22 results found
Behm K, Hussein AE, Zhao TZ, et al., 2020, Demonstration of femtosecond broadband X-rays from laser wakefield acceleration as a source for pump-probe X-ray absorption studies, High Energy Density Physics, Vol: 35, Pages: 1-5, ISSN: 1574-1818
We present X-ray absorption measurements near the K-edge of laser heated aluminum in a pump-probe configuration using X-rays generated in a laser wakefield accelerator. A 30 fs duration laser pulse from the Herculeslaser system was split into two beamlines, with one used to heat a 4 µm thickness Al foil and the second to drive a laser wakefield accelerator. The laser-heated plasma was probed at various pump-probe delays using the femtosecond duration X-rays generated by betatron oscillations of the electrons in the wakefield. We observe an apparent blue-shift of the K-edge occurring on a sub-picosecond timescale in the transmission spectra.
Bailie D, Hyland C, Singh R, et al., 2020, An investigation of the L-shell X-ray conversion efficiency for laser-irradiated tin foils, Plasma Science and Technology, Vol: 22, Pages: 1-7, ISSN: 1009-0630
We have used the Shenguang II laser in third harmonic (351 nm) to investigate the emission ofL-shell radiation in the 3.3 to 4.4 keV range generated using thin foils of Sn coated onto a parylenesubstrate with irradiation of order 1015 Wcm−2 and nanosecond pulse duration. In our experiment,we have concentrated on assessing the emission on the non-laser irradiated side as this allows anexperimental geometry relevant to experiments on photo-ionised plasmas where a secondary targetmust be placed close to the source, to achieve X-ray fluxes appropriate to astrophysical objects.Overall L-shell conversion efficiencies are estimated to be of order 1%, with little dependence onSn thickness between 400 and 800 nm.
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.
White S, Irwin R, Warwick R, et al., 2018, Production of photoionized plasmas in the laboratory using X-ray line radiation, Physical Review E, Vol: 97, ISSN: 1539-3755
In this paper we report the experimental implementation of a theoretically proposed technique for creating a photoionized plasma in the laboratory using x-ray line radiation. Using a Sn laser plasma to irradiate an Ar gas target, the photoionization parameter, ξ=4πF/Ne, reached values of order 50ergcms−1, where F is the radiation flux in ergcm−2s−1. The significance of this is that this technique allows us to mimic effective spectral radiation temperatures in excess of 1 keV. We show that our plasma starts to be collisionally dominated before the peak of the x-ray drive. However, the technique is extendable to higher-energy laser systems to create plasmas with parameters relevant to benchmarking codes used to model astrophysical objects.
Hill EG, Perez-Callejo G, Rose SJ, 2018, ALICE: A non-LTE plasma atomic physics, kinetics and lineshape code, High Energy Density Physics, Vol: 26, Pages: 56-67, ISSN: 1574-1818
All three parts of an atomic physics, atomic kinetics and lineshape code, ALICE, are described. Examples of the code being used to model the emissivity and opacity of plasmas are discussed and interesting features of the code which build on the existing corpus of models are shown throughout.
Hoarty DJ, Sircombe N, Beiersdorfer P, et al., 2017, Modelling K shell spectra from short pulse heated buried microdot targets, High Energy Density Physics, Vol: 23, Pages: 178-183, ISSN: 1574-1818
K shell X-ray emission measurements have been used to diagnose plasma conditions in short-pulse heated buried microdot targets on the Orion high power laser. These experiments have been used to validate simulations of short pulse laser-solid interaction that combine hybrid PIC modelling of the laser absorption with radiation-hydrodynamics simulations including an electron transport model. Comparison of these simulations with streaked K shell spectroscopy show the importance of including radial gradients in fitting the spectra. An example is presented of the emission of sulphur from a 50 µm diameter microdot sample buried in a plastic foil. Previously agreement between simulation and experiment was obtained only by treating the absorbed energy, electron temperature and beam divergence as fitting parameters. The good agreement obtained in this work used the measured laser energy and laser pulse length and calculated the laser-solid target interaction from first principles.
Hoarty DJ, Hill EG, Beiersdorfer P, et al., 2017, Measurements of plasma spectra from hot dense elements and mixtures at conditions relevant to the solar radiative zone, AIP Conference Proceedings, Vol: 1811, ISSN: 1551-7616
X-ray emission spectroscopy has been used to study hot dense plasmas produced using high power laser irradiation of dot samples buried in low Z foils of plastic or diamond. By combining a high contrast short pulse (picosecond timescale) laser beam operating in second harmonic with long pulse (nanosecond timescale) laser beams in third harmonic, and with pulse shaping of the long pulse beams, a range of plasma temperatures from 400eV up to 2.5keV and electron densities from 5e22 up to 1e24/cc have been accessed. Examples are given of measurements of dense plasma effects such as ionization potential depression and line-broadening from the K-shell emission spectra of a range of low Z elements and mixtures and compared to model prediction. Detailed spectra from measurements of the L-shell emission from mid-Z elements are also presented for an example spectrum of germanium. These data are at conditions found in stellar interiors and in particular in the radiative zone of the sun. The plasma conditions are inferred from comparison of the measured spectra to detailed modeling using atomic kinetics and spectral synthesis codes.
