Hybrid modeling of relativistic underdense plasma photocathode injectors

The dynamics of laser ionization-based electron injection in the recently introduced plasma photocathode concept is analyzed analytically and with particle-in-cell simulations. The influence of the initial few-cycle laser pulse that liberates electrons through background gas ionization in a plasma wakefield accelerator on the final electron phase space is described through the use of Ammosov-Deloine-Krainov theory as well as nonadiabatic Yudin-Ivanov (YI) ionization theory and subsequent downstream dynamics in the combined laser and plasma wave fields. The photoelectrons are tracked by solving their relativistic equations of motion. They experience the analytically described transient laser field and the simulation-derived plasma wakefields. It is shown that the minimum normalized emittance of fs-scale electron bunches released in mulit-GV/m-scale plasma wakefields is of the order of 10-2 mm mrad. Such unprecedented values, combined with the dramatically increased controllability of electron bunch production, pave the way for highly compact yet ultrahigh quality plasma-based electron accelerators and light source applications

Landbouw en ruimtelijke organisatie in Nederland : analyse en toekomstverkenning van een regionaal gedifferentieerde betrekking

PART ONE: RESEARCH FRAMEWORKThe rapid changes in Dutch agriculture since 1950 have had important spatial implications. Because agriculture makes such extensive claims on the space available in the Netherlands, these implications are evident in nearly all rural areas. Changes in the spatial requirements for agriculture, as much as its spatial effects, come readily to mind. In the past decades both have been of more or less intensive government concern in areas such as physical planning, land development, environmental policy, and regional economic policy. In the future too, the spatial requirements of agriculture and its effects will continue to need special attention. This is even more so, because the current process of agricultural reorientation will also have far reaching consequences for spatial organization. It is self evident that this is an important task for spatial planning and it is the reason for making the relationship between agriculture and spatial organization in the Netherlands a subject for analysis and reconnaissance.The spatial organization model developed by Kleefmann in particular, offers a way of coming to terms with the contents of this broad research area and allows discussion of the most important variables in the development of our physical environment and their relationships. This study follows, primarily, the distinction made in the model between societal and physical aspects of spatial organization. Questions concerning the spatial conditions for agriculture, its spatial effects, and government policy pursued in this connection are examined from both points of view.The main structure, methodologically, is provided by a differentiation into analysis and reconnaissance. Analysis extends from 1950, with the accent on the period after 1973. The reconnaissance extends to about the year 2010. Both these significant stages of the planning process are placed in the perspective of planning as an investigative instrument. Following this approach, plans function as tools in the process of investigating possible and worthwhile development directions for the future they are primarily intended to facilitate social and political discussion about the choice of course to be taken.Particular attention is given, in analysis and reconnaissance, to inter-regional differences in the relationship between agriculture and spatial organization. In part, these can be traced back to the large regional differences in agricultural development itself-, in part they are associated with social and physical factors outside agriculture. In this study, a large number of maps are used to stress the importance of the regionally differentiated character of the relationship between agriculture and spatial organization.PART TWO: ANALYSIS FROM THE SOCIETAL PERSPECTIVEWhen considering the relationship between agriculture and spatial organization from the societal perspective, attention is directed to the development of agriculture in relation to the location, extent and proximity of different societal functions and activities. Therefore, particular attention is paid to functions and activities which result from regional-economic development and urbanization, such as employment opportunities and housing.If the spatial requirements for agriculture are considered in this way, then it appears that the economically more developed regions, such as the West and South, offer comparative advantages for the development of intensive agricultural production such as glasshouse horticulture and intensive animal husbandry. These favourable conditions have contributed to the rapid growth of intensive production in these regions. However, there is another side to the spatial conditions offered to agriculture by the well-developed regions. Increasing the area for such dynamic production as glasshouse horticulture or bulb growing is becoming more difficult because of the growing spatial needs of urban complexes and the equally large and growing congestion within agriculture itself. Thus, further extension of the central function of agricultural complexes in these regions becomes increasingly difficult. The accessibility of farms and land consolidation also require attention from the societal perspective; these form the spatial context in which divergent activities within farm management