Energy Compression and Stabilization of Laser-Plasma Accelerators.

Laser-plasma accelerators outperform current radio frequency technology in acceleration strength by orders of magnitude. Yet, enabling them to deliver competitive beam quality for demanding applications, particularly in terms of energy spread and stability, remains a major challenge. In this Letter, we propose to combine bunch decompression and active plasma dechirping for drastically improving the energy profile and stability of beams from laser-plasma accelerators. Realistic start-to-end simulations demonstrate the potential of these postacceleration phase-space manipulations for simultaneously reducing an initial energy spread and energy jitter of ∼1-2% to ≲0.1%, closing the beam-quality gap to conventional acceleration schemes.

Demonstration of a compact plasma accelerator powered by laser-accelerated electron beams.

Plasma wakefield accelerators are capable of sustaining gigavolt-per-centimeter accelerating fields, surpassing the electric breakdown threshold in state-of-the-art accelerator modules by 3-4 orders of magnitude. Beam-driven wakefields offer particularly attractive conditions for the generation and acceleration of high-quality beams. However, this scheme relies on kilometer-scale accelerators. Here, we report on the demonstration of a millimeter-scale plasma accelerator powered by laser-accelerated electron beams. We showcase the acceleration of electron beams to 128 MeV, consistent with simulations exhibiting accelerating gradients exceeding 100 GV m-1. This miniaturized accelerator is further explored by employing a controlled pair of drive and witness electron bunches, where a fraction of the driver energy is transferred to the accelerated witness through the plasma. Such a hybrid approach allows fundamental studies of beam-driven plasma accelerator concepts at widely accessible high-power laser facilities. It is anticipated to provide compact sources of energetic high-brightness electron beams for quality-demanding applications such as free-electron lasers.

Energy-Spread Preservation and High Efficiency in a Plasma-Wakefield Accelerator.

Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders. High efficiency and low energy spread can be achieved simultaneously by strong beam loading of plasma wakefields when accelerating bunches with carefully tailored current profiles [M. Tzoufras et al., Phys. Rev. Lett. 101, 145002 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.145002]. We experimentally demonstrate such optimal beam loading in a nonlinear electron-driven plasma accelerator. Bunches with an initial energy of 1 GeV were accelerated by 45 MeV with an energy-transfer efficiency of (42±4)% at a gradient of 1.3 GV/m while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level.

Compact Multistage Plasma-Based Accelerator Design for Correlated Energy Spread Compensation.

The extreme electromagnetic fields sustained by plasma-based accelerators could drastically reduce the size and cost of future accelerator facilities. However, they are also an inherent source of correlated energy spread in the produced beams, which severely limits the usability of these devices. We propose here to split the acceleration process into two plasma stages joined by a magnetic chicane in which the energy correlation induced in the first stage is inverted such that it can be naturally compensated in the second. Simulations of a particular 1.5-m-long setup show that 5.5 GeV beams with relative energy spreads of 1.2×10^{-3} (total) and 2.8×10^{-4} (slice) could be achieved while preserving a submicron emittance. This is at least one order of magnitude below the current state of the art and would enable applications such as compact free-electron lasers.

FLASHForward: plasma wakefield accelerator science for high-average-power applications.

The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Hybrid LWFA-PWFA staging as a beam energy and brightness transformer: conceptual design and simulations.

We present a conceptual design for a hybrid laser-driven plasma wakefield accelerator (LWFA) to beam-driven plasma wakefield accelerator (PWFA). In this set-up, the output beams from an LWFA stage are used as input beams of a new PWFA stage. In the PWFA stage, a new witness beam of largely increased quality can be produced and accelerated to higher energies. The feasibility and the potential of this concept is shown through exemplary particle-in-cell simulations. In addition, preliminary simulation results for a proof-of-concept experiment in Helmholtz-Zentrum Dresden-Rossendorf (Germany) are shown. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Intrinsic Stabilization of the Drive Beam in Plasma-Wakefield Accelerators.

