1. |
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2. |
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3. |
- Bravo, L, et al.
(author)
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- 2021
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swepub:Mat__t
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4. |
- Tabiri, S, et al.
(author)
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- 2021
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swepub:Mat__t
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5. |
- Glasbey, JC, et al.
(author)
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- 2021
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swepub:Mat__t
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6. |
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7. |
- Khatri, C, et al.
(author)
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Outcomes after perioperative SARS-CoV-2 infection in patients with proximal femoral fractures: an international cohort study
- 2021
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In: BMJ open. - : BMJ. - 2044-6055. ; 11:11, s. e050830-
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Journal article (peer-reviewed)abstract
- Studies have demonstrated high rates of mortality in people with proximal femoral fracture and SARS-CoV-2, but there is limited published data on the factors that influence mortality for clinicians to make informed treatment decisions. This study aims to report the 30-day mortality associated with perioperative infection of patients undergoing surgery for proximal femoral fractures and to examine the factors that influence mortality in a multivariate analysis.SettingProspective, international, multicentre, observational cohort study.ParticipantsPatients undergoing any operation for a proximal femoral fracture from 1 February to 30 April 2020 and with perioperative SARS-CoV-2 infection (either 7 days prior or 30-day postoperative).Primary outcome30-day mortality. Multivariate modelling was performed to identify factors associated with 30-day mortality.ResultsThis study reports included 1063 patients from 174 hospitals in 19 countries. Overall 30-day mortality was 29.4% (313/1063). In an adjusted model, 30-day mortality was associated with male gender (OR 2.29, 95% CI 1.68 to 3.13, p<0.001), age >80 years (OR 1.60, 95% CI 1.1 to 2.31, p=0.013), preoperative diagnosis of dementia (OR 1.57, 95% CI 1.15 to 2.16, p=0.005), kidney disease (OR 1.73, 95% CI 1.18 to 2.55, p=0.005) and congestive heart failure (OR 1.62, 95% CI 1.06 to 2.48, p=0.025). Mortality at 30 days was lower in patients with a preoperative diagnosis of SARS-CoV-2 (OR 0.6, 95% CI 0.6 (0.42 to 0.85), p=0.004). There was no difference in mortality in patients with an increase to delay in surgery (p=0.220) or type of anaesthetic given (p=0.787).ConclusionsPatients undergoing surgery for a proximal femoral fracture with a perioperative infection of SARS-CoV-2 have a high rate of mortality. This study would support the need for providing these patients with individualised medical and anaesthetic care, including medical optimisation before theatre. Careful preoperative counselling is needed for those with a proximal femoral fracture and SARS-CoV-2, especially those in the highest risk groups.Trial registration numberNCT04323644
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8. |
- de Graauw, Th., et al.
(author)
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The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
- 2010
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L6-
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Journal article (peer-reviewed)abstract
- Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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9. |
- Feroci, M., et al.
(author)
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LOFT - The large observatory for x-ray timing
- 2012
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9780819491442 ; , s. 84432D-
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Conference paper (peer-reviewed)abstract
- The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of <5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO's to yearlong transient outbursts. In this paper we report the current status of the project.
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10. |
- Feroci, M., et al.
(author)
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The large observatory for x-ray timing
- 2014
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819496126
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Conference paper (peer-reviewed)abstract
- The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
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11. |
- Walker, Anthony P, et al.
(author)
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Horizon 2020 EuPRAXIA design study
- 2017
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 874:1
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Journal article (peer-reviewed)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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12. |
- Gerin, M., et al.
(author)
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Interstellar OH+, H2O+ and H3O+ along the sight-line to G10.6-0.4
- 2010
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:4, s. 110-
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Journal article (peer-reviewed)abstract
- We report the detection of absorption lines by the reactive ions OH+, H2O+ and H3O+ along the line of sight to the submillimeter continuum source G10.6$-$0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+ at 971 GHz, H2O+ at 1115 and 607 GHz, and H3O+ at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6$-$0.4 as well as in the molecular gas directly associated with that source. The OH+ spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+ lines remains lower than 1 in the same velocity range, and the H3O+ line shows only weak absorption. For LSR velocities between 7 and 50 kms$^{-1}$ we estimate total column densities of $N$(OH+) $> 2.5 \times 10^{14}$ cm$^{-2}$, $N$(H2O+) $\sim 6 \times 10^{13}$ cm$^{-2}$ and $N$(H3O+) $\sim 4.0 \times 10^{13}$ cm$^{-2}$. These detections confirm the role of O$^+$ and OH$^+$ in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH+ by the H2O+ column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.
