| 1. |
- Walker, Anthony P, et al.
(författare)
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Horizon 2020 EuPRAXIA design study
- 2017
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 874:1
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Tidskriftsartikel (refereegranskat)abstract
- The Horizon 2020 Project EuPRAXIA ("European Plasma Research Accelerator with eXcellence In Applications") is preparing a conceptual design report of a highly compact and cost-effective European facility with multi-GeV electron beams using plasma as the acceleration medium. The accelerator facility will be based on a laser and/or a beam driven plasma acceleration approach and will be used for photon science, high-energy physics (HEP) detector tests, and other applications such as compact X-ray sources for medical imaging or material processing. EuPRAXIA started in November 2015 and will deliver the design report in October 2019. EuPRAXIA aims to be included on the ESFRI roadmap in 2020.
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| 2. |
- Behm, K. T., et al.
(författare)
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A spectrometer for ultrashort gamma-ray pulses with photon energies greater than 10 MeV
- 2018
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 89:11
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Author(s). We present a design for a pixelated scintillator based gamma-ray spectrometer for non-linear inverse Compton scattering experiments. By colliding a laser wakefield accelerated electron beam with a tightly focused, intense laser pulse, gamma-ray photons up to 100 MeV energies and with few femtosecond duration may be produced. To measure the energy spectrum and angular distribution, a 33 × 47 array of cesium-iodide crystals was oriented such that the 47 crystal length axis was parallel to the gamma-ray beam and the 33 crystal length axis was oriented in the vertical direction. Using an iterative deconvolution method similar to the YOGI code, modeling of the scintillator response using GEANT4 and fitting to a quantum Monte Carlo calculated photon spectrum, we are able to extract the gamma ray spectra generated by the inverse Compton interaction.
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| 3. |
- Cole, J. M., et al.
(författare)
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Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam
- 2018
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Ingår i: Physical Review X. - 2160-3308. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration (μ 500 MeV) with an intense laser pulse (a0 > 10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy > 30 MeV.
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| 4. |
- Hussein, A. E., et al.
(författare)
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Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 μm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from laser wakefield acceleration can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures.
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| 5. |
- Maitrallain, A., et al.
(författare)
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Parametric study of high-energy ring-shaped electron beams from a laser wakefield accelerator
- 2022
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- Laser wakefield accelerators commonly produce on-axis, low-divergence, high-energy electron beams. However, a high charge, annular shaped beam can be trapped outside the bubble and accelerated to high energies. Here we present a parametric study on the production of low-energy-spread, ultra-relativistic electron ring beams in a two-stage gas cell. Ring-shaped beams with energies higher than 750 MeV are observed simultaneously with on axis, continuously injected electrons. Often multiple ring shaped beams with different energies are produced and parametric studies to control the generation and properties of these structures were conducted. Particle tracking and particle-in-cell simulations are used to determine properties of these beams and investigate how they are formed and trapped outside the bubble by the wake produced by on-axis injected electrons. These unusual femtosecond duration, high-charge, high-energy, ring electron beams may find use in beam driven plasma wakefield accelerators and radiation sources.
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| 6. |
- Spesyvtsev, R., et al.
(författare)
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Generation of electron high energy beams with a ring-like structure by a dual stage laser wakefield accelerator
- 2019
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Ingår i: Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III. - : SPIE. - 9781510627383 ; 11036
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Konferensbidrag (refereegranskat)abstract
- The laser wake-field accelerator (LWFA) traditionally produces high brightness, quasi-monoenergetic electron beams with Gaussian-like spatial and angular distributions. In the present work we investigate the generation of ultra-relativistic beams with ring-like structures in the blowout regime of the LWFA using a dual stage accelerator. A density down-ramp triggers injection after the first stage and is used to produce ring-like electron spectra in the 300 - 600 MeV energy range. These well defined, annular beams are observed simultaneously with the on-axis, high energy electron beams, with a divergence of a few milliradians. The rings have quasi-monoenergetic energy spectra with an RMS spread estimated to be less than 5%. Particle-in-cell simulations confirm that off-axis injection provides the electrons with the initial transverse momentum necessary to undertake distinct betatron oscillations within the plasma bubble during their acceleration process.
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| 7. |
- Streeter, M. J.V., et al.
