| 1. |
- Magnusson, Joel, 1991, et al.
(author)
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Effect of electron-beam energy chirp on signatures of radiation reaction in laser-based experiments
- 2023
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In: Physical Review Accelerators and Beams. - 2469-9888. ; 26
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Journal article (peer-reviewed)abstract
- Current experiments investigating radiation reaction employ high energy electron beams together with tightly focused laser pulses in order to reach the quantum regime, as expressed through the quantum nonlinearity parameter χ. Such experiments are often complicated by the large number of latent variables, including the precise structure of the electron bunch. Here we examine a correlation between the electron spatial and energy distributions, called an energy chirp, investigate its significance to the laser-electron beam interaction and show that the resulting effect cannot be trivially ignored when analyzing current experiments. In particular, we show that the energy chirp has a large effect on the second central moment of the electron energy, but a lesser impact on the first electron energy moment or the photon critical energy. These results show the importance of improved characterization and control over electron bunch parameters on a shot-to-shot basis in such experiments.
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| 2. |
- Maitrallain, A., et al.
(author)
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Parametric study of high-energy ring-shaped electron beams from a laser wakefield accelerator
- 2022
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 24:1
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Journal article (peer-reviewed)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. |
- Spesyvtsev, R., et al.
(author)
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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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In: Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III. - : SPIE. - 9781510627383 ; 11036
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Conference paper (peer-reviewed)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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| 4. |
- Hussein, A. E., et al.
(author)
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Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures
- 2019
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1
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Journal article (peer-reviewed)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. |
- Kettle, B., et al.
(author)
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Single-Shot Multi-keV X-Ray Absorption Spectroscopy Using an Ultrashort Laser-Wakefield Accelerator Source
- 2019
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In: Physical Review Letters. - 0031-9007. ; 123:25
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Journal article (peer-reviewed)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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| 6. |
- Streeter, M. J.V., et al.
(author)
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Characterization of laser wakefield acceleration efficiency with octave spanning near-IR spectrum measurements
- 2022
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In: Physical Review Accelerators and Beams. - 2469-9888. ; 25:10
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Journal article (peer-reviewed)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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| 7. |
- Arran, C., et al.
(author)
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Optimal parameters for radiation reaction experiments
- 2019
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:7
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Journal article (peer-reviewed)abstract
- As new laser facilities are developed with intensities on the scale of 10(22)-10(24) W cm(-2), it becomes ever more important to understand the effect of strong field quantum electrodynamic processes, such as quantum radiation reaction, which will play a dominant role in laser-plasma interactions at these intensities. Recent all-optical experiments, where GeV electrons from a laser wakefield accelerator encountered a counter-propagating laser pulse with a(0) > 10, have produced evidence of radiation reaction, but have not conclusively identified quantum effects nor their most suitable theoretical description. Here we show the number of collisions and the conditions required to accomplish this, based on a simulation campaign of radiation reaction experiments under realistic conditions. We conclude that while the critical energy of the photon spectrum distinguishes classical and quantum-corrected models, a better means of distinguishing the stochastic and deterministic quantum models is the change in the electron energy spread. This is robust against shot-to-shot fluctuations and the necessary laser intensity and electron beam energies are already available. For example, we show that so long as the electron energy spread is below 25%, collisions at a(0) = 10 with electron energies of 500 MeV could differentiate between different quantum models in under 30 shots, even with shot-to-shot variations at the 50% level.
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| 8. |
- Arran, C., et al.
(author)
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Potential to measure quantum effects in recent all-optical radiation reaction experiments
- 2019
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11039
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Conference paper (peer-reviewed)abstract
- The construction of 10 PW class laser facilities with unprecedented intensities has emphasized the need for a thorough understanding of the radiation reaction process. We describe simulations for a recent all-optical colliding pulse experiment, where a GeV scale electron bunch produced by a laser wakefield accelerator interacted with a counter-propagating laser pulse. In the rest frame of the electron bunch, the electric field of the laser pulse is increased by several orders of magnitude, approaching the Schwinger field and leading to substantial variation from the classical Landau-Lifshitz model. Our simulations show how the final electron and photon spectra may allow us to differentiate between stochastic and semi-classical models of radiation reaction, even when there is significant shot-to-shot variation in the experimental parameters. In particular, constraints are placed on the maximum energy spread and shot-to-shot variation permissible if a stochastic model is to be proven with confidence.