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13. |
- Neufeld, D. A., et al.
(author)
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Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
- 2010
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L10-
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Journal article (peer-reviewed)abstract
- We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH+ and the 1115 GHz 1(11)-0(00) transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s(-1) with respect to the local standard of rest. The inferred OH+/H2O+ abundance ratio ranges from similar to 3 to similar to 15, implying that the observed OH+ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few x10(-8) suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4 x 10(-16) s(-1), in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H-3(+) and other species.
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14. |
- Aubert, B., et al.
(author)
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Performance of the ATLAS electromagnetic calorimeter end-cap module 0
- 2003
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 500:03-jan, s. 178-201
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Journal article (peer-reviewed)abstract
- The construction and beam test results of the ATLAS electromagnetic end-cap calorimeter pre-production module 0 are presented. The stochastic term of the energy resolution is between 10% and 12.5% GeV1/2 over the full pseudorapidity range. Position and angular resolutions are found to be in agreement with simulation. A global constant term of 0.6% is obtained in the pseudorapidity range 2.5 < η < 3.2 (inner wheel).
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15. |
- Audet, T. L., et al.
(author)
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Electron injector for compact staged high energy accelerator
- 2016
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In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 829, s. 304-308
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Journal article (peer-reviewed)abstract
- An electron injector for multi-stage laser wakefield experiments is presented. It consists of a variable length gas cell of small longitudinal dimension (⩽10mm). The gas filling process in this cell was characterized both experimentally and with fluid simulation. Electron acceleration experiments were performed at two different laser facilities. Results show low divergence and low pointing fluctuation electron bunches suitable for transport to a second stage, and a peaked energy distribution suitable for injection into the second stage wakefield accelerator.
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16. |
- Desforges, F. G., et al.
(author)
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Analysis of Electron Injection in Laser Wakefield Acceleration Using Betatron Emission in Capillary Tubes
- 2015
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In: Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III. - : SPIE. - 1996-756X .- 0277-786X. ; 9514, s. 95140-95140
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Conference paper (peer-reviewed)abstract
- The dynamics of ionization-induced electron injection in the high density (similar to 1.2 x 10(19)cm(-3)) regime of Laser Wakefield Acceleration (LWFA) was investigated by analyzing betatron X-ray emission inside dielectric capillary tubes. A comparative study of the electron and betatron X-ray properties was performed for both self-injection and ionization-induced injection. Direct experimental evidence of early onset of ionization-induced injection into the plasma wave was obtained by mapping the X-ray emission zone inside the plasma. Particle-In-Cell (PIC) simulations showed that the early onset of ionization-induced injection, due to its lower trapping threshold, suppresses self-injection of electrons. An increase of X-ray fluence by at least a factor of two was observed in the case of ionization-induced injection due to an increased trapped charge compared to self-injection mechanism.
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17. |
- Desforges, F. G., et al.
(author)
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Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration
- 2014
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:12
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Journal article (peer-reviewed)abstract
- The dynamics of ionization-induced electron injection in high density (similar to 1.2 x 10(19) cm(-3)) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism. (C) 2014 AIP Publishing LLC.
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18. |
- Falgarone, E., et al.
(author)
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CH+(1-0) and 13CH+(1-0) absorption lines in the direction of massive star-forming regions
- 2010
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1
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Journal article (peer-reviewed)abstract
- We report the detection of the ground-state rotational transition of the methylidyne cation CH+ and its isotopologue (CH+)-C-13 toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH+ absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH+ column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [(CH+)-C-12]/[(CH+)-C-13]> 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH+)/N(HCO+), is found to vary by at least a factor 10, between 4 and > 40, in the Galactic foreground material. Line-of-sight 12CH+ average abundances relative to total hydrogen are estimated. Their average value, N(CH+)/NH > 2.6 x 10(-8), is higher than that observed in the solar neighborhood and confirms the high abundances of CH+ in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH+)/ N(HCO+) ratios, from 1 to similar to 50, is comparable to that observed.