Beiersdorfer P, Brown GV, Shepherd R, et al., 2016, Lineshape measurements of He-beta spectra on the ORION laser facility, PHYSICS OF PLASMAS, Vol: 23, ISSN: 1070-664X
Hill EG, 2016, Solving an age-old riddle: Can inertial confinement finally deliver fusion?, Angle Journal, Vol: 2016
Sherlock, Hill EG, Evans, et al., 2014, In-depth Plasma-Wave Heating of Dense Plasma Irradiated by Short Laser Pulses, Physical Review Letters, Vol: 113, ISSN: 1079-7114
Hill EG, Rose SJ, 2014, Non-thermal enhancement of electron-positron pair creation in burning thermonuclear laboratory plasmas, High Energy Density Physics
The ability to create matter from light is amongst the most striking predictions of quantum electrodynamics. Experimental signatures of this have been reported in the scattering of ultra-relativistic electron beams with laser beams1,2, intense laser–plasma interactions3 and laser-driven solid target scattering4. However, all such routes involve massive particles. The simplest mechanism by which pure light can be transformed into matter, Breit–Wheeler pair production (γγ′ → e+e−)5, has never been observed in the laboratory. Here, we present the design of a new class of photon–photon collider in which a gamma-ray beam is fired into the high-temperature radiation field of a laser-heated hohlraum. Matching experimental parameters to current-generation facilities, Monte Carlo simulations suggest that this scheme is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot. This would provide the first realization of a pure photon–photon collider, representing the advent of a new type of high-energy physics experiment.
Hill EG, 2014, Calculation of unit tensor operators using a restricted set of Slater determinants, JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, Vol: 140, Pages: 1-6, ISSN: 0022-4073
Hill EG, 2014, Fractional parentage coefficients using a restricted set of slater determinants, Journal of Quantitative Spectroscopy and Radiative Transfer, Vol: 147, Pages: 71-78
Sherlock M, Hill EG, Rose SJ, 2013, Kinetic simulations of the heating of solid density plasma by femtosecond laser pulses, HIGH ENERGY DENSITY PHYSICS, Vol: 9, Pages: 38-41, ISSN: 1574-1818
Hill EG, Rose SJ, 2012, Modelling of Silicon in inertial confinement fusion conditions, HIGH ENERGY DENSITY PHYSICS, Vol: 8, Pages: 307-312, ISSN: 1574-1818
Hill EG, Rose SJ, 2012, Thomson scattering in short pulse laser experiments, PHYSICS OF PLASMAS, Vol: 19, ISSN: 1070-664X
Hill EG, Rose SJ, 2011, Alternative methods of producing photoionised plasmas in the laboratory, HIGH ENERGY DENSITY PHYSICS, Vol: 7, Pages: 377-382, ISSN: 1574-1818
Hill EG, 2011, Non-LTE Plasma Spectroscopy
This thesis is based around the techniques used in theoretical and computational modellingof the spectra and radiative properties of non-LTE plasmas, particularly those which are photoionised.The thesis begins with a discussion of the concepts important to the modelling of these plasmas,and of the methods which are used in order to model them. Within this, the DCA code ALICE isdescribed in the context of a general discussion of collisional-radiative models. The code is thenapplied to the modelling of a laboratory photoionised astrophysical plasma experiment, and therelation of the experiment to astrophysical plasmas is discussed. A new experiment in that fieldis then proposed and the increased relevance of the new method to the astrophysical case isdemonstrated. Throughout the application of the code, several problems with the use of DCAcodes to model plasmas are discussed, and therefore the design of a new DTA code is described,some of the methods used within which are novel. The new code is designed to consider highdensity plasmas where the shapes of spectral lines are important and a description of linebroadening theory is given. This code is applied to the first analysis of a recently performedlaser-plasma experiment. The thesis concludes with a discussion of spectra of Germaniumobtained from NIF, and some possible unusual features contained within them.
Hill E, Rose S, 2010, Photoionized astrophysical plasmas in the laboratory, PHYSICS OF PLASMAS, Vol: 17, ISSN: 1070-664X
Hill EG, Rose SJ, 2009, Modelling photoionised plasma experiments, High Energy Density Physics, Vol: 5
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