Publications
182 results found
Baird CD, Murphy CD, Blackburn TG, et al., 2019, Realising single-shot measurements of quantum radiation reaction in high-intensity lasers, New Journal of Physics, Vol: 21, ISSN: 1367-2630
Modern laser technology is now sufficiently advanced that collisions between high-intensity laser pulses and laser-wakefield-accelerated (LWFA) electron beams can reach the strong-field regime, so that it is possible to measure the transition between the classical and quantum regimes of light–matter interactions. However, the energy spectrum of LWFA electron beams can fluctuate significantly from shot to shot, making it difficult to clearly discern quantum effects in radiation reaction (RR), for example. Here we show how this can be accomplished in only a single laser shot. A millimetre-scale pre-collision drift allows the electron beam to expand to a size larger than the laser focal spot and develop a correlation between transverse position and angular divergence. In contrast to previous studies, this means that a measurement of the beam's energy-divergence spectrum automatically distinguishes components of the beam that hit or miss the laser focal spot and therefore do and do not experience RR.
Gould O, Mangles S, Rajantie A, et al., 2019, Observing thermal Schwinger pair production, Physical Review A, Vol: 99, ISSN: 1050-2947
We study the possibility of observing Schwinger pair production enhanced by a thermal bath of photons. We consider the full range of temperatures and electric field intensities from pure Schwinger production to pure thermal production, and identify the most promising and interesting regimes. In particular, we identify temperatures of ∼ 20 keV/kB and field intensities of ∼ 10²³ W cm¯² where pair production would be observable. In this case, the thermal enhancement over the Schwinger rate is exponentially large and due to effects which are not visible at any finite order in the loop expansion. Pair production in this regime can thus be described as more nonperturbative than the usual Schwinger process, which appears at one loop. Unfortunately, such high temperatures appear to be out of reach of foreseeable technologies, though nonthermal photon distributions with comparable energy densities are possible. We suggest the possibility that similar nonperturbative enhancements may extend out of equilibrium and propose an experimental scheme to test this.
Dann SJD, Baird CD, Bourgeois N, et al., 2019, Laser wakefield acceleration with active feedback at 5 Hz, Physical Review Accelerators and Beams, Vol: 22, ISSN: 2469-9888
We describe the use of a genetic algorithm to apply active feedback to a laser wakefield accelerator at a higher power (10 TW) and a lower repetition rate (5 Hz) than previous work. The temporal shape of the drive laser pulse was adjusted automatically to optimize the properties of the electron beam. By changing the software configuration, different properties could be improved. This included the total accelerated charge per bunch, which was doubled, and the average electron energy, which was increased from 22 to 27 MeV. Using experimental measurements directly to provide feedback allows the system to work even when the underlying acceleration mechanisms are not fully understood, and, in fact, studying the optimized pulse shape might reveal new insights into the physical processes responsible. Our work suggests that this technique, which has already been applied with low-power lasers, can be extended to work with petawatt-class laser systems.
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.
Turcu ICE, Shen B, Neely D, et al., 2019, Quantum electrodynamics experiments with colliding petawatt laser pulses, High Power Laser Science and Engineering, Vol: 7, ISSN: 2095-4719
A new generation of high power laser facilities will provide laser pulses with extremely high powers of 10 petawatt (PW)and even 100 PW, capable of reaching intensities of 1023W/cm2in the laser focus. These ultra-high intensities arenevertheless lower than the Schwinger intensityIS=2.3×1029W/cm2at which the theory of quantum electrodynamics(QED) predicts that a large part of the energy of the laser photons will be transformed to hard Gamma-ray photonsand even to matter, via electron–positron pair production. To enable the investigation of this physics at the intensitiesachievable with the next generation of high power laser facilities, an approach involving the interaction of two collidingPW laser pulses is being adopted. Theoretical simulations predict strong QED effects with colliding laser pulses of>10 PW focused to intensities>1022W/cm2.
Weikum MK, Akhter T, Alesini D, et al., 2019, Status of the Horizon 2020 EuPRAXIA conceptual design study, 10th International Particle Accelerator Conference (IPAC), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 8
Weikum MK, Akhter T, Alesini PD, et al., 2019, EuPRAXIA - A Compact, Cost-Efficient Particle and Radiation Source, 25th International Conference on the Application of Accelerators in Research and Industry (CAARI), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
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- Citations: 4
Spesyvtsev R, Brunetti E, Vieux G, et al., 2019, Generation of electron high energy beams with a ring-like structure by a dual stage laser wakefield accelerator, Conference on Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
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- Citations: 1
Arran C, Cole JM, Gerstmayr E, et al., 2019, Potential to measure quantum effects in recent all-optical radiation reaction experiments, Conference on Research Using Extreme Light - Entering New Frontiers with Petawatt-Class Lasers IV, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Warwick JR, Alejo A, Dzelzainis T, et al., 2018, General features of experiments on the dynamics of laser-driven electron-positron beams, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 909, Pages: 95-101, ISSN: 0168-9002
The experimental study of the dynamics of neutral electron–positron beams is an emerging area of research, enabled by the recent results on the generation of this exotic state of matter in the laboratory. Electron–positron beams and plasmas are believed to play a major role in the dynamics of extreme astrophysical objects such as supermassive black holes and pulsars. For instance, they are believed to be the main constituents of a large number of astrophysical jets, and they have been proposed to significantly contribute to the emission of gamma-ray bursts and their afterglow. However, despite extensive numerical modelling and indirect astrophysical observations, a detailed experimental characterisation of the dynamics of these objects is still at its infancy. Here, we will report on some of the general features of experiments studying the dynamics of electron–positron beams in a fully laser-driven setup.