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19. |
- Gallardo González, I., et al.
(author)
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Effects of the dopant concentration in laser wakefield and direct laser acceleration of electrons
- 2018
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 20:5
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Journal article (peer-reviewed)abstract
- In this work, we experimentally study the effects of the nitrogen concentration in laser wakefield acceleration of electrons in a gas mixture of hydrogen and nitrogen. A 15 TW peak power laser pulse is focused to ionize the gas, excite a plasma wave and accelerate electrons up to 230 MeV. We find that at dopant concentrations above 2% the total divergence of the electrons is increased and the high energy electrons are emitted preferentially with an angle of ±6 mrad, leading to a forked spatio-spectral distribution associated to direct laser acceleration (DLA). However, electrons can gain more energy and have a divergence lower than 4 mrad for concentrations below 0.5% and the same laser and plasma conditions. Particle-in-cell simulations show that for dopant concentrations above 2%, the amount of trapped charge is large enough to significantly perturb the plasma wave, reducing the amplitude of the longitudinal wakefield and suppressing other trapping mechanisms. At high concentrations the number of trapped electrons overlapping with the laser fields is increased, which rises the amount of charge affected by DLA. We conclude that the dopant concentration affects the quantity of electrons that experience significant DLA and the beam loading of the plasma wave driven by the laser pulse. These two mechanisms influence the electrons final energy, and thus the dopant concentration should be considered as a factor for the optimization of the electron beam parameters.
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20. |
- Hansson, M., et al.
(author)
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Localization of ionization-induced trapping in a laser wakefield accelerator using a density down-ramp
- 2016
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 58:5
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Journal article (peer-reviewed)abstract
- We report on a study on controlled trapping of electrons, by field ionization of nitrogen ions, in laser wakefield accelerators in variable length gas cells. In addition to ionization-induced trapping in the density plateau inside the cells, which results in wide, but stable, electron energy spectra, a regime of ionization-induced trapping localized in the density down-ramp at the exit of the gas cells, is found. The resulting electron energy spectra are peaked, with 10% shot-to-shot fluctuations in peak energy. Ionization-induced trapping of electrons in the density down-ramp is a way to trap and accelerate a large number of electrons, thus improving the efficiency of the laser-driven wakefield acceleration.
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21. |
- Ju, J., et al.
(author)
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Analysis of x-ray emission and electron dynamics in a capillary-guided laser wakefield accelerator
- 2014
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:5
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Journal article (peer-reviewed)abstract
- The dynamics of electron acceleration driven by laser wakefield inside a 30.5 mm long dielectric capillary tube is analyzed using radiation emitted in the x-ray range. 3D particle-in-cell simulations, performed with parameters close to the experimental ones, show that in long plasmas, the accelerated electrons catch up and finally overrun the driving laser owing to a higher velocity of the electrons in the plasma. The electrons are then transversely scattered by the laser pulse, and penetrate the capillary wall where they generate bremsstrahlung radiation, modeled using geant4 simulations. The signature of bremsstrahlung radiation is detected using an x-ray camera, together with the betatron radiation emitted during electron acceleration in the plasma bubble. The reflection of betatron radiation from the inner capillary surface also accounts for a fraction of the observed signal on the x-ray camera. The simulation results are in agreement with the experimental ones and provide a detailed description of the electron and radiation properties, useful for the design of laser wakefield accelerators or radiation sources using long plasma media.
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22. |
- Persson, Carina, 1964, et al.
(author)
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Nitrogen hydrides in interstellar gas Herschel/HIFI observations towards G10.6-0.4 (W31C)
- 2010
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L45 -
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Journal article (peer-reviewed)abstract
- The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N = 1
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23. |
- Abidi, S, et al.