(författare)
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Characterization of laser wakefield acceleration efficiency with octave spanning near-IR spectrum measurements
- 2022
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Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 25:10
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Tidskriftsartikel (refereegranskat)abstract
- We report on experimental measurements of energy transfer efficiencies in a GeV-class laser wakefield accelerator. Both the transfer of energy from the laser to the plasma wakefield and from the plasma to the accelerated electron beam was diagnosed by simultaneous measurement of the deceleration of laser photons and the acceleration of electrons as a function of plasma length. The extraction efficiency, which we define as the ratio of the energy gained by the electron beam to the energy lost by the self-guided laser mode, was maximized at 19±3% by tuning the plasma density and length. The additional information provided by the octave-spanning laser spectrum measurement allows for independent optimization of the plasma efficiency terms, which is required for the key goal of improving the overall efficiency of laser wakefield accelerators.
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| 8. |
- Warwick, J., et al.
(författare)
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Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam
- 2017
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 119:18
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (amp;gt;= 1 T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of epsilon(B) approximate to 10(-3) is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.
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| 9. |
- Kettle, B., et al.
(författare)
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Single-Shot Multi-keV X-Ray Absorption Spectroscopy Using an Ultrashort Laser-Wakefield Accelerator Source
- 2019
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Ingår i: Physical Review Letters. - 0031-9007. ; 123:25
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Tidskriftsartikel (refereegranskat)abstract
- Single-shot absorption measurements have been performed using the multi-keV x rays generated by a laser-wakefield accelerator. A 200 TW laser was used to drive a laser-wakefield accelerator in a mode which produced broadband electron beams with a maximum energy above 1 GeV and a broad divergence of ≈15 mrad FWHM. Betatron oscillations of these electrons generated 1.2±0.2×106 photons/eV in the 5 keV region, with a signal-to-noise ratio of approximately 300 1. This was sufficient to allow high-resolution x-ray absorption near-edge structure measurements at the K edge of a titanium sample in a single shot. We demonstrate that this source is capable of single-shot, simultaneous measurements of both the electron and ion distributions in matter heated to eV temperatures by comparison with density functional theory simulations. The unique combination of a high-flux, large bandwidth, few femtosecond duration x-ray pulse synchronized to a high-power laser will enable key advances in the study of ultrafast energetic processes such as electron-ion equilibration.
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| 10. |
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| 11. |
- Wilkie, F. L., et al.
(författare)
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Cognitive functioning in younger and older HIV-1 - Infected adults
- 2003
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Ingår i: Journal of Acquired Immune Deficiency Syndromes. - : Wolters Kluwer. - 1525-4135 .- 1944-7884. ; 33, s. S93-S105
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Tidskriftsartikel (refereegranskat)abstract
- In young adults, a major neurologic complication of HIV-1 infection is cognitive motor impairment. Epidemiologic findings suggest that increasing age is a significant risk factor for HIV-1-associated dementia as the AIDS-defining illness. Findings from the few studies that have directly measured cognition in younger and older HIV-1-infected adults, however, have been mixed, in pan, because of small sample sizes and other methodologic differences between studies. The authors present preliminary findings on cognitive functioning in symptomatic HIV-1-infected younger (aged 20-39 years) and older (aged 50 years or older) adults. Independent of age, HIV-1 infection was accompanied by learning and memory retrieval deficits, which were significantly associated with high plasma viral loads in the young adults. Relative to the younger and older HIV-1-negative (HIV-1-) groups, only the younger HIV-1-positive (HIV-1(+))group had significantly longer reaction times (RTs). Within the older HIV-1(+) group, however, longer simple and choice RTs were significantly correlated with higher viral loads and lower CD4 cell counts. Although HIV-1 infection affects cognition independent of age, longitudinal studies involving large numbers of older individuals are needed to determine whether there are age differences in the prevalence, nature, and severity of HIV-1-associated cognitive dysfunction.
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| 12. |
- Österblom, Henrik, et al.
(författare)
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Incentives, social-ecological feedbacks and European fisheries
- 2011
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Ingår i: Marine Policy. - : Elsevier BV. - 0308-597X .- 1872-9460. ; 35:5, s. 568-574
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Tidskriftsartikel (refereegranskat)abstract
- The European Common Fisheries Policy (CFP) has failed to deliver on social, economic and ecological goals. This failure is in part the result of a number of social-ecological feedback mechanisms. The policy is currently undergoing reform, with unknown practical outcomes. Here, relatively successful fisheries policies outside the European Union are reviewed. Through interviews and workshops with scientists, managers and other stakeholders, complemented with literature reviews, practices that can create incentives for long-term sustainability are investigated. The focus is on how the provision of clear and trusted scientific evidence can stimulate defensible decisions, in turn creating incentives for compliance, leading to positive social-ecological outcomes. Despite differences between Europe and the investigated case studies, the prospects of an increased regionalization within the European CFP provides the best starting point for implementing best practice identified in this study.
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