Behm KT, Cole JM, Joglekar AS, et al., 2018, A spectrometer for ultrashort gamma-ray pulses with photon energies greater than 10 MeV, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 89, ISSN: 0034-6748
Krushelnick K, Dangor AE, Kaluza M, et al., 2018, Observation of anomalous side-scattering in laser waketield accelerators, LASER AND PARTICLE BEAMS, Vol: 36, Pages: 391-395, ISSN: 0263-0346
Wood JC, Chapman DJ, Poder K, et al., 2018, Ultrafast imaging of laser driven shock waves using Betatron x-rays from a laser Wakefield accelerator, Scientific Reports, Vol: 8, ISSN: 2045-2322
Betatron radiation from laser wakefield accelerators is an ultrashort pulsedsource of hard, synchrotron-like x-ray radiation. It emanates from a centimetrescale plasma accelerator producing GeV level electron beams. In recent yearsbetatron radiation has been developed as a unique source capable of producinghigh resolution x-ray images in compact geometries. However, until now, theshort pulse nature of this radiation has not been exploited. This reportdetails the first experiment to utilise betatron radiation to image a rapidlyevolving phenomenon by using it to radiograph a laser driven shock wave in asilicon target. The spatial resolution of the image is comparable to what hasbeen achieved in similar experiments at conventional synchrotron light sources.The intrinsic temporal resolution of betatron radiation is below 100 fs,indicating that significantly faster processes could be probed in futurewithout compromising spatial resolution. Quantitative measurements of the shockvelocity and material density were made from the radiographs recorded duringshock compression and were consistent with the established shock response ofsilicon, as determined with traditional velocimetry approaches. This suggeststhat future compact betatron imaging beamlines could be useful in the imagingand diagnosis of high-energy-density physics experiments.
Wood JC, Chapman D, Poder K, et al., 2018, Ultrafast Imaging of Laser Driven Shock Waves using Betatron X-rays from a Laser Wakefield Accelerator, Scientific Reports, ISSN: 2045-2322
Schumaker W, Liang T, Clarke R, et al., 2018, Making pions with laser light, NEW JOURNAL OF PHYSICS, Vol: 20, ISSN: 1367-2630
Poder K, Tamburini M, Sarri G, et al., 2018, Experimental signatures of the quantum nature of radiation reaction in the field of an ultraintense laser, Physical Review X, Vol: 8, ISSN: 2160-3308
The description of the dynamics of an electron in an external electromagnetic field of arbitrary intensity is one of the most fundamental outstanding problems in electrodynamics. Remarkably, to date, there is no unanimously accepted theoretical solution for ultrahigh intensities and little or no experimental data. The basic challenge is the inclusion of the self-interaction of the electron with the field emitted by the electron itself—the so-called radiation reaction force. We report here on the experimental evidence of strong radiation reaction, in an all-optical experiment, during the propagation of highly relativistic electrons (maximum energy exceeding 2 GeV) through the field of an ultraintense laser (peak intensity of 4×1020 W/cm2). In their own rest frame, the highest-energy electrons experience an electric field as high as one quarter of the critical field of quantum electrodynamics and are seen to lose up to 30% of their kinetic energy during the propagation through the laser field. The experimental data show signatures of quantum effects in the electron dynamics in the external laser field, potentially showing departures from the constant cross field approximation.
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.
Cole JM, Symes DR, Lopes NC, et al., 2018, High-resolution mu CT of a mouse embryo using a compact laser-driven X-ray betatron source, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 115, Pages: 6335-6340, ISSN: 0027-8424
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.
McGuffey C, Schumaker W, Matsuoka T, et al., 2018, On the properties of synchrotron-like X-ray emission from laser wakefield accelerated electron beams, PHYSICS OF PLASMAS, Vol: 25, ISSN: 1070-664X
Symes DR, Brenner CM, Rusby DR, et al., 2018, Optimisation of compact laser driven accelerator X-ray sources for industrial imaging applications
Compact laser-driven electron accelerators can produce coherent x-ray beams with high brightness, small source-size and femtosecond duration. We will discuss the suitability of these sources to address challenges in industrial imaging.