(author)
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Standardised shorter regimens versus individualised longer regimens for rifampin- or multidrug-resistant tuberculosis
- 2020
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In: The European respiratory journal. - : European Respiratory Society (ERS). - 1399-3003 .- 0903-1936. ; 55:3
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Journal article (peer-reviewed)abstract
- We sought to compare the effectiveness of two World Health Organization (WHO)-recommended regimens for the treatment of rifampin- or multidrug-resistant (RR/MDR) tuberculosis (TB): a standardised regimen of 9–12 months (the “shorter regimen”) and individualised regimens of ≥20 months (“longer regimens”).We collected individual patient data from observational studies identified through systematic reviews and a public call for data. We included patients meeting WHO eligibility criteria for the shorter regimen: not previously treated with second-line drugs, and with fluoroquinolone- and second-line injectable agent-susceptible RR/MDR-TB. We used propensity score matched, mixed effects meta-regression to calculate adjusted odds ratios and adjusted risk differences (aRDs) for failure or relapse, death within 12 months of treatment initiation and loss to follow-up.We included 2625 out of 3378 (77.7%) individuals from nine studies of shorter regimens and 2717 out of 13 104 (20.7%) individuals from 53 studies of longer regimens. Treatment success was higher with the shorter regimen than with longer regimens (pooled proportions 80.0% versus 75.3%), due to less loss to follow-up with the former (aRD −0.15, 95% CI −0.17– −0.12). The risk difference for failure or relapse was slightly higher with the shorter regimen overall (aRD 0.02, 95% CI 0–0.05) and greater in magnitude with baseline resistance to pyrazinamide (aRD 0.12, 95% CI 0.07–0.16), prothionamide/ethionamide (aRD 0.07, 95% CI −0.01–0.16) or ethambutol (aRD 0.09, 95% CI 0.04–0.13).In patients meeting WHO criteria for its use, the standardised shorter regimen was associated with substantially less loss to follow-up during treatment compared with individualised longer regimens and with more failure or relapse in the presence of resistance to component medications. Our findings support the need to improve access to reliable drug susceptibility testing.
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24. |
- Andreev, N. E., et al.
(author)
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Analysis of laser wakefield dynamics in capillary tubes
- 2010
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
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Journal article (peer-reviewed)abstract
- A general approach to the modifications of the spectrum of a laser pulse interacting with matter is elaborated and used for spectral diagnostics of laser wakefield generation in guiding structures. Analytical predictions of the laser frequency red shift due to the wakefield excited in a capillary waveguide are confirmed by self-consistent modeling results. The role of ionization blue shift, and nonlinear laser pulse and wakefield dynamics on the spectrum modification, is analyzed for recent experiments on plasma wave excitation by an intense laser pulse guided in hydrogen-filled glass capillary tubes up to 8 cm long. The dependence of the spectral frequency shift, measured as a function of filling pressure, capillary tube length and incident laser energy, is in excellent agreement with the simulation results, and the associated longitudinal accelerating field is in the range 1-10 GV m(-1).
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25. |
- Audet, T. L., et al.
(author)
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Investigation of ionization-induced electron injection in a wakefield driven by laser inside a gas cell
- 2016
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 23:2
-
Journal article (peer-reviewed)abstract
- Ionization-induced electron injection was investigated experimentally by focusing a driving laser pulse with a maximum normalized potential of 1.2 at different positions along the plasma density profile inside a gas cell, filled with a gas mixture composed of 99%H2+1%N2. Changing the laser focus position relative to the gas cell entrance controls the accelerated electron bunch properties, such as the spectrum width, maximum energy, and accelerated charge. Simulations performed using the 3D particle-in-cell code WARP with a realistic density profile give results that are in good agreement with the experimental ones. The interest of this regime for optimizing the bunch charge in a selected energy window is discussed.
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26. |
- Desforges, F. G., et al.
(author)
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Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
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In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 54-59
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Journal article (peer-reviewed)abstract
- The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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27. |
- Dickson, L. T., et al.
