and/or prepulse. The relatively long interaction time dictated that
hydrodynamic simulations should be employed to predict the target particles'
number density distributions prior the arrival of the main laser pulse. By
using the output of the hydrodynamic simulations as input into particle-in-cell
simulations, a detailed understanding of the complete laser-foil interaction is
achieved. Once the laser pulse interacts with the preplasma it deposits a
fraction of its energy on the target, before it is either reflected from the
critical density surface or transmitted through an underdense plasma channel. A
fraction of hot electrons is ejected from the target leaving the foil in a net
positive potential, which in turn results in proton and heavy ion ejection. In
this work protons reaching ~25 MeV are predicted for a laser of ~40 TW peak
power and ~600 MeV are expected from a ~4 PW laser system.Comment: 17 pages, 21 figure
On production and asymmetric focusing of flat electron beams using rectangular capillary discharge plasmas
A method for the asymmetric focusing of electron bunches, based on the active
plasma lensing technique is proposed. This method takes advantage of the strong
inhomogeneous magnetic field generated inside the capillary discharge plasma to
focus the ultrarelativistic electrons. The plasma and magnetic field parameters
inside the capillary discharge are described theoretically and modeled with
dissipative magnetohydrodynamic computer simulations enabling analysis of the
capillaries of rectangle cross-sections. Large aspect ratio rectangular
capillaries might be used to transport electron beams with high emittance
asymmetries, as well as assist in forming spatially flat electron bunches for
final focusing before the interaction point.Comment: 16 pages, 7 figures, 1 tabl
Plasma Equilibrium inside Various Cross-Section Capillary Discharges
Plasma properties inside a hydrogen-filled capillary discharge waveguide were
modeled with dissipative magnetohydrodynamic simulations to enable analysis of
capillaries of circular and square cross-sections implying that square
capillaries can be used to guide circularly-symmetric laser beams. When the
quasistationary stage of the discharge is reached, the plasma and temperature
in the vicinity of the capillary axis has almost the same profile for both the
circular and square capillaries. The effect of cross-section on the electron
beam focusing properties were studied using the simulation-derived magnetic
field map. Particle tracking simulations showed only slight effects on the
electron beam symmetry in the horizontal and diagonal directions for square
capillary.Comment: 6 pages, 10 figure
Laser beam coupling with capillary discharge plasma for laser wakefield acceleration applications
One of the most robust methods, demonstrated up to date, of accelerating
electron beams by laser-plasma sources is the utilization of plasma channels
generated by the capillary discharges. These channels, i.e., plasma columns
with a minimum density along the laser pulse propagation axis, may optically
guide short laser pulses, thereby increasing the acceleration length, leading
to a more efficient electron acceleration. Although the spatial structure of
the installation is simple in principle, there may be some important effects
caused by the open ends of the capillary, by the supplying channels etc., which
require a detailed 3D modeling of the processes taking place in order to get a
detailed understanding and improve the operation. However, the discharge
plasma, being one of the most crucial components of the laser-plasma
accelerator, is not simulated with the accuracy and resolution required to
advance this promising technology. In the present work, such simulations are
performed using the code MARPLE. First, the process of the capillary filling
with a cold hydrogen before the discharge is fired, through the side supply
channels is simulated. The main goal of this simulation is to get a spatial
distribution of the filling gas in the region near the open ends of the
capillary. A realistic geometry is used for this and the next stage
simulations, including the insulators, the supplying channels as well as the
electrodes. Second, the simulation of the capillary discharge is performed with
the goal to obtain a time-dependent spatial distribution of the electron
density near the open ends of the capillary as well as inside the capillary.
Finally, to evaluate effectiveness of the beam coupling with the channeling
plasma wave guide and electron acceleration, modeling of laser-plasma
interaction was performed with the code INF&RNOComment: 11 pages, 9 figure
Laser-heated capillary discharge plasma waveguides for electron acceleration to 8 GeV
A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ≈ 1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments
Non-adiabatic cluster expansion after ultrashort laser interaction
AbstractWe used X-ray spectroscopy as a diagnostic tool for investigating the properties of laser-cluster interactions at the stage in which non-adiabatic cluster expansion takes place and a quasi-homogeneous plasma is produced. The experiment was carried out with a 10 TW, 65 fs Ti:Sa laser focused on CO2 cluster jets. The effect of different laser-pulse contrast ratios and cluster concentrations was investigated. The X-ray emission associated to the Rydberg transitions allowed us to retrieve, through the density and temperature of the emitting plasma, the time after the beginning of the interaction at which the emission occurred. The comparison of this value with the estimated time for the "homogeneous" plasma formation shows that the degree of adiabaticity depends on both the cluster concentration and the pulse contrast. Interferometric measurements support the X-ray data concerning the plasma electron density
RISK ASSESSMENT MODELS OF PUBLIC-PRIVATE PARTNERSHIP IN THE ROAD SECTOR
This article studies the main potential models of public-private partnership; it gives evaluation of risks for these models, considering their distribution between members of partnership. It offers the mechanism of making an optimal choice of a public-private partnership model for projects of transport system development
QUANTITATIVE ASSESSMENT OF THE INVESTMENT PROJECT CREATION OR RENOVATION TRANSPORT INFRASTRUCTURE
Summary. The paper proposes a method of determining the quantitative assessment of the investment project of reconstruction of the facility or transport infrastructure, taking into account the impact on both the vehicle and non-transport effect. Among the most significant socio- economic benefits of modernization and development of the road network of the federal and regional significance include: improving and improving and improving the social conditions of the population , increased economic activity , reduction of transport costs in the price of goods and services, reducing the negative impact of transport and road complex environment. Modelling of toxic pollutant emissions for the transport stream to optimize road to reconstruct existing infrastructure by minimizing environmental damage. Kinematic model of traffic flow, which allows to express the parameters of toxic pollution through directly observable quantities, based on the concept of cellular automata , augmented parameters governing the organization of traffic. Necessary to determine the parameters of motion so that the average flow rate was in the optimal range (60 - 90) km / h. Multicriteria optimization problem so requires collecting and analyzing vast and diverse information of the following types: topographic, demographic, social, economic, environmental, transport. As follows from the calculations, the doses of all types of toxic effects, per unit length of the road, increase significantly in the fall an average speed of traffic flow. Thus, modeling of toxic emissions transport stream allows one hand to optimize the traffic in the existing infrastructure and, on the other hand, to optimize the construction and reconstruction of infrastructure
- …