Search

The quality of electron bunches accelerated by laser wakefields is highly dependant on the temporal and spatial features of the laser driver. Analysis of experiments performed at APOLLON PW-class laser facility shows that spatial instabilities of the focal spot, such as shot-to-shot pointing fluctuations or asymmetry of the transverse fluence, lead to charge and energy degradation of the accelerated electron bunch. It is shown that PIC simulations can reproduce experimental results with a significantly higher accuracy when the measured laser asymmetries are included in the simulated laser's transverse profile, compared to simulations with ideal, symmetric laser profile. A method based on a modified Gerchberg–Saxton iterative algorithm is used to retrieve the laser electric field from fluence measurements in vacuum in the focal volume, and accurately reproduce experimental results using PIC simulations, leading to simulated electron spectra in close agreement with experimental results, for the accelerated charge, energy distribution, and pointing of the electron beam at the exit of the plasma. [ABSTRACT FROM AUTHOR]

This paper uses the capability approach to analyse renewable energy developments on Aboriginal land in Australia's Pilbara and Kimberley regions. These regions in the north-west of Australia have very high rates of Indigenous land tenure, and are attractive for both solar and wind power generation, particularly as developing technology makes it economically feasible to transport power over large distances. They are also remote from Australia's electricity networks and often rely on expensive fossil fuels for electricity generation. Resident Aboriginal communities are among the most income-poor in Australia yet live in regions rich in renewable energy. Their ability to benefit from the opportunities offered by a transition to renewable sources of energy varies according to a number of factors. This paper examines the conditions under which Indigenous capabilities may be enhanced or inhibited, through examining three scales of energy generation: large-scale developments for export; remote utility-owned networks; and small-scale standalone off-grid applications. This paper will ask what capabilities can Indigenous people achieve from a just approach to a renewable energy transition in northern Australia, and what capabilities are required in order to gain maximum benefit from this current rapid energy transition? [ABSTRACT FROM AUTHOR]

Presents a study which computed analytically the tail of the electron distribution function, including the radial and axial diffusion, in a plasma generated by an electron beam of a few keV. Determination of the ionization efficiency of the tail electrons in creating bulk electrons; Comparison of the asymptotic behavior that results for large axial distances with experimental data for molecular oxygen plasma; Conclusion.

Examines the enhanced plasma stopping of energetic multicharged ions by inserting a fully ionized hydrogen column on a tandem accelerator ion beam line. Relevance to heavy ion driven inertial compression; Concept of the enhanced plasma stopping; Framework of the ion-plasma interaction.

The evolutionary effects of harvest on wild fish populations have been documented around the world; however, sublethal selective pressures can also cause evolutionary changes in phenotypes. For migratory fishes, passage facilities may represent instances of nonlethal selective pressure. Our analysis of 6 years of passage data suggests that certain fish passage facilities on the Penobscot River have been exerting selective pressure against large-bodied, anadromous Atlantic salmon ( Salmo salar). At the second and third dams in the river, a 91-cm salmon was 21%-27% and 12%-16% less likely to pass than a 45-cm salmon, respectively. Fish size positively influences egg survival and number and is a heritable trait. Therefore, in a wild-reproducing population, exclusion of large fish from spawning areas may have population-level impacts. In the Penobscot River, most returning adults derive from a hatchery program that collects its broodstock after passing the first dam in the river. Analysis of fork lengths of salmon returning to the Penobscot River from 1978 to 2012 provided mixed support for evolution of size at maturity in different age classes in a pattern that may be expected from interactions with conservation hatchery operations. Additionally, slow-maturing and iteroparous individuals that represent the largest salmon size classes were essentially lost from the population during that time, and Penobscot River fish have shorter fork lengths at maturity than Atlantic salmon in undammed systems. [ABSTRACT FROM AUTHOR]