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| 9. |
- Behm, K. T., et al.
(author)
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A spectrometer for ultrashort gamma-ray pulses with photon energies greater than 10 MeV
- 2018
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 89:11
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Journal article (peer-reviewed)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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| 10. |
- Blackburn, Thomas, 1989, et al.
(author)
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Model-independent inference of laser intensity
- 2020
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In: Physical Review Accelerators and Beams. - 2469-9888. ; 23:6
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Journal article (peer-reviewed)abstract
- An ultrarelativistic electron beam passing through an intense laser pulse emits radiation around its direction of propagation into a characteristic angular profile. Here, we show that measurement of the variances of this profile in the planes parallel and perpendicular to the laser polarization, and the mean initial and final energies of the electron beam, allows the intensity of the laser pulse to be inferred in a way that is independent of the model of the electron dynamics. The method presented applies whether radiation reaction is important or not, and whether it is classical or quantum in nature, with an accuracy of a few percent across 3 orders of magnitude in intensity. It is tolerant of electron beams with a broad energy spread and finite divergence. In laser-electron-beam collision experiments, where spatiotemporal fluctuations cause the alignment of the beams to vary from shot to shot, this permits inference of the laser intensity at the collision point, thereby facilitating comparisons between theoretical calculations and experimental data.
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| 11. |
- Cole, J. M., et al.
(author)
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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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In: Physical Review X. - 2160-3308. ; 8:1
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Journal article (peer-reviewed)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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| 12. |
- Fleck, K., et al.
(author)
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Dependence of the number-weighted angular distribution of Compton-scattered photon beams on the laser intensity
- 2024
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In: PHYSICAL REVIEW A. - 2469-9926 .- 2469-9934. ; 110:2
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Journal article (peer-reviewed)abstract
- Inverse Compton scattering of ultra-relativistic electron beams in the field of a high-intensity laser produces photon beams with angular and spectral distributions that are strongly dependent on the laser intensity. Here we show that the laser intensity at the interaction point can be accurately inferred from the measurement of the angular number-density distribution of Compton-scattered photon beams. The theoretical expressions, supported by numerical simulations, are accurate to within 10%-15% in a wide range of laser intensities (dimensionless intensity 5 a0 50) and electron energies (250 MeV E 15 GeV), and accounts for experimental features such as the finite transverse size of the electron beam, low-energy cutoffs in the photon detector, and the possibility of a transverse misalignment between the electron beam and the laser focus.
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| 13. |
- Kettle, Brendan, et al.
(author)
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Extended X-ray absorption spectroscopy using an ultrashort pulse laboratory-scale laser-plasma accelerator
- 2024
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In: Communications Physics. - 2399-3650. ; 7:1
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Journal article (peer-reviewed)abstract
- Laser-driven compact particle accelerators can provide ultrashort pulses of broadband X-rays, well suited for undertaking X-ray absorption spectroscopy measurements on a femtosecond timescale. Here the Extended X-ray Absorption Fine Structure (EXAFS) features of the K-edge of a copper sample have been observed over a 250 eV window in a single shot using a laser wakefield accelerator, providing information on both the electronic and ionic structure simultaneously. This capability will allow the investigation of ultrafast processes, and in particular, probing high-energy-density matter and physics far-from-equilibrium where the sample refresh rate is slow and shot number is limited. For example, states that replicate the tremendous pressures and temperatures of planetary bodies or the conditions inside nuclear fusion reactions. Using high-power lasers to pump these samples also has the advantage of being inherently synchronised to the laser-driven X-ray probe. A perspective on the additional strengths of a laboratory-based ultrafast X-ray absorption source is presented.
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