460 research outputs found
Wakefield-Induced Ionization injection in beam-driven plasma accelerators
We present a detailed analysis of the features and capabilities of
Wakefield-Induced Ionization (WII) injection in the blowout regime of beam
driven plasma accelerators. This mechanism exploits the electric wakefields to
ionize electrons from a dopant gas and trap them in a well-defined region of
the accelerating and focusing wake phase, leading to the formation of
high-quality witness-bunches [Martinez de la Ossa et al., Phys. Rev. Lett. 111,
245003 (2013)]. The electron-beam drivers must feature high-peak currents
() and a duration comparable to the plasma
wavelength to excite plasma waves in the blowout regime and enable WII
injection. In this regime, the disparity of the magnitude of the electric field
in the driver region and the electric field in the rear of the ion cavity
allows for the selective ionization and subsequent trapping from a narrow phase
interval. The witness bunches generated in this manner feature a short duration
and small values of the normalized transverse emittance (). In addition, we show that the amount of injected
charge can be adjusted by tuning the concentration of the dopant gas species,
which allows for controlled beam loading and leads to a reduction of the total
energy spread of the witness beams. Electron bunches, produced in this way,
fulfil the requirements to drive blowout regime plasma wakes at a higher
density and to trigger WII injection in a second stage. This suggests a
promising new concept of self-similar staging of WII injection in steps with
increasing plasma density, giving rise to the potential of producing electron
beams with unprecedented energy and brilliance from plasma-wakefield
accelerators
Actividades y estrategias para hacerse a los medios de vida de una familia en el área rural de la depresión momposina, colombia
The means of life of a family of the rural area of the Momposina depression region, Colombia were analyzed. It was found that inside the assets, the social, natural and human capital, they give the sustainability, while the physical capital and financier are those that present bigger weakness that which does not allow concluding that sustainable exists to complete the objectives as regards means of life. It is evidenced that the integration among the different variables that compose the means of life should be related in a positive way to reach the sustainable.Se analizan los medios de vida de una familia del área rural de la depresión momposina, Colombia. Se encontró que dentro de los activos, el capital social, natural y humano, dan la sustentabilidad, mientras que el capital fÃsico y financiero son los que presentan mayor debilidad, lo cual no permite concluir que exista sostenibilidad para cumplir los objetivos en materia de medios de vida. Se evidencia que la integración entre las diferentes variables que componen los medios de vida se relacionan de forma positiva para alcanzar la sostenibilidad
ArgoNeuT, a liquid argon time projection chamber in a low energy neutrino beam
ArgoNeuT (Argon Neutrino Test), a NSF/DOE project at Fermilab, is the first
LArTPC to go in a low energy neutrino beam and just the second LArTPC to go in
a neutrino beam ever. ArgoNeuT sits just upstream of the on-axis MINOS near
detector in the NuMI beamline, about 1 km from the target station and 100 m
underground. The detector features a 47X40X90 cm (169 L) active volume TPC with
a fully contained recirculation and purification system. Among other physics,
ArgoNeuT will measure the charged-current quasi-elastic (anti-) neutrino cross
section on argon at an energy of ~3 GeV.Comment: 3 pages, 2 figures, to appear in the proceedings of the 11th
International Conference on Topics in Astroparticle and Underground Physics
(TAUP 2009), Rome, Italy, 1-5 July 200
Toric Calabi-Yau Fourfolds, Duality Between N=1 Theories and Divisors that Contribute to the Superpotential
We study issues related to F-theory on Calabi-Yau fourfolds and its duality to heterotic theory for Calabi-Yau threefolds. We discuss principally fourfolds that are described by reflexive polyhedra and show how to read off some of the data for the heterotic theory from the polyhedron. We give a procedure for constructing examples with given gauge groups and describe some of these examples in detail. Interesting features arise when the local pieces are fitted into a global manifold. An important issue is how to compute the superpotential explicitly. Witten has shown that the condition for a divisor to contribute to the superpotential is that it have arithmetic genus 1. Divisors associated with the short roots of non-simply laced gauge groups do not always satisfy this condition while the divisors associated to all other roots do. For such a `dissident' divisor we distinguish cases for which the arithmetic genus is greater than unity corresponding to an X that is not general in moduli (in the toric case this corresponds to the existence of non-toric parameters). In these cases the `dissident' divisor D does not remain an effective divisor for general complex structure. If however the arithmetic genus is less than or equal to 0, then the divisor is general in moduli and there is a genuine instability
Optimización del proceso de extracción de tocoferol de germen de trigo con dióxido de carbono lÃquido y supercrÃtico.
In this work the extraction of tocopherol from wheat germ by liquid and supercritical carbon dioxide has been studied. It has been analysed the operative conditions as well as the row material pre-treatment. At the optimum operating conditions, the yield of supercritical extraction is similar to the conventional extraction by hexano as solvent. So, this technique can be competitive respect of the conventional technique because the solvent removal by distillation is not necessary.En el presente trabajo se estudia la extracción de tocoferol a partir de germen de trigo utilizando dióxido de carbono lÃquido y supercrÃtico como disolvente. Las variables que intervienen en la extracción se han analizado tanto desde el punto de vista operativo como de adecuación de la materia prima. Los rendimientos obtenidos son muy similares a los encontrados en la extracción convencional utilizando hexano. Esta técnica, portante, puede resultar competitiva respecto a la convencional, ya que se evita tener que destilar el extracto para eliminar el disolvente
ArgoNeuT and the Neutrino-Argon Charged Current Quasi-Elastic Cross Section
ArgoNeuT, a Liquid Argon Time Projection Chamber in the NuMI beamline at
Fermilab, has recently collected thousands of neutrino and anti-neutrino events
between 0.1 and 10 GeV. The experiment will, among other things, measure the
cross section of the neutrino and anti-neutrino Charged Current Quasi-Elastic
interaction and analyze the vertex activity associated with such events. These
topics are discussed along with ArgoNeuT's automated reconstruction software,
currently capable of fully reconstructing the muon and finding the event vertex
in neutrino interactions.Comment: 6 pages, 4 figures, presented at the International Nuclear Physics
Conference, Vancouver, Canada, July 4-9, 2010, to be published in Journal of
Physics: Conference Series (JPCS
Chirp mitigation of plasma-accelerated beams using a modulated plasma density
Plasma-based accelerators offer the possibility to drive future compact light
sources and high-energy physics applications. Achieving good beam quality,
especially a small beam energy spread, is still one of the major challenges.
For stable transport, the beam is located in the focusing region of the
wakefield which covers only the slope of the accelerating field. This, however,
imprints a longitudinal energy correlation (chirp) along the bunch. Here, we
propose an alternating focusing scheme in the plasma to mitigate the
development of this chirp and thus maintain a small energy spread
Bayesian optimization of laser-plasma accelerators assisted by reduced physical models
Particle-in-cell simulations are among the most essential tools for the
modeling and optimization of laser-plasma accelerators, since they reproduce
the physics from first principles. However, the high computational cost
associated with them can severely limit the scope of parameter and design
optimization studies. Here, we show that a multitask Bayesian optimization
algorithm can be used to mitigate the need for such high-fidelity simulations
by incorporating information from inexpensive evaluations of reduced physical
models. In a proof-of-principle study, where a high-fidelity optimization with
FBPIC is assisted by reduced-model simulations with Wake-T, the algorithm
demonstrates an order-of-magnitude speedup. This opens a path for the
cost-effective optimization of laser-plasma accelerators in large parameter
spaces, an important step towards fulfilling the high beam quality requirements
of future applications
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