are coordinated. In general accessibility appears unfavourable in the clay and peat areas, whilst in most sand areas, it is land consolidation that leaves the most to be desired. This, combined with the presence of small farms, has contributed to the rise of intensive production in the sand areas of the South, East and Centre of the country; a development that is most apparent in the southern sand area, which lies in a region already well-developed economically.If the societal perspective is used to consider the spatial effects of agriculture, then it appears that the regionally differentiated development of agriculture has clearly influenced the extent to which Dutch regional development problems have arisen. In agriculture, in all regions, there were indications of a considerable increase in labour productivity. In the more developed regions, increased labour productivity had been realized, to an important degree, by intensification, that is to say by increasing production per hectare. In the economically relatively poorly developed North, this occurred mainly by increasing the land - man ratio. Because of the relatively great significance of agriculture to northern employment it resulted in a considerable outflow of labour from agriculture there. In this way agriculture has not only been important in contributing to the persistent absence of work opportunities in this part of the country, it has also strengthened the process by which small rural centres have lost their function.From an analysis of regional differences in the spatial conditions for agriculture and the effects of agriculture, there seems to be a rough linkage between the development of agriculture in terms of intensity and land-man ratio on the one hand and the level of regional economic development and urbanization on the other. In general terms three zones can be differentiated on the basis of this linkage and, in these zones, linkages show themselves in different ways: a central zone, a peripheral zone and an intermediary zone. The spatial questions are most clearly defined in the central zone (urban-agrarian congestion) and in the periphery (problems of regional development).Questions arising from the regionally differentiated relationship between agriculture and spatial organization, such as mentioned above, have received very limited attention in government policy during the last decades. Measures to strengthen the regional economic development of the North were mainly directed towards stimulating industry and services. Possibilities of stimulating the regional economy through the development of intensive agriculture (hardly represented there) have, until recently, scarcely been taken into consideration. In the relatively rapidly developing regions, physical planning focused on the spatial conditions for safeguarding further agriculture development by clustering urbanization and preserving open space.PART THREE: ANALYSIS FROM THE PHYSICAL PERSPECTIVEIn considering the relationship between agriculture and spatial organization from the physical perspective, attention centres on the development of agriculture in relation to the physical capacity of the natural substrate, the manner in which this is transformed for and by agriculture and the implications of this for agriculture and other functions and activities. In the case of the latter, particular attention is given to nature conservation and to the recovery of drinking water from ground water.If the spatial requirements for agriculture are looked at in this way, then it appears that natural, regionally strongly differentiated spatial conditions for agriculture in a large part of the country have been altered mainly by intervention in the water balance. During the past decades, this has resulted in an improvement in the suitability of the soil for agriculture in many areas. It must be said, however, that reducing the importance of several of the soil suitability limitations has been achieved by a considerable increasing the purchase of concentrates and roughage within the animal husbandry sector. These intervention, on behalf of agriculture, in the natural substrate and changes in farming management have not had an entirely favourable influence on the spatial conditions for agriculture. Interventions in the water balance and the application of sprinkling in large sections of the higher parts of the Netherlands have contributed to the desiccation of sensitive cultivated land. In addition, intensive and one-sided land use has threatened soil fertility- this can also be seen most clearly in the higher parts of the Netherlands.If the physical perspective is used to consider the spatial effects of agriculture, then the negative aspects of the intensive way in which Dutch agriculture has developed in the last decades come sharply into focus. The nature and seriousness of problems are strongly differentiated regionally. The negative influences of agriculture on nature and the natural potential for drinking water recovery as a whole, apply particularly in the higher parts of the Netherlands. This can be attributed, to a large extent, to the concentration of types of agriculture which burden the natural substrate, such as intensive animal husbandry. But an important role is also played by the relatively great sensitivity of sand soil to processes such as desiccation, acidification, the leaching of nutrients and pesticides, and to the presence of sensitive ecosystems and freatic groundwater supply. In addition, in the higher parts of the Netherlands considerable differences appear in the number and seriousness of the problems caused by agriculture. Because of a