Ion motion in the wake driven by long particle bunches in plasmas

We explore the role of the background plasma ion motion in self-modulated plasma wakefield accelerators. We employ J. Dawson's plasma sheet model to derive expressions for the transverse plasma electric field and ponderomotive force in the narrow bunch limit. We use these results to determine the on-set of the ion dynamics, and demonstrate that the ion motion could occur in self-modulated plasma wakefield accelerators. Simulations show the motion of the plasma ions can lead to the early suppression of the self-modulation instability and of the accelerating fields. The background plasma ion motion can nevertheless be fully mitigated by using plasmas with heavier plasmas.Comment: 23 pages, 6 figure

Conditions for the onset of the current filamentation instability in the laboratory

Current Filamentation Instability (CFI) is capable of generating strong magnetic fields relevant to explain radiation processes in astrophysical objects and lead to the onset of particle acceleration in collisionless shocks. Probing such extreme scenarios in the laboratory is still an open challenge. In this work, we investigate the possibility of using neutral $e^{-}$ $e^{+}$ beams to explore the CFI with realistic parameters, by performing 2D particle-in-cell simulations. We show that CFI can occur unless the rate at which the beam expands due to finite beam emittance is larger than the CFI growth rate and as long as the role of competing electrostatic two-stream instability (TSI) is negligible. We also show that the longitudinal energy spread, typical of plasma based accelerated electron-positron fireball beams, plays a minor role in the growth of CFI in these scenarios

All-optical trapping and acceleration of heavy particles

A scheme for fast, compact, and controllable acceleration of heavy particles in vacuum is proposed, in which two counterpropagating lasers with variable frequencies drive a beat-wave structure with variable phase velocity, thus allowing for trapping and acceleration of heavy particles, such as ions or muons. Fine control over the energy distribution and the total charge of the beam is obtained via tuning of the frequency variation. The acceleration scheme is described with a one-dimensional theory, providing the general conditions for trapping and scaling laws for the relevant features of the particle beam. Two-dimensional, electromagnetic particle-in-cell simulations confirm the validity and the robustness of the physical mechanism.Comment: 10 pages, 3 figures, to appear in New Journal of Physic

Modelling radiation emission in the transition from the classical to the quantum regime

An emissivity formula is derived using the generalised Fermi-Weizacker-Williams method of virtual photons which accounts for the recoil the charged particle experiences as it emits radiation. It is found that through this derivation the formula obtained by Sokolov et al using QED perturbation theory is recovered. The corrected emissivity formula is applied to nonlinear Thomson scattering scenarios in the transition from the classical to the quantum regime, for small values of the nonlinear quantum parameter \chi. Good agreement is found between this method and a QED probabilistic approach for scenarios where both are valid. In addition, signatures of the quantum corrections are identified and explored.Comment: 11 pages, 4 figures, submitted for publicatio

Relações espaciais entre fertilidade do solo e produtividade de culturas sob sistema de plantio direto.

O objetivo deste trabalho foi analisar a variabilidade espacial de atributos de fertilidade do solo e sua influência na produtividade de culturas sob o sistema de plantio direto. o experimento está localizado no Centro Experimental Central do Instituto Agronômico, Campinas, SP, onde foram determinados os dados de produtividade (kg ha -1) das safras de labelabe, milho, triticale e mamona e dados de fertilidade do solo na profundidade de 0,0-0,20 m. A estatística descritiva foi utilizada para avaliar a variabilidade espacial. Todas as variáveis apresentaram dependência espacial e tiverem seus semivariogramas ajustados ao modelo esférico. Os mapas construídos com valores interpolados por krigagem indicam que a parte lateral esquerda da área apresentou a maior relação espacial entre produtividade e os atributos de fertilidade do solo, favorecendo o manejo diferenciado na área

Variabilidade espacial e temporal dos mapas de colheita e dos atributos químicos do solo em Votuporanga, SP.

A variabilidade das produtividades das culturas tende a acompanhar a do solo, por isso, torna-se necessário conhecer a relação espacial entre elas. O objetivo foi avaliar e comparar a variabilidade espacial de dados de colheita entre 1994 a 1998 com os atributos químicos do solo da área sob plantio direto em Votuporanga, SP. A área de cerca de 1 ha, foi amostrada numa grade de 10 x 10 m (110 pontos), em um Latossolo Vermelho de textura média. Foram amostradas as seguintes culturas: soja em 1994, arroz em 1995, soja em 1995, milho em 1995, algodão em 1997, aveia preta em 1997 e milho em 1998. As produtividades das culturas foram obtidas e normalizadas possibilitando a comparação das produtividades entre as diferentes culturas. O solo foi amostrado de 0-10 e de 10-20 cm de profundidade para análise química. Houve relação espacial direta entre as produtividades das culturas e o pH KCl e cálcio nas duas profundidades, indicando que podem ser definidas zonas de manejo diferenciado para correção de acidez do solo em função da melhoria da produtividade das culturas na área

The ion motion in self-modulated plasma wakefield accelerators

The effects of plasma ion motion in self-modulated plasma based accelerators is examined. An analytical model describing ion motion in the narrow beam limit is developed, and confirmed through multi-dimensional particle-in-cell simulations. It is shown that the ion motion can lead to the early saturation of the self-modulation instability, and to the suppression of the accelerating gradients. This can reduce the total energy that can be transformed into kinetic energy of accelerated particles. For the parameters of future proton-driven plasma accelerator experiments, the ion dynamics can have a strong impact. Possible methods to mitigate the effects of the ion motion in future experiments are demonstrated.Comment: 11 pages, 3 figures, accepted for publication in Phys. Rev. Let