The hose instability of the drive beam constitutes a major challenge for the stable operation of plasma-wakefield accelerators. In this Letter, we show that drive beams with a transverse size comparable to the plasma blowout radius generate a wake with a varying focusing along the beam, which leads to a rapid detuning of the slice-betatron oscillations and suppresses the instability. This intrinsic stabilization principle provides an applicable and effective method for the suppression of the hosing of the drive beam and allows for a stable acceleration process.

Observation of the Self-Modulation Instability via Time-Resolved Measurements.

Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximately 200 keV/c amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.

Chirp Mitigation of Plasma-Accelerated Beams by 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. Here, we propose to use a periodically modulated plasma density to shape the longitudinal fields acting on an electron bunch in the linear wakefield regime. With simulations, we demonstrate an on-average flat accelerating field that maintains a small beam energy spread.

Mitigation of the Hose Instability in Plasma-Wakefield Accelerators.

Current models predict the hose instability to crucially limit the applicability of plasma-wakefield accelerators. By developing an analytical model which incorporates the evolution of the hose instability over long propagation distances, this work demonstrates that the inherent drive-beam energy loss, along with an initial beam-energy spread, detunes the betatron oscillations of beam electrons and thereby mitigates the instability. It is also shown that tapered plasma profiles can strongly reduce initial hosing seeds. Hence, we demonstrate that the propagation of a drive beam can be stabilized over long propagation distances, paving the way for the acceleration of high-quality electron beams in plasma-wakefield accelerators. We find excellent agreement between our models and particle-in-cell simulations.

Litio para el tratamiento de la esclerosis lateral amiotrófica: mucho ruido para nada / Lithium for treatment of amyotrophic lateral sclerosis: much ado about nothing

Introducción: El litio fue propuesto en 2008 como un candidato eficaz en el tratamiento de ELA tras reportarse que era capaz de retrasar el deterioro funcional en un 40% y que ninguno de los 16 pacientes tratados con una combinación de litio más riluzole falleció durante un periodo de seguimiento de 15 meses. Los excelentes resultados de este estudio piloto despertaron una gran expectativa en pacientes, familiares, asociaciones de enfermos y comunidad científica. Consecuencia directa de esta noticia fue la puesta en marcha de numerosos ensayos clínicos en fase ii. Muchos de los pacientes, que no pudieron ser incluidos en estos estudios, utilizaron todos sus recursos para acceder a este fármaco mediante uso compasivo. Objetivos: Evaluar la eficacia del litio en ELA mediante un metaanálisis de la información reportada en 12 de estos estudios. Se analiza su calidad metodológica. Material y métodos: Se realizaron búsquedas en MEDLINE, EMBASE y Registros Cochrane del Grupo de Enfermedades Neuromusculares, ClinicalTrials.gov y EudraCT (enero de 1996-agosto de 2012). Resultados: Hasta la fecha disponemos de información de más de 1.100 pacientes tratados con litio. Lamentablemente los resultados obtenidos no confirman el efecto positivo descrito en el estudio piloto y sugieren que este fármaco es ineficaz para detener la progresión de la enfermedad. Dos ensayos tuvieron que ser suspendidos antes del plazo previsto por ineficacia del fármaco y por numerosos efectos adversos. En un estudio publicado recientemente se descarta también cualquier posibilidad de un mínimo efecto. Conclusiones: Hay evidencia de que el litio no ofrece beneficios a corto plazo en ELA. Al comparar el grupo de pacientes tratados con litio + riluzole con el grupo control tratado con riluzole no se observan diferencias estadísticamente significativas en las tasas de deterioro funcional o de deterioro de la función respiratoria ni tampoco en la supervivencia. No hay tampoco evidencia de que sea superior al placebo

