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Journal articleBaggott R, Rose S, Mangles S, 2020,
Calculating opacity in hot, dense matter using second-order electron-photon and two-photon transitions to approximate line broadening
, Physical Review Letters, Vol: 125, Pages: 145002 – 1-145002 – 5, ISSN: 0031-9007Calculations of the opacity of hot, dense matter require models for plasma line broadening. How-ever, the most general theories are too complex to calculate directly and some approximation is inevitably required. The most widely-used approaches focus on the line centre, where a Lorentzian shape is obtained. Here, we demonstrate that in the opposite limit, far from the line centre, the opacity can be expressed in terms of second-order transitions, such as electron-photon and two-photon processes. We suggest that this insight could form the basis for a new approach to improve calculations of opacity in hot, dense matter. Preliminary calculations suggest that this approach could yield increased opacity away from absorption lines.
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Journal articleConsoli F, De Angelis R, Robinson TS, et al., 2019,
Generation of intense quasi-electrostatic fields due to deposition of particles accelerated by petawatt-range laser-matter interactions
, Scientific Reports, Vol: 9, ISSN: 2045-2322We demonstrate here for the first time that charge emitted by laser-target interactions at petawatt peak-powers can be efficiently deposited on a capacitor-collector structure far away from the target and lead to the rapid (tens of nanoseconds) generation of large quasi-static electric fields over wide (tens-of-centimeters scale-length) regions, with intensities much higher than common ElectroMagnetic Pulses (EMPs) generated by the same experiment in the same position. A good agreement was obtained between measurements from a classical field-probe and calculations based on particle-flux measurements from a Thomson spectrometer. Proof-of-principle particle-in-cell simulations reproduced the measurements of field evolution in time, giving a useful insight into the charging process, generation and distribution of fields. The understanding of this charging phenomenon and of the related intense fields, which can reach the MV/m order and in specific configurations might also exceed it, is very important for present and future facilities studying laser-plasma-acceleration and inertial-confinement-fusion, but also for application to the conditioning of accelerated charged-particles, the generation of intense electric and magnetic fields and many other multidisciplinary high-power laser-driven processes.
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Conference paperMcIlvenny A, Doria D, Romagnani L, et al., 2019,
Absolute calibration of microchannel plate detector for carbon ions up to 250 MeV
, 5th International Conference on Frontiers in Diagnostics Technologies, Publisher: IOP PUBLISHING LTD, ISSN: 1748-0221 -
Journal articleKing M, Butler NMH, Wilson R, et al., 2019,
Role of magnetic field evolution on filamentary structure formation in intense laser-foil interactions
, HIGH POWER LASER SCIENCE AND ENGINEERING, Vol: 7, ISSN: 2095-4719 -
Journal articlePapp D, Wood JC, Gruson V, et al., 2018,
Laser wakefield acceleration with high-power, few-cycle mid-IR lasers
, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 909, Pages: 145-148, ISSN: 0168-9002 -
Journal articleWarwick 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: 0168-9002The 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.
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Journal articleBehm 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 -
Journal articleKrushelnick 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 -
Journal articleWood 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: 2045-2322Betatron 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.
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Journal articleSchumaker W, Liang T, Clarke R, et al., 2018,
Making pions with laser light
, NEW JOURNAL OF PHYSICS, Vol: 20, ISSN: 1367-2630 -
Journal articlePoder 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: 2160-3308The 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.
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Journal articleCole 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 -
Journal articleStreeter 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: 0031-9007We 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.
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Journal articleStreeter 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: 1077-3118We 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.
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Journal articleYu JQ, Hu RH, Gong Z, et al., 2018,
The generation of collimated gamma-ray pulse from the interaction between 10 PW laser and a narrow tube target
, APPLIED PHYSICS LETTERS, Vol: 112, ISSN: 0003-6951 -
Journal articleMcGuffey 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 -
Journal articleCole 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: 2160-3308The 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.
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Conference paperSymes 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.
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Journal articleWarwick 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: 0031-9007We 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.
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Journal articlePoder 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: 0741-3335We 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.
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Journal articleRidgers 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 -
Journal articleCowley J, Thornton C, Arran C, et al., 2017,
Excitation and control of plasma wakefields by multiple laser pulses
, Physical Review Letters, Vol: 119, ISSN: 1079-7114We 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.
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Conference paperWalker 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 -
Journal articleMangles 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: 1089-7623Highly 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.
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Journal articleAlejo A, Krygier AG, Ahmed H, et al., 2017,
High flux, beamed neutron sources employing deuteron-rich ion beams from D2O-ice layered targets
, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 59, ISSN: 0741-3335 -
Journal articleRobinson TS, Consoli F, Giltrap S, et al., 2017,
Low-noise time-resolved optical sensing of electromagnetic pulses from petawatt laser-matter interactions
, Scientific Reports, Vol: 7, ISSN: 2045-2322We report on the development and deployment of an optical diagnostic for single-shot measurement of the electric-field components of electromagnetic pulses from high-intensity laser-matter interactions in a high-noise environment. The electro-optic Pockels effect in KDP crystals was used to measure transient electric fields using a geometry easily modifiable for magnetic field detection via Faraday rotation. Using dielectric sensors and an optical fibre-based readout ensures minimal field perturbations compared to conductive probes and greatly limits unwanted electrical pickup between probe and recording system. The device was tested at the Vulcan Petawatt facility with 1020 W cm−2 peak intensities, the first time such a diagnostic has been used in this regime. The probe crystals were located ~1.25 m from target and did not require direct view of the source plasma. The measured signals compare favourably with previously reported studies from Vulcan, in terms of the maximum measured intra-crystal field of 10.9 kV/m, signal duration and detected frequency content which was found to match the interaction chamber’s horizontal-plane fundamental harmonics of 76 and 101 MHz. Methods for improving the diagnostic for future use are also discussed in detail. Orthogonal optical probes offer a low-noise alternative for direct simultaneous measurement of each vector field component.
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Conference paperMartin P, Doria D, Romagnani L, et al., 2017,
Transition to light sail acceleration using ultraintense femtosecond pulses
Presented are results from experimental campaigns undertaken on the Gemini laser system at the Central Laser Facility in the UK. In these experiments amorphous carbon targets ranging in thickness from 10nm to 100nm were irradiated with high contrast 40fs pulses with an intensity up to 1021 W/cm2, for both circular and linear polarisations and the resulting proton and ion spectra compared. Examining the highest energies achieved for a given polarisation and target thickness, allows to identify the transition from TNSA to LS. Observations of the optimal target thickness for ion acceleration are compared to analytical predictions from LS theory, in addition to results from Particle in Cell modelling.
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Journal articleSarri 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 -
Conference paperScullion C, Doria D, Romagnani L, et al., 2016,
Angularly resolved characterization of ion beams from laser-ultrathin foil interactions
, 4th International Conference on Frontiers in Diagnostics Technologies, Publisher: IOP PUBLISHING LTD, ISSN: 1748-0221 -
Conference paperTing A, Hafizi B, Helle M, et al., 2016,
Staging and Laser Acceleration of Ions in Underdense Plasma
, 17th Advanced Accelerator Concepts Workshop (AAC), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
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