69 research outputs found
Investigation of jet formation from the blast wave of a locally heated laser-irradiated target
No full textAbstractA possible mechanism responsible for the formation of jets observed near young stellar objects is thought to involve conically converging flows which are generated when the stellar wind encounters an inward facing shock at an oblique angle. While this mechanism of inertial collimation has been verified by simulations, it is not accessible to direct observations due to the small scales on which it operates. Until recently, laboratory experiments have only been able to reproduce the second part of the mechanism by directly creating a converging conical flow to produce a jet. In this contribution we present a conceptual numerical study proposing an new configuration to create jets that are able to reproduce both stages of the mechanism, including the inward facing reverse shock, from simple initial conditions. By selectively heating a small region inside a target, irradiated by a high-intensity laser pulse, a jet can be created inside the plasma behind the rear target surface. We present three dimensional simulations of the formation of the jet. We find jets with aspect ratios of over 15 and Mach numbers between 2.5 and 4.3. The influence of simulation parameters is investigated and the applicability of the jets to their astrophysical counterparts is discussed
Fast Electron Transport Study for Inertial Confinement Fusion
No full textUn nouveau mod`ele r´eduit pour le transport de faisceaux d’´electrons relativistes dans des solide ou des plasma denses est propos´e. Il est bas´e sur la r´esolution des deux premiers moments angulaires de l’´equation cin´etique relativiste, compl´et´es par une relation de fermeture d´eduite du principe de maximisation de l’entropie angulaire de Minerbo. Le mod`ele prend en compte aussi bien les effets collectifs du transport avec les champs ´electromagn´etiques auto g´en´er´es que les effets collisionnels li´es au ralentissement des ´electrons par collision sur les plasmons, les ´electrons li´es et les ´electrons libres du milieu ainsi que leur diffusion angulaire par collisions sur les ´electrons et les ions. Le mod`ele permet une r´esolution num´erique rapide des ´equations du transport de faisceau d’´electrons rapides tout en d´ecrivant l’´evolution cin´etique de leur fonction de distribution. Malgr´e le fait de travailler avec les grandeurs angulaires moyennes, le mod`ele a ´et´e valid´e par comparaison avec des solutions analytiques d´eriv´ees dans un cas acad´emique de transport de faisceau mono ´energ´etique et collimat´e dans un plasma dense et chaud d’Hydrog`ene ainsi qu’avec une simulation PIC hybride dans un cas r´ealiste de transport d’´electrons acc´el´er´es par laser dans une cible solide. Le mod`ele est appliqu´e `a l’´etude de l’´emission de photons Kα lors d’exp´eriences laser-plasma ainsi qu’a` la g´en´eration d’ondes de choc.A new hybrid reduced model for relativistic electron beam transport in solids and dense plasmas is presented. It is based on the two first angular moments of the relativistic kinetic equation completed with the Minerbo maximum angular entropy closure. It takes into account collective effects with the self-generated electromagnetic fields as well as collisional effects with the slowing down of the elec- trons in collisions with plasmons, bound and free electrons and their angular scattering on both ions and electrons. This model allows for fast computations of relativistic electron beam transport while describing the kinetic distribution function evolution. Despite the loss of information concerning the angular distribution of the electron beam, the model reproduces analytical estimates in the academic case of a collimated and monoenergetic electron beam propagating through a warm and dense Hydro- gen plasma and hybrid PIC simulation results in a realistic laser-generated electron beam transport in a solid target. The model is applied to the study of the emission of Kα photons in laser-solid experiments and to the generation of shock waves
Spectral control in proton acceleration with multiple laser pulses
No full textWe address the question of whether multiple high intensity (> 10(18) W cm(-2)) laser pulses ( each O( 100 fs)) can produce proton beams with a modified energy spectrum on irradiating a foil target. This has been studied in one dimension with both Vlasov and particle-in-cell codes. A reduction in the maximum proton energy, and the generation of spectral peaks, is observed. This is the first theoretical demonstration of spectral peak generation by purely optical means. The mechanism, which has been termed multiple pulse sheath acceleration, that produces these spectral peaks is described, and the same mechanism occurs in both sets of simulations
Multiple pulse sheath acceleration : an optical approach to spectral control