(author)
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Mechanisms to control laser-plasma coupling in laser wakefield electron acceleration
- 2022
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In: Physical Review Accelerators and Beams. - 2469-9888. ; 25:10
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Journal article (peer-reviewed)abstract
- Experimental results, supported by precise modeling, demonstrate optimization of a plasma-based injector with intermediate laser pulse energy (<1 J), corresponding to a normalized vector potential a0=2.15, using ionization injection in a tailored plasma density profile. An increase in electron bunch quality and energy is achieved experimentally with the extension of the density downramp at the plasma exit. Optimization of the focal position of the laser pulse in the tailored plasma density profile is shown to efficiently reduce electron bunch angular deviation, leading to a better alignment of the electron bunch with the laser axis. Single peak electron spectra are produced in a previously unexplored regime by combining an early focal position and adaptive optic control of the laser wavefront by optimizing the symmetry of the prefocal laser energy distribution. Experimental results have been validated through particle-in-cell simulations using realistic laser energy, phase distribution, and temporal envelope, allowing for accurate predictions of difficult to model parameters, such as total charge and spatial properties of the electron bunches, opening the way for more accurate modeling for the design of plasma-based accelerators.
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28. |
- du Cros, P, et al.
(author)
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Standards for clinical trials for treating TB
- 2023
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In: The international journal of tuberculosis and lung disease : the official journal of the International Union against Tuberculosis and Lung Disease. - 1815-7920. ; 27:12, s. 885-898
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Journal article (peer-reviewed)
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29. |
- Filippi, F., et al.
(author)
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Plasma density profile reconstruction of a gas cell for Ionization Induced Laser Wakefield Acceleration
- 2023
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In: Journal of Instrumentation. - 1748-0221. ; 18:5
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Journal article (peer-reviewed)abstract
- Laser-driven plasma wakefields can provide hundreds of MeV electron beam in mm-range distances potentially shrinking the dimension of the actual particle accelerators. The plasma density plays a fundamental role in the control and stability of the acceleration process, which is a key development for the future electron injector proposed by EuPRAXIA. A gas cell was designed by LPGP and LIDYL teams, with variable length and backing pressure, to confine the gas and tailor the gas density profile before the arrival of the laser. This cell was used during an experimental campaign with the multi TW-class laser at the Lund Laser Centre. Ionization assisted injection in a tailored density profile is used to tune the electron beam properties. During the experiment, we filled the gas cell with hydrogen mixed with different concentration of nitrogen. We also varied the backing pressure of the gas and the geometrical length of the gas cell. We used a transverse probe to acquire shadowgraphic images of the plasma and to measure the plasma electron density. Methods and results of the analysis with comparisons between shadowgraphic and interferometric images will be discussed.
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30. |
- Genoud, Guillaume, et al.
(author)
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Laser-plasma electron acceleration in dielectric capillary tubes
- 2011
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 105:2, s. 309-316
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Journal article (peer-reviewed)abstract
- Electron beams and betatron X-ray radiation generated by laser wakefield acceleration in long plasma targets are studied. The targets consist of hydrogen filled dielectric capillary tubes of diameter 150 to 200 microns and length 6 to 20 mm. Electron beams are observed for peak laser intensities as low as 5x10(17) W/cm(2). It is found that the capillary collects energy outside the main peak of the focal spot and contributes to keep the beam self-focused over a distance longer than in a gas jet of similar density. This enables the pulse to evolve enough to reach the threshold for wavebreaking, and thus trap and accelerate electrons. No electrons were observed for capillaries of large diameter (250 mu m), confirming that the capillary influences the interaction and does not have the same behaviour as a gas cell. Finally, X-rays are used as a diagnostic of the interaction and, in particular, to estimate the position of the electrons trapping point inside the capillary.
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31. |
- Hansson, Martin, et al.
(author)
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Enhanced stability of laser wakefield acceleration using dielectric capillary tubes
- 2014
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:3
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Journal article (peer-reviewed)abstract
- The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.
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32. |
- Ju, J., et al.
