We present a study on the emittance evolution of electron bunches, externally injected into laser-driven plasma waves using the three-dimensional particle-in-cell (PIC) code OSIRIS. Results show ...order-of-magnitude transverse emittance growth during the injection process, if the electron bunch is not matched to its intrinsic betatron motion inside the wakefield. This behavior is supported by analytic theory reproducing the simulation data to a percent level. The length over which the full emittance growth develops is found to be less than or comparable to the typical dimension of a single plasma module in current multistage designs. In addition, the analytic theory enables the quantitative prediction of emittance degradation in two consecutive accelerators coupled by free-drift sections, excluding this as a scheme for effective emittance-growth suppression, and thus suggests the necessity of beam-matching sections between acceleration stages with fundamental implications on the overall design of staged laser-wakefield accelerators.
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.
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.
We present simulations of injection of plasma electrons triggered by a negative gradient in the plasma-density profile for beam-driven plasma-wakefield acceleration. Studies show the potential of ...this trapping technique for the production of narrow-energy bandwidth, femtosecond, high-current electron beams with a small transverse normalised emittance in the hundred nm range. Moreover, the accelerated beams feature strong longitudinal phase-space correlations with sub-percent uncorrelated energy spreads. Tuning of density down-ramp injection is explored by scanning the slope and length of the downward transition. It is found that the mechanism causes particle trapping over a wide experimentally accessible parameter range. All simulations were performed in three spatial dimensions with the particle-in-cell code OSIRIS 1. The investigated driver-beam properties and the plasma profile resemble expected experimental conditions at the FLASHForward facility at DESY.
Abstract Purpose To describe the frequency of glenoid chondral abnormalities in relation to Hill Sachs (HS) lesions in MR arthrograms of patients with anterior shoulder instability versus controls. ...Such glenoid lesions can directly impact surgical decision-making and approach, and potentially negatively impact outcome if missed. Materials and methods Retrospective analysis of direct MR shoulder arthrograms in 165 subjects, (101 with anterior instability/64 controls) was performed independently by 2 blinded musculoskeletal radiologists. Outcome measures were the presence of a HS, anterior labral pathology and glenoid chondral injury. Kappa statistic, Pearson Chi-square and Mann–Whitney analysis were employed for analysis. Results Inter-observer variability for the presence of HS, labral and chondral lesions was 0.964, 0.965 and 0.858 respectively, with intra-observer variability of 1.0, 0.985 and 0.861 for the principle reader. 58% of patients and 8% of controls had HS ( p < 0.001). 72% of patients and 25% of controls had anterior labral injury ( p < 0.001). 36% of instability patients and 10% controls had glenoid chondral lesions ( p < 0.001). 46% of anterior instability patients with HS defects had chondral injury as opposed to 21% of patients without HS defects ( p = 0.009). Depth of the HS lesion did not increase the likelihood of a glenoid chondral lesion ( p = 0.7335). Conclusion In the clinical anterior instability cohort, we demonstrated a statistically significant higher number of HS and glenoid chondral lesions than in controls. In anterior instability patients, the presence of a HS lesion confers a statistically significant greater likelihood of having a glenoid chondral lesion when compared to patients with instability and no HS.
We use three-dimensional (3D) simulations with the particle-in-cell (PIC) code OSIRIS to demonstrate the theoretical production of high-quality electron bunches in beam-driven plasma wakefield ...accelerators (PWFA) by means of field-induced ionization injection. In these simulations, two realistic scenarios for PWFA have been considered: the FLASHForward project at DESY and the FACET experiment at SLAC. These two examples illustrate two different strategies for injection. The first one uses the transverse electric fields of the beam to induce injection, and the second constitutes a new method which utilizes only the wakefields to enable ionization and trapping of high quality electron bunches into beam driven plasma wakes. The produced bunches feature multi-kA peak currents, ~1μm transverse normalized emittances, uncorrelated energy spreads of ≤1% on a GeV-energy scale, and few femtosecond bunch lengths.
The FLASHForward facility at DESY Aschikhin, A.; Behrens, C.; Bohlen, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2016, Volume:
806
Journal Article
Peer reviewed
Open access
The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of ...quality sufficient to be used in a free-electron laser. The plasma is created by ionising a gas in a gas cell with a multi-TW laser system. The plasma wave will be driven by high-current-density electron beams from the FLASH linear accelerator. The laser system can also be used to provide optical diagnostics of the plasma and electron beams due to the <30fs synchronisation between the laser and the driving electron beam. The project will explore both external and internal witness-beam injection techniques. The operation parameters of the experiment are discussed, as well as the scientific programme.
Introduction: Hearing preservation is invariably a consideration when exploring treatment options for acoustic neuromas. We reviewed the long‐term hearing results of patients who were treated using ...1) hyperfractionated stereotactic radiotherapy (HSR), 2) hearing preservation tumor excision surgery (HPTES), and 3) expectantly (no treatment).
Methods and Materials: Single institution retrospective chart review of 42 patients managed with HSR (1993–2003), 113 patients in whom HPTES was carried out, and 86 patients who were untreated (1974–2003). Hearing levels were graded according to the Gardner‐Robertson classification.
Results: The percent of patients managed with HSR initially who had serviceable hearing (class 1–2) was 68.8%. This fell to 6.7% in the follow‐up interval. Of the group treated with HPTES, 100% had preoperative serviceable hearing. This dropped to 15.9% in the follow‐up interval. The percent of patients managed expectantly who initially had serviceable hearing was 77.3%. This dropped to 33.3% during the follow‐up interval. Mean follow‐up periods were 4.0, 9.5, and 6.8 years in the HSR, HPTES, and expectant groups, respectively.
Conclusions: Hearing acuity statistically worsened over the long term (P < .01) in all three groups. There was a significant proportion of patients in whom hearing deteriorated from serviceable to nonserviceable hearing (P < .01) during the follow‐up interval. The decline was most significant in the groups treated with HPTES and HSR compared with the group treated expectantly (P < .05). Hearing outcomes, in our experience, continue to be poor, but this is especially so in patients treated with HPTES or HSR.
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 (PIC) calculations using the code OSIRIS. In these simulations a high-current-density electron-beam driver excites plasma waves in the blow-out regime inside a fully-ionized hydrogen plasma of density \(5\times10^{17} \mathrm{cm^{-3}}\). Within an embedded \(100 \mathrm{\mu m}\) 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 \(1.5 \mathrm{kA}\) peak current, \(1.5 \mathrm{\mu m}\) transverse normalized emittance, an uncorrelated energy spread of 0.3% on a GeV-energy scale, and few femtosecond bunch length.
PDF