No full textRecent experimental results have shown that it is possible to produce laser-accelerated proton and ion beams with distinct quasi-monoenergetic features in the energy spectrum [1, 2]. As short-pulse ultraintense laser intensities exceed 1021Wcm−2, it may be possible to produce quasi-monoenergetic proton bunches with energies in the range of 100-200 MeV. This opens up the prospect of a new route to developing medical ion accelerators for oncology. In this paper we will briefly report on some of our recent work [3]. This showed that it is theoretically possible to produce laser-accelerated proton/ion beams with distinct spectral peaks by irradiating a solid target with two laser pulses that arrive in rapid succession. No special target composition or structure is required, unlike the other schemes that have been proposed [1, 2]. This may be advantageous for certain applications
Vorticity deposition, structure generation and the approach to self-similarity in colliding blast wave experiments
No full textAbstractWhen strong shocks interact with transverse density gradients, it is well known that vorticity deposition occurs. When two non-planar blast waves interact, a strong shock will propagate through the internal structure of each blast wave where the shock encounters such density gradients. There is therefore the potential for the resulting vorticity to produce pronounced density structures long after the passage of these shocks. If the two blast waves have evolved to the self-similar (Sedov) phase this is not a likely prospect, but for blast waves at a relatively early stage of their evolution this remains possible. We show, using 2D numerical simulations, that the interactions of two ‘marginally young’ blast waves can lead to strong vorticity deposition which leads to the generation of a strong protrusion and vortex ring as mass is driven into the internal structure of the weaker blast wave
A nature-based solution for sustainable port development in Port of Kuala Tanjung, Indonesia
No full textThe Building with Nature (BwN) approach developed by Ecoshape suggests that nature-based solutions can be sustainable and cost-effective alternatives for traditional engineering solutions. Widening the solution space by studying and understanding the physical and ecological system in the early stages of port planning and design is more likely to result in sustainable ports with opportunities for multi-functionality and respect for nature. This paper applies the BwN philosophy to a case study, i.e., the ongoing port development in Kuala Tanjung in Indonesia and examines the technical and financial feasibility of a nature-based concept, i.e., a mangrove breakwater instead of a traditional 'hard' breakwater. Mangroves can realize significant wave attenuation, and at the same time, they are productive eco-systems that can result in long-term benefits through multifunctional land use. A berm built of dredged material with a mild slope which 'grows' naturally by accretion behind permeable dams can create the right conditions for mangrove trees to grow. This mangrove protection can develop into a sustainable barrier which grows with the (relative) sea level rise by trapping sediments. A preliminary design was made on the basis of information available in literature. A rough cost comparison considering only the supply and placing of fill material showed that mangrove breakwater is about 25percent more expensive than a hard breakwater for the case under study. In view of the numerous port projects being planned in Indonesia, the technical and financial feasibility of mangrove breakwaters that can also enhance nature create added value for the surroundings is a promising finding.Rivers, Ports, Waterways and Dredging Engineerin
Fast Electron Transport Study for Inertial Confinement Fusion
No full textUn nouveau mod`ele r´eduit pour le transport de faisceaux d’´electrons relativistes dans des solide ou des plasma denses est propos´e. Il est bas´e sur la r´esolution des deux premiers moments angulaires de l’´equation cin´etique relativiste, compl´et´es par une relation de fermeture d´eduite du principe de maximisation de l’entropie angulaire de Minerbo. Le mod`ele prend en compte aussi bien les effets collectifs du transport avec les champs ´electromagn´etiques auto g´en´er´es que les effets collisionnels li´es au ralentissement des ´electrons par collision sur les plasmons, les ´electrons li´es et les ´electrons libres du milieu ainsi que leur diffusion angulaire par collisions sur les ´electrons et les ions. Le mod`ele permet une r´esolution num´erique rapide des ´equations du transport de faisceau d’´electrons rapides tout en d´ecrivant l’´evolution cin´etique de leur fonction de distribution. Malgr´e le fait de travailler avec les grandeurs angulaires moyennes, le mod`ele a ´et´e valid´e par comparaison avec des solutions analytiques d´eriv´ees dans un cas acad´emique de transport de faisceau mono ´energ´etique et collimat´e dans un plasma dense et chaud d’Hydrog`ene ainsi qu’avec une simulation PIC hybride dans