(author)
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Enhancement of x-rays generated by a guided laser wakefield accelerator inside capillary tubes
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:19
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Journal article (peer-reviewed)abstract
- Abstract in UndeterminedElectrons accelerated in the nonlinear regime in a laser wakefield accelerator experience transverse oscillations inside the plasma cavity, giving rise to ultra-short pulsed x-rays, also called the betatron radiation. We show that the fluence of x-ray can be enhanced by more than one order of magnitude when the laser is guided by a 10 mm long capillary tube instead of interacting with a 2 mm gas jet. X-rays with a synchrotron-like spectrum and associated critical energy ∼ 5 keV, with a peak brightness of ∼ 1×1021 ph/s/mm2/mrad2/0.1%BW, were achieved by employing 16 TW laser pulses.
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33. |
- Ju, J., et al.
(author)
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Study of electron acceleration and x-ray radiation as a function of plasma density in capillary-guided laser wakefield accelerators
- 2013
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:8
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Journal article (peer-reviewed)abstract
- Laser wakefield electron acceleration in the blow-out regime and the associated betatron X-ray radiation were investigated experimentally as a function of the plasma density in a configuration where the laser is guided. Dielectric capillary tubes were employed to assist the laser keeping self-focused over a long distance by collecting the laser energy around its central focal spot. With a 40 fs, 16 TW pulsed laser, electron bunches with tens of pC charge were measured to be accelerated to an energy up to 300 MeV, accompanied by X-ray emission with a peak brightness of the order of 10 21 ph/s/mm(2)/mrad(2)/0.1%BW. Electron trapping and acceleration were studied using the emitted X-ray beam distribution to map the acceleration process; the number of betatron oscillations performed by the electrons was inferred from the correlation between measured X-ray fluence and beam charge. A study of the stability of electron and X-ray generation suggests that the fluctuation of X-ray emission can be reduced by stabilizing the beam charge. The experimental results are in good agreement with 3D particle-in-cell (PIC) simulation. (C) 2013 AIP Publishing LLC.
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34. |
- Mangles, S. P. D., et al.
(author)
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Controlling the spectrum of x-rays generated in a laser-plasma accelerator by tailoring the laser wavefront
- 2009
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:18
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Journal article (peer-reviewed)abstract
- By tailoring the wavefront of the laser pulse used in a laser-wakefield accelerator, we show that the properties of the x-rays produced due to the electron beam's betatron oscillations in the plasma can be controlled. By creating a wavefront with coma, we find that the critical energy of the synchrotronlike x-ray spectrum can be significantly increased. The coma does not substantially change the energy of the electron beam, but does increase its divergence and produces an energy-dependent exit angle, indicating that changes in the x-ray spectrum are due to an increase in the electron beam's oscillation amplitude within the wakefield.
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35. |
- Marangolo, M, et al.
(author)
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Magnetism of the Fe/ZnSe(001) interface
- 2002
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 88:21, s. 217202-
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Journal article (peer-reviewed)abstract
- The magnetism of epitaxial ultrathin films of Fe on ZnSe(001) has been investigated by x-ray magnetic circular dichroism down to the submonolayer regime. In contrast to other metallic ferromagnet/semiconductor interfaces, no reduction of the Fe magnetic moment was found at the Fe/ZnSe(001) interface. Furthermore, a significant enhancement of the Fe magnetic moment compared to the bulk value was observed for coverages up to one monolayer in agreement with theoretical predictions. We also demonstrate that the magnetic properties of the Fe/ZnSe(001) interface remain stable against thermal annealing up to 300 degrees C, a prerequisite for the future development of efficient spintronics devices.
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36. |
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37. |
- Wojda, F., et al.
(author)
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Laser-driven plasma waves in capillary tubes
- 2009
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In: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 80:6
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Journal article (peer-reviewed)abstract
- The excitation of plasma waves over a length of up to 8 cm is demonstrated using laser guiding of intense laser pulses through hydrogen-filled glass capillary tubes. The plasma waves are diagnosed by spectral analysis of the transmitted laser radiation. The dependence of the spectral redshift-measured as a function of filling pressure, capillary tube length, and incident laser energy-is in excellent agreement with simulation results. The longitudinal accelerating field inferred from the simulations is in the range of 1-10 GV/m.
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