lower concentration of animal production in the northern sand area, there is less overuse of manure and there is less acidification than in the Central, East and Southern sand areas. In the lower parts of the Netherlands, the negative effects of agriculture on nature and on possibilities for drinking water recovery are, as a whole, less serious although they do exist. One of the most obvious problem areas is the relationship between agriculture and nature in the peat pasture areas.From the results of the analysis, it appears that the distinction between the higher and lower parts of the Netherlands forms an important factor in regional differentiation in the relationship between agriculture and spatial organization. The biggest spatial problems occur in the higher parts of the Netherlands and particularly in the sand area. But within both these zones, there are stiff many differences in the relationship between agriculture and spatial organization. Within the higher parts of the Netherlands, the northern sand area occupies a favourable position relative to the other three.Problems in the relationship between agriculture and nature have been an important focus for government policy towards the rural areas in the last decades. As these problems became acute, influenced by a dynamic agriculture, there was a corresponding and gradual stretching of the definition of the agriculture and nature problem (although sometimes there was a considerable lag in relation to actual developments), new planning concepts were formed (particularly for nature and landscape conservation), an important widening of the policy areas and instruments involved took place, and policy coordination was strengthened. Policy did not really succeed in halting the degradation of nature, which was particularly advanced in sand areas. An important reason for this was that insufficient attention was paid to regional differentiation in agricultural development and, in particular, to the explosive development of intensive forms of agriculture in sand areas. The relationship between agriculture and drinking water recovery received attention late in spatial policy. Environmental and water policy and their instruments are primarily important in reversing the negative effects of agriculture on groundwater. Spatial policy can provide an important supportive function here.PART FOUR: RECONNAISSANCEWithin the framework of reconnaissance, an initial study was carried out into future trends within this dynamic agriculture. Also considered were developments expected to occur because of changes in market and price policy and in environmental policy. From this trend survey it appeared that future developments, in an agriculture actively reorientating itself, are surrounded by considerable uncertainty. Particularly because there is still a considerable amount of room within the boundary conditions set by market, price and environmental policy for agricultural development.The major spatial questions raised by agriculture development up to now, the possibility that existing spatial problems would become entrenched or extended, and the lack of an adequate guidance to agriculture from the perspective of spatial organization, have important implications for physical planning. These can be described as the working out of alternative directions for the development of spatial organization which can also function as indicators for agricultural development. These results are intended to provide material for social and political discussion on possible direction choices. The reconnaissance gives a nudge in this direction, as is shown below.Initially, given the analysis carried out earlier, this takes two parallel directions: one explores the future relationship between agriculture and spatial organization from the societal perspective, the other from the physical perspective. In the first instance, a development direction is worked out, intended to answer the problems of urban-agricultural congestion in the central zone on the one hand and of regional development in the peripheral zone on the other. If there is no guidance, both problems are likely to become more acute in the future Secondly, from the physical perspective, a development direction is devised to solve the problems in those extremely sensitive areas, heavily burdened by agriculture, whilst maintaining the spatial qualities of areas where the burden is, as yet, not so heavy. This development must also be seen in the perspective of an anticipated intensification in the problematic relationship between agriculture and spatial organization.The partial and one sided character of these two inquiries means that they conflict on a number of points. These are exactly the points that are crucial in working out linked development for agriculture and spatial organization. The deploying and integration of knowledge developed in the framework of both analysis and reconnaissance supports this elaboration. In this study three alternative directions are outlined and the North receives specific attention. The accent is on:1) reallocation of the (growth of) agricultural production capacity to the North to strengthen regional development;2) the North as an experimental area for a clean and integrated agriculture;3) reallocation of (the growth of) agricultural production capacity to the North, with the conservation of possibilities for nature conservation management and drink water recovery.These development directions are neither more nor less than exploratory directions supporting the discussion on a closer, linked development between agriculture and spatial organization in the Netherlands.</p