Introduction: Lithium was proposed in 2008 as an effective candidate in the treatment of ALS after a report claimed that it was able to delay functional deterioration by 40% and that none of the 16 patients treated with a combination of lithium plus riluzole had died during a 15-month follow-up period. The excellent results of this pilot study engendered considerable optimism among patients, their families, patients’ associations, and the scientific community. This report sparked numerous phase ii clinical trials. Many patients who were not included in these studies used all resources at their disposal to access the drug as treatment under a compassionate use programme. Objectives: To evaluate the effectiveness of lithium in ALS using a meta-analysis of the information reported in 12 studies which were examined for methodological quality. Material and methods: Searches were performed using MEDLINE, EMBASE, the Cochrane Neuromuscular Disease Group Trials Register, ClinicalTrials.gov, and EudraCT (January 1996-August 2012). Results: To date, we have information on more 1100 patients treated with lithium. Unfortunately, the results do not confirm the positive effect described in the pilot study, which suggests that this drug is not effective at slowing disease progression. Two trials had to be suspended before the scheduled completion date due to the ineffectiveness of the drug as well as numerous adverse effects. A recently published study also ruled out any possible modest effect. Conclusions: There is evidence to suggest that lithium has no short-term benefits in ALS. A comparison of the group of patients treated with lithium + riluzole and the control group treated with riluzole alone showed no statistically significant differences in rates of functional decline, deterioration of respiratory function, or survival time. Furthermore, there was no evidence that it was more effective than the placebo

Lithium for treatment of amyotrophic lateral sclerosis: much ado about nothing. / Litio para el tratamiento de la esclerosis lateral amiotrófica: mucho ruido para nada.

INTRODUCTION: Lithium was proposed in 2008 as an effective candidate in the treatment of ALS after a report claimed that it was able to delay functional deterioration by 40% and that none of the 16 patients treated with a combination of lithium plus riluzole had died during a 15-month follow-up period. The excellent results of this pilot study engendered considerable optimism among patients, their families, patients' associations, and the scientific community. This report sparked numerous phase ii clinical trials. Many patients who were not included in these studies used all resources at their disposal to access the drug as treatment under a compassionate use programme. OBJECTIVES: To evaluate the effectiveness of lithium in ALS using a meta-analysis of the information reported in 12 studies which were examined for methodological quality. MATERIAL AND METHODS: . Searches were performed using MEDLINE, EMBASE, the Cochrane Neuromuscular Disease Group Trials Register, ClinicalTrials.gov, and EudraCT (January 1996-August 2012). RESULTS: To date, we have information on more 1100 patients treated with lithium. Unfortunately, the results do not confirm the positive effect described in the pilot study, which suggests that this drug is not effective at slowing disease progression. Two trials had to be suspended before the scheduled completion date due to the ineffectiveness of the drug as well as numerous adverse effects. A recently published study also ruled out any possible modest effect. CONCLUSIONS: There is evidence to suggest that lithium has no short-term benefits in ALS. A comparison of the group of patients treated with lithium+riluzole and the control group treated with riluzole alone showed no statistically significant differences in rates of functional decline, deterioration of respiratory function, or survival time. Furthermore, there was no evidence that it was more effective than the placebo.

High-quality electron beams from beam-driven plasma accelerators by wakefield-induced ionization injection.

We propose a new and simple strategy for controlled ionization-induced trapping of electrons in a beam-driven plasma accelerator. The presented method directly exploits electric wakefields to ionize electrons from a dopant gas and capture them into a well-defined volume of the accelerating and focusing wake phase, leading to high-quality witness bunches. This injection principle is explained by example of three-dimensional particle-in-cell calculations using the code OSIRIS. In these simulations a high-current-density electron-beam driver excites plasma waves in the blowout regime inside a fully ionized hydrogen plasma of density 5×10(17)cm-3. Within an embedded 100 µm long plasma column contaminated with neutral helium gas, the wakefields trigger ionization, trapping of a defined fraction of the released electrons, and subsequent acceleration. The hereby generated electron beam features a 1.5 kA peak current, 1.5 µm transverse normalized emittance, an uncorrelated energy spread of 0.3% on a GeV-energy scale, and few femtosecond bunch length.