Ionization-induced electron injection was investigated experimentally by focusing a driving laser pulse with a maximum normalized potential of 1.2 at different positions along the plasma density profile inside a gas cell, filled with a gas mixture composed of 99%H2 þ 1%N2. Changing the laser focus position relative to the gas cell entrance controls the accelerated electron bunch properties, such as the spectrum width, maximum energy, and accelerated charge. Simulations performed using the 3D particle-in-cell code WARP with a realistic density profile give results that are in good agreement with the experimental ones. The interest of this regime for optimizing the bunch charge in a selected energy window is discussed. [ABSTRACT FROM AUTHOR]

The dynamics of ionization-induced electron injection in high density (~1.2 × 1019 cm-3) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism. [ABSTRACT FROM AUTHOR]

Numerical modeling of laser wakefield electron acceleration inside a gas filled dielectric capillary tube is presented. Guiding of a short pulse laser inside a dielectric capillary tube over a long distance (∼1 m) and acceleration of an externally injected electron bunch to ultra-relativistic energies (∼5-10 GeV) are demonstrated in the quasi-linear regime of laser wakefield acceleration. Two dimensional axisymmetric simulations were performed with the code WAKE-EP (Extended Performances), which allows computationally efficient simulations of such long scale plasma. The code is an upgrade of the quasi-static particle code, WAKE [P. Mora and T. M. Antonsen, Jr., Phys. Plasmas 4, 217 (1997)], to simulate the acceleration of an externally injected electron bunch (including beam loading effect) and propagation of the laser beam inside a dielectric capillary. The influence of the transverse electric field of the plasma wake on the radial loss of the accelerated electrons to the dielectric wall is investigated. The stable acceleration of electrons to multi-GeV energy with a non-resonant laser pulse with a large spot-size is demonstrated. [ABSTRACT FROM AUTHOR]

For the considered scheme of the external electron bunch injection in front of a laser pulse, the influence of the nonlinear driving laser pulse dynamics and electron bunch self-action to the processes of electron bunch compression and acceleration in the laser wakefield is analyzed. Self-consistent modelling results confirm that the nonlinear laser pulse dynamics limits the bunch compression due to variations of the phase velocity of the wake. A growth of the injected bunch charge leads to some extent to an increase of the trapped and accelerated bunch charge and to decrease of the trapped bunch radius and emittance due to increased self-focusing bunch. The three-dimensional theoretical model is elaborated and used to describe the propagation of laser pulses in dielectric capillary waveguides under imperfect coupling and focusing conditions with broken cylindrical symmetry. The role of cone entrances to the cylindrical part of a capillary is analyzed, and it is demonstrated that matching cones can considerably increase the transmission of laser pulses through the capillary, but cannot mitigate the requirements on the precision of the laser pulse focusing into a capillary. In order to avoid a speckle structure and strong transverse gradients of the fields, which can prevent the process of regular electron bunch acceleration, one has to ensure a small laser angle of incidence into the capillary not exceeding 1 mrad. [ABSTRACT FROM AUTHOR]

We present three-dimensional modeling of amplification of a high-order harmonic seed by a soft x-ray laser plasma. The time-dependent evolution of the x-ray signal is determined from a fully dynamic Maxwell-Bloch calculation. At high seed intensities, a simplified one-dimensional calculation leads to strong Rabi-like temporal oscillations of the output signal. However, such oscillations have not been observed experimentally. Our calculations demonstrate that this is due to spatial non-uniformities in the plasma gain that cause the Rabi oscillations to dampen dramatically. Large amplitude Rabi-like oscillations are expected to appear only in long and uniform plasma. Such targets require optimized guiding techniques. [ABSTRACT FROM AUTHOR]

The dynamics of electron acceleration by laser wakefield and the associated x-rays emission in long plasmas are numerically investigated for parameters close to the threshold of laser self-focusing. The plasma length is set by the use of dielectric capillary tubes that confine the gas and the laser energy. Electrons self-injection and acceleration to the 170 MeVs are obtained for densities as low as 5 × 1018 cm-3 and a moderate input intensity (0.77 × 1018 W/cm2). The associated x-ray emission at the exit of the capillary tube is shown to be an accurate diagnostic of the electrons self-injection and acceleration process. [ABSTRACT FROM AUTHOR]

