| 1. |
- 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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| 2. |
- 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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| 3. |
- Mangles, SPD, et al.
(författare)
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Effect of contrast ratio on electron beam stability in laser wakefield acceleration experiments
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335. ; 48:12B, s. 83-90
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Tidskriftsartikel (refereegranskat)abstract
- Laser wakefield accelerators offer the possibility of compact electron acceleration. However one of the key outstanding issues with the results reported to date is the electron beam stability. Experiments on two laser systems reveal that the contrast ratio between the ASE pedestal and main pulse is an important factor in determining the quality of the electron beam. With a high contrast ratio (10^8) the electron beam profile is a well collimated single beam having a low pointing instability (<10 mrad rms). With a lower contrast (10^6) the beam profile contains multiple beamlets which exhibit a large pointing instability (~50 mrad rms). Ahigh contrast ratio not only improves the beam pointing stability (~6 mrad) but also stabilizes the electron beam energy reproducibility (5%).
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| 4. |
- Mangles, SPD, et al.
(författare)
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Laser-wakefield acceleration of monoenergetic electron beams in the first plasma-wave period
- 2006
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Ingår i: Physical Review Letters. - 1079-7114. ; 96:21
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Tidskriftsartikel (refereegranskat)abstract
- Beam profile measurements of laser-wakefield accelerated electron bunches reveal that in the monoenergetic regime the electrons are injected and accelerated at the back of the first period of the plasma wave. With pulse durations c tau >=lambda(p), we observe an elliptical beam profile with the axis of the ellipse parallel to the axis of the laser polarization. This increase in divergence in the laser polarization direction indicates that the electrons are accelerated within the laser pulse. Reducing the plasma density (decreasing c tau/lambda(p)) leads to a beam profile with less ellipticity, implying that the self-injection occurs at the rear of the first period of the plasma wave. This also demonstrates that the electron bunches are less than a plasma wavelength long, i.e., have a duration < 25 fs. This interpretation is supported by 3D particle-in-cell simulations.
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| 5. |
- Mangles, S. P. D., et al.
(författare)
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On the stability of laser wakefield electron accelerators in the monoenergetic regime
- 2007
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 14:5
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Tidskriftsartikel (refereegranskat)abstract
- The effects of plasma density and laser energy on the stability of laser produced monoenergetic electron beams are investigated. Fluctuations in the principal beam parameters, namely, electron energy, energy-spread, charge, and pointing, are demonstrated to be minimized at low densities. This improvement in stability is attributed to the reduced time for pulse evolution required before self-injection occurs; i.e., that the pulse is closest to the matched conditions for these densities. It is also observed that electrons are only consistently produced above a density-dependent energy threshold. These observations are consistent with there being a threshold intensity (a(0)greater than or similar to 3) required for the occurrence of self-injection after accounting for pulse compression. (C) 2007 American Institute of Physics.
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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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