Cole JM, Behm KT, Blackburn TG, et al., 2018, Experimental evidence of radiation reaction in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam, Physical Review X, Vol: 8, ISSN: 2160-3308
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 (ϵ>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 ϵcrit>30 MeV.
Warwick J, Dzelzainis T, Dieckmann ME, et al., 2017, Experimental observation of a current-driven instability in a neutral electron-positron beam, Physical Review Letters, Vol: 119, ISSN: 0031-9007
We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥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 εB≈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.
Poder K, Cole JM, Wood JC, et al., 2017, Measurements of self-guiding of ultrashort laser pulses over long distances, Plasma Physics and Controlled Fusion, Vol: 60, ISSN: 0741-3335
We report on the evaluation of the performance of self-guiding over extended distances with $f/20$ and $f/40$ focussing geometries. Guiding over $39\,\mathrm{mm}$ or more than 100 Rayleigh ranges was observed with the $f/20$ optic at ${n}_{e}=1.5\times {10}^{18}\,{\mathrm{cm}}^{-3}$. Analysis of guiding performance found that the extent of the exiting laser spatial mode closely followed the matched spot size predicted by 3D nonlinear theory. Self-guiding with an $f/40$ optic was also characterised, with guided modes observed for a plasma length of $90\,\mathrm{mm}$ and a plasma density of ${n}_{e}=9.5\times {10}^{17}\,{\mathrm{cm}}^{-3}$. This corresponds to self-guided propagation over 53 Rayleigh ranges and is similar to distances obtained with discharge plasma channel guiding.
Ridgers CP, Blackburn TG, Del Sorbo D, et al., 2017, Signatures of quantum effects on radiation reaction in laser-electron-beam collisions, JOURNAL OF PLASMA PHYSICS, Vol: 83, ISSN: 0022-3778
Cowley J, Thornton C, Arran C, et al., 2017, Excitation and control of plasma wakefields by multiple laser pulses, Physical Review Letters, Vol: 119, ISSN: 1079-7114
We demonstrate experimentally the resonant excitation of plasma waves by trains of laser pulses. We also take an important first step to achieving an energy recovery plasma accelerator by showing that a plasma wave can be damped by an out-of-resonance trailing laser pulse. The measured laser wakefields are found to be in excellent agreement with analytical and numerical models of wakefield excitation in the linear regime. Our results indicate a promising direction for achieving highly controlled, GeV-scale laser-plasma accelerators operating at multikilohertz repetition rates.
Walker PA, Alesini PD, Alexandrova AS, et al., 2017, Horizon 2020 EuPRAXIA design study, 8th International Particle Accelerator Conference (IPAC), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Mangles SPD, Smid M, Gallardo Gonzalez I, et al., 2017, Highly efficient angularly resolving x-ray spectrometer optimized for absorption measurements with collimated sources, Review of Scientific Instruments, Vol: 88, ISSN: 1089-7623
Highly collimated betatron radiation from a laser wakefield accelerator is a promising tool for spectroscopic measurements. Therefore, there is a requirement to create spectrometers suited to the unique properties of such a source. We demonstrate a spectrometer which achieves an energy resolution of <5 eV at 9 keV (E∕ΔE>1800) and is angularly resolving the x-ray emission allowing the reference and spectrum to be recorded at the same time. The single photon analysis is used to significantly reduce the background noise. Theoretical performance of various configurations of the spectrometer is calculated by a ray-tracing algorithm. The properties and performance of the spectrometer including the angular and spectral resolution are demonstrated experimentally on absorption above the K-edge of a Cu foil backlit by a laser-produced betatron radiation x-ray beam.
Sarri G, Warwick J, Schumaker W, et al., 2016, Spectral and spatial characterisation of laser-driven positron beams, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 59, ISSN: 0741-3335
Siminos E, Skupin S, Savert A, et al., 2016, Modeling ultrafast shadowgraphy in laser-plasma interaction experiments, Plasma Physics and Controlled Fusion, Vol: 58, ISSN: 1361-6587
Ultrafast shadowgraphy is a new experimental technique that uses few cycle laser pulses to imagedensity gradients in a rapidly evolving plasma. It enables structures that move at speeds close tothe speed of light, such as laser driven wakes, to be visualized. Here we study the process of shadowgraphicimage formation during the propagation of a few cycle probe pulse transversely througha laser-driven wake using three-dimensional particle-in-cell simulations. In order to construct syntheticshadowgrams a near-field snapshot of the ultrashort probe pulse is analyzed by means ofFourier optics, taking into account the effect of a typical imaging setup. By comparing syntheticand experimental shadowgrams we show that the generation of synthetic data is crucial for the correctinterpretation of experiments. Moreover, we study the dependence of synthetic shadowgramson various parameters such as the imaging system aperture, the position of the object plane andthe probe pulse delay, duration and wavelength. Finally, we show that time-dependent informationfrom the interaction can be recovered from a single shot by using a broadband, chirped probe pulseand subsequent spectral filtering.
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