This article is based on a collaborative evaluation of the implementation of a Libraries and Knowledge Centre (LKC) model in three remote Indigenous communities in the Northern Territory. It outlines the context in which LKC services are being implemented, provides a brief description of the LKC model, and discusses some strengths of the model to deliver relevant and sustainable services to Indigenous communities in these changing times. The article highlights some of the more challenging issues that emerge in such a complex knowledge and information context, as well as issues relating to the broader challenges in delivering sustainable services in remote Indigenous communities in the current policy context. [ABSTRACT FROM AUTHOR]

The theory and simulations of short intense laser pulses propagating in capillary tubes, whose properties are changed in time and space under the action of the laser field, are presented. A hybrid approach has been used in which the dynamics of fields inside the capillary tube is described analytically, whereas the ionization, heating, and expansion of the plasma created at the inner wall of the tube under the action of the transverse energy flux are calculated by numerical simulation. This hybrid method has allowed to determine the behavior of high laser fluxes guided over large distances. The threshold value for the incident intensity at which plasma creation plays a significant role has been estimated analytically and confirmed by numerical results. For intensities above the threshold, the transmission becomes highly sensitive to the energy of the laser pulse, being minimum at the intensity level for which the electron temperature of the capillary wall slightly exceeds the Fermi level and the electron collision frequency has a maximum. [ABSTRACT FROM AUTHOR]

We present the status of optical field ionization soft X-ray lasers. The amplifying medium is generated by focusing a high-energy circularly polarized 30-fs 10-Hz Ti: sapphire laser system in a gaseous medium. Using xenon or krypton, strong laser emission at 41.8 and 32.8 nm, respectively, has been observed. After presenting the basis of the physics, we present recent characterization of the sources as well as dramatic improvement of their performances using the waveguiding technique. [ABSTRACT FROM PUBLISHER]

Single, double and triple ionization cross-sections of C n + clusters in collisions with helium atoms at intermediate velocity (2.6 a.u.) have been measured ( n = 1 → 5). The relative multi-ionization cross-sections (double over single and triple over single) are first increasing with n, then decreasing when going from n = 4 to n = 5. We show, on the basis of an independent atom and electron collisional treatment, that this effect is attributable to a change in the cluster shape. The role of the cluster compactness on relative multi-ionization cross-sections is pointed out here for the first time. [ABSTRACT FROM AUTHOR]

Derives Thomas-Fermi approaches to thermodynamics and atomic physics properties of dense and ionized matter consisting of a single element. Comparison with a density-functional theoretical framework; Emphasis on equations of state, ionization, level shifts and radial moments; Thermonuclear fusion stress out density.

Influence of target temperature, density and atomic number on the charge state of swift heavy ions interacting with hot and dense plasma is considered. Hydrogen targets exhibit strong temperature effects and large non-equilibrium charges, whereas interactions with heavy material are more sensitive to the density effect. Our new average correlated hydrogenic atom model (ACHAM) is presented. It enables us to cover the whole range of target densities of interest for swift heavyion-plasma interaction experiments. [ABSTRACT FROM AUTHOR]

Charge exchange of chlorine ions traversing a discharge plasma target is used as a probe to determine the rati of heavy impurities inside a plasma column. The rate coefficient of the recombination process is strongly related to the atomic number of the target atoms. High- Z impurities are much more efficient to modify the charge state distribution of the incoming chlorine ions. The ragne of detection could reach about 1‰ of the total number of atoms. [ABSTRACT FROM AUTHOR]

Extraordinary nonprofit-sector expansion has produced organizations with complex missions and operations, and the managers responsible for their effectiveness require adequate preparation. Although no single degree program stands out as the clear preference of nonprofit executives, we propose that certain organizational characteristics are associated with the preference for specific degrees. [ABSTRACT FROM AUTHOR]