un cas r´ealiste de transport d’´electrons acc´el´er´es par laser dans une cible solide. Le mod`ele est appliqu´e `a l’´etude de l’´emission de photons Kα lors d’exp´eriences laser-plasma ainsi qu’a` la g´en´eration d’ondes de choc.A new hybrid reduced model for relativistic electron beam transport in solids and dense plasmas is presented. It is based on the two first angular moments of the relativistic kinetic equation completed with the Minerbo maximum angular entropy closure. It takes into account collective effects with the self-generated electromagnetic fields as well as collisional effects with the slowing down of the elec- trons in collisions with plasmons, bound and free electrons and their angular scattering on both ions and electrons. This model allows for fast computations of relativistic electron beam transport while describing the kinetic distribution function evolution. Despite the loss of information concerning the angular distribution of the electron beam, the model reproduces analytical estimates in the academic case of a collimated and monoenergetic electron beam propagating through a warm and dense Hydro- gen plasma and hybrid PIC simulation results in a realistic laser-generated electron beam transport in a solid target. The model is applied to the study of the emission of Kα photons in laser-solid experiments and to the generation of shock waves
Laser particle acceleration
No full textThe production of highly energetic beams of both electrons and ions is a major part of the experimental programme at the Central Laser Facility (CLF), STFC Rutherford Appleton Laboratory. Every year sees a significant number of experiments done in both areas. This has been complemented by theoretical studies that have been carried out at the CLF and UK universities. In a recent consultation on plans to build a 10 PW upgrade to the VULCAN facility, laser-driven particle acceleration formed a very significant part of the science case that emerged from this consultation. In this talk, I will review the experimental progress that has been made in particle acceleration, and I will also examine what theoretical investigations suggest the future of this field will be. Experimental studies of laser-driven ion acceleration of the CLF using both the VULCAN and ASTRA systems have looked at a number of aspects including focussing and control of the ion beam, manipulation of the energy spectrum, energy scaling with laser and target parameters, and direct use of the proton beam in both isochoric heating of secondary targets and proton radiography. Recently there has been great interest in a number of theoretical studies which indicate that it should be possible to explore radiation-pressure driven ion acceleration for intensities above 1021 Wcm-2, which will be accessible with the ASTRA-GEMINI system. This very exciting prospect will also be discussed. Electron acceleration in laser wakefields is also a well established part of the CLF programme. Experimental studies of laser-driven electron acceleration using the ASTRA laser have explored electron acceleration in both supersonic gas jets and gas-filled capillaries. This has led to the production of electron bunches with up to 1 GeV energy and a few percent energy spread. The influence of tuneable parameters such as the evolution of the plasma channel inside a capillary or the position of the laser focus with respect to the gas jet is actively being investigated. These efforts are backed up by a matching numerical campaign. Recent experiments have also shown that electron bunches trapped on a downward density ramp can have a very small absolute energy spread, and the potential consequences of these results will also be discussed. © 2011 Optical Society of America
Late Cretaceous and Tertiary subsidence history of the Sirte Basin (Libya): an example of the use of backstripping analysis
No full textThe results of a quantitative analysis of subsidence data from 20 wells covering six major basement blocks of the Sirte Basin (Libya) are presented. Tectonic subsidence curves were calculated from the stratigraphic record using backstripping techniques; these were subsequently used to derive subsidence rates in time. Extension started in the Late Cretaceous, followed by four distinguishable tectonic phases. The onset of extension coincided with the change of the Africa-to-Europe relative motion vector from eastward to westward. Intraplate stress variations and resulting isostatic rebound and downwarping of the lithosphere caused differential fault tectonics and regional uplift and subsidence during the Palaeocene-late Eocene. Termination of this phase in the late Eocene was a result of the change to westward plate motion of Africa. Subsidence and marine deposition continued until the early Miocene, when the stress regime changed to NW-SE compressional as a result of the pronounced northward movement of Africa relative to Europe. -Author
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