13 results found
Streeter M, Najmudin Z, Shalloo R, et al., 2020, Automation and control of laser wakefield accelerators using Bayesian optimisation, Nature Communications, Vol: 11, Pages: 1-8, ISSN: 2041-1723
Laser wakefield accelerators promise to revolutionize many areas of accelerator science. However, one of the greatest challenges to their widespread adoption is the difficulty in control and optimization of the accelerator outputs due to coupling between input parameters and the dynamic evolution of the accelerating structure. Here, we use machine learning techniques to automate a 100 MeV-scale accelerator, which optimized its outputs by simultaneously varying up to six parameters including the spectral and spatial phase of the laser and the plasma density and length. Most notably, the model built by the algorithm enabled optimization of the laser evolution that might otherwise have been missed in single-variable scans. Subtle tuning of the laser pulse shape caused an 80% increase in electron beam charge, despite the pulse length changing by just 1%.
Gruse J-N, Streeter MJV, Thornton C, et al., 2020, Application of compact laser-driven accelerator X-ray sources for industrial imaging, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, Vol: 983, Pages: 1-7, ISSN: 0168-9002
X-rays generated by betatron oscillations of electrons in a laser-driven plasma accelerator were charac-terised and applied to imaging industrial samples. With a125TWlaser, a low divergence beam with5.2 ± 1.7 × 107photonsmrad−2per pulse was produced with a synchrotron spectrum with a critical energy of14.6 ± 1.3keV. Radiographs were obtained of a metrology test sample, battery electrodes, and a damage sitein a composite material. These results demonstrate the suitability of the source for non-destructive evaluationapplications. The potential for industrial implementation of plasma accelerators is discussed.
Streeter M, Shalloo R, Dann S, 2020, Code and data associated with Automation and control of laser wakefield accelerators using Bayesian optimisation
This repository contains the basic code for the article Automation and control of laser wakefield accelerators using Bayesian optimisation. It also contains the data and code to reproduce figure 3 and a video from an FBPIC simulation used in figure 5.
Kettle B, Gerstmayr E, Streeter MJV, et al., 2019, Single-shot multi-keV X-ray absorption spectroscopy using an ultrashort laser-wakefield accelerator source, Physical Review Letters, Vol: 123, Pages: 254801-1-254801-6, ISSN: 0031-9007
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.
Hussein AE, Senabulya N, Ma Y, et al., 2019, Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures, Scientific Reports, Vol: 9, Pages: 1-13, ISSN: 2045-2322
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.
Nghiem PAP, Alesini D, Aschikhin A, et al., 2019, EuPRAXIA, A STEP TOWARD A PLASMA-WAKEFIELD BASED ACCELERATOR WITH HIGH BEAM QUALITY, 10th International Particle Accelerator Conference (IPAC), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Streeter M, Kneip S, Bloom M, et al., 2018, Observation of laser power amplification in a self-injecting laser wakefield accelerator, Physical Review Letters, Vol: 120, Pages: 254801-1-254801-6, ISSN: 0031-9007
We report on the depletion and power ampli cation of the driving laser pulse in a strongly-drivenlaser wake eld accelerator. Simultaneous measurement of the transmitted pulse energy and temporalshape indicate an increase in peak power from 18711 TW to a maximum of 31812 TW after13 mm of propagation in plasma density of 0:91018cm3. The power ampli cation is correlatedwith the injection and acceleration of electrons in the non-linear wake eld. This process is modeledby including localized redshift and subsequent group delay dispersion at the laser pulse front.
Streeter M, Dann S, Scott JDE, et al., 2018, Temporal feedback control of high-intensity laser pulses to optimize ultrafast heating of atomic clusters, Applied Physics Letters, Vol: 112, Pages: 244101-1-244101-5, ISSN: 1077-3118
We describe how active feedback routines can be applied at limited repetition rate (5 Hz) to optimize high-power (P>10 TW) laser interactions with clustered gases. Optimization of x-ray production from anargon cluster jet, using a genetic algorithm, approximately doubled the measured energy through temporalmodification of the 150 mJ driving laser pulse. This approach achieved an increased radiation yield throughexploration of a multi-dimensional parameter space, without requiring detailedaprioriknowledge of thecomplex cluster dynamics. The optimized laser pulses exhibited a slow rising edge to the intensity profile,which enhanced the laser energy coupling into the cluster medium, compared to the optimally compressedFWHM pulse (40 fs). Our work suggests that this technique can be more widely utilized for control of intensepulsed secondary radiation from petawatt-class laser systems.
Dover N, Palmer CAJ, Streeter MJV, et al., 2016, Buffered high charge spectrally-peaked proton beams in the relativistic-transparency regime, New Journal of Physics, Vol: 18, ISSN: 1367-2630
Spectrally-peaked proton beams of high charge (Ep ≈ 8 MeV, ∆E ≈4 MeV, N ≈ 50 nC ) have been observed from the interaction of an intense laser(> 1019 Wcm−2) with ultrathin CH foils, as measured by spectrally-resolved full beamprofiles. These beams are reproducibly generated for foil thicknesses 5-100 nm, andexhibit narrowing divergence with decreasing target thickness down to ≈ 8◦for 5 nm.Simulations demonstrate that the narrow energy spread feature is a result of bufferedacceleration of protons. The radiation pressure at the front of the target results inasymmetric sheath fields which permeate throughout the target, causing preferentialforward acceleration. Due to their higher charge-to-mass ratio, the protons outrun acarbon plasma driven in the relativistic transparency regime.
Gwynne D, Kar S, Doria D, et al., 2014, Modified Thomson spectrometer design for high energy, multi-species ion sources, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 85, ISSN: 0034-6748
Prasad R, Doria D, Ter-Avetisyan S, et al., 2010, Calibration of Thomson parabola-MCP assembly for multi-MeV ion spectroscopy, 1st International Conference on Frontiers in Diagnostic Technologies, Publisher: ELSEVIER, Pages: 712-715, ISSN: 0168-9002
Kneip S, Nagel SR, Martins SF, et al., 2009, Near-GeV Acceleration of Electrons by a Nonlinear Plasma Wave Driven by a Self-Guided Laser Pulse, PHYSICAL REVIEW LETTERS, Vol: 103, ISSN: 0031-9007
Rowlands-Rees TP, Kamperidis C, Kneip S, et al., 2008, Laser-driven acceleration of electrons in a partially ionized plasma channel, PHYSICAL REVIEW LETTERS, Vol: 100, ISSN: 0031-9007
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