Sub-femtosecond electron bunches in laser wakefield acceleration via injection suppression with a magnetic field

It is shown that electron injection into a laser-driven plasma bubble can be manipulated by applying an external magnetic field in the presence of a plasma density gradient. The down-ramp of the density-tailored plasma locally reduces the plasma wave phase velocity, which triggers injection. The longitudinal magnetic field dynamically induces an expanding hole in the electron density distribution at the rear of the wake bubble, which reduces the peak electron velocity in its vicinity. Electron injection is suppressed when the electron velocity drops below the phase velocity, which depends on the size of the density hole. This enables the start and end of electron injection to be independently controlled, which allows generation of sub-femtosecond electron bunches with peak currents of a few kilo-Ampere, for an applied magnetic field of ∼ 10 Tesla

High quality electron beam acceleration by ionization injection in laser wakefields with mid-infrared dual-color lasers

For the laser wakefield acceleration, suppression of beam energy spread while keeping sufficient charge is one of the key challenges. In order to achieve this, we propose bichromatic laser ionization injection with combined laser wavelengths of 2.4 μ m and 0.8 μ m for wakefield excitation and triggering electron injection via field ionization, respectively. A laser pulse at 2.4 μ m wavelength enables one to drive an intense acceleration structure with a relatively low laser power. To further reduce the requirement of laser power, we also propose to use carbon dioxide as the working gas medium, where carbon acts as the injection element. Our three dimensional particle-in-cell simulations show that electron beams at the GeV energy level with both low energy spreads (around 1%) and high charges (several tens of picocoulomb) can be obtained by the use of this scheme with laser peak power totaling sub-100 TW

Plasma accelerator driven coherent spontaneous emission

Plasma accelerators [1] are a potentially important source of high energy, low emittance electron beams with high peak currents and generated within a relatively short distance. While novel plasma photocathodes [2] may offer improvement to the normalised emittance and brightness of electron beams compared to Radio Frequency-driven accelerators, a challenge is the energy spread and chirp of the beams, which can make FEL operation impossible. In this paper it is shown that such an energy-chirped beam, with a dynamically evolving current profile due to ballistic bunching, can generate significant coherent radiation output via the process of Coherent Spontaneous Emission (CSE) [3]. While this CSE is seen to cause some FEL-induced electron bunching at the radiation wavelength, the dynamic evolution of the energy chirped pulse dampens out any high-gain FEL interaction

Tunable Electron Multibunch Production in Plasma Wakefield Accelerators

Synchronized, independently tunable and focused $\mu$J-class laser pulses are used to release multiple electron populations via photo-ionization inside an electron-beam driven plasma wave. By varying the laser foci in the laboratory frame and the position of the underdense photocathodes in the co-moving frame, the delays between the produced bunches and their energies are adjusted. The resulting multibunches have ultra-high quality and brightness, allowing for hitherto impossible bunch configurations such as spatially overlapping bunch populations with strictly separated energies, which opens up a new regime for light sources such as free-electron-lasers

Ionization injection in a laser wakefield accelerator subject to a transverse magnetic field

The effect of an external transverse magnetic field on ionization injection of electrons in a laser wakefield accelerator (LWFA) is investigated by theoretical analysis and particle-in-cell simulations. On application of a few tens of Tesla magnetic field, both the electron trapping condition and the wakefield structure changes significantly such that injection occurs over a shorter distance and at an enhanced rate. Furthermore, beam loading is compensated for, as a result of the intrinsic trapezoidal-shaped longitudinal charge density profile of injected electrons. The nonlinear ionization injection and consequent compensation of beam loading lead to a reduction in the energy spread and an enhancement of both the charge and final peak energy of the electron beam from a LWFA immersed in the magnetic field

Eupraxia, a step toward a plasma-wakefield based accelerator with high beam quality

The EuPRAXIA project aims at designing the world's first accelerator based on advanced plasma-wakefield techniques to deliver 5 GeV electron beams that simultaneously have high charge, low emittance and low energy spread, which are required for applications by future user communities. Meeting this challenging objective will only be possible through dedicated effort. Many injection/acceleration schemes and techniques have been explored by means of thorough simulations in more than ten European research institutes. This enables selection of the most appropriate methods for solving each particular problem. The specific challenge of generating, extracting and transporting high charge beams, while maintaining the high quality needed for user applications, are being tackled using innovative approaches. This article highlights preliminary results obtained by the EuPRAXIA collaboration, which also exhibit the required laser and plasma parameters

Next-to-leading-order QCD Corrections to Higgs Production in association with a Jet

We compute the next-to-leading-order (NLO) QCD corrections to the Higgs pT distribution in Higgs production in association with a jet via gluon fusion at the LHC, with exact dependence on the mass of the quark circulating in the heavy-quark loops. The NLO corrections are presented including the top-quark mass, and for the first time, the bottom-quark mass as well. Further, besides the on-shell mass scheme, we consider for the first time a running mass renormalisation scheme. The computation is based on amplitudes which are valid for arbitrary heavy-quark masses.Comment: LaTeX, 7 pages, 5 figure

Plasma lensing of a laser wakefield accelerated electron bunch

We report on the first all-optical demonstration of plasma lensing using laser wakefield accelerated elec-trons in a two-stage setup. The LWFA electron bunch was focused by a second plasma stage without any ex-ternal fields applied..