Fast electron transport patterns in intense laser-irradiated solids diagnosed by modeling measured multi-MeV proton beams

MacLellan, D. A.; Carroll, D. C.; Gray, R. J.; Booth, N.; Gonzalez-Izquierdo, Bruno; Powell, H.; Scott, Graeme; Neely, D.; McKenna, P.

doi:10.1017/s0263034613000529

Cited by 8 publications

(16 citation statements)

References 17 publications

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“…To quantify the degree of filamentation within the beam, the method used by MacLellan et al [8] is employed, where the mean coefficient of variation, C M P , represents as a percentage, the radially averaged standard deviation in proton dose divided by the radially averaged dose. This measurement allows the degree of disorder in the beam to be quantified as a function of its radius, and as we find this to be quasi-constant, we take the average value of this function, C M P , to represent the degree of disorder in the beam measured at a given proton energy.…”

Section: Resultsmentioning

confidence: 99%

“…Extensive numerical modelling and experimental studies have led to a powerfully predictive 3D hybrid model showing that low temperature plasma (10-100 eV) resistivity gradients can lead to filamentation of the electron beam [5][6][7]. Using the final electron distribution at the target rear, a sheath expansion model [8] has been shown to accurately forecast the subsequently accelerated proton distribution, and this work established a precedent for using the accelerated proton beam spatial distribution as a diagnostic of fast electron transport physics within the target.…”

Section: Introductionmentioning

confidence: 99%

“…The dose maps retrieved for 6.5 MeV protons, as measured on the RCF stack, from interactions with (a) 45μm graphite foils (b) 5-25 μm gold foils, at a series of time delays between the pulses. (c) The layer averaged mean coefficient of variation as derived from[8] is shown for the two data sets, as a quantitative measure of the observed structure.…”

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confidence: 99%

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Diagnosis of Weibel instability evolution in the rear surface density scale lengths of laser solid interactions via proton acceleration

et al. 2017

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It is shown for the first time that the spatial and temporal distribution of laser accelerated protons can be used as a diagnostic of Weibel instability presence and evolution in the rear surface scale lengths of a solid density target. Numerical modelling shows that when a fast electron beam is injected into a decreasing density gradient on the target rear side, a magnetic instability is seeded with an evolution which is strongly dependent on the density scale length. This is manifested in the acceleration of a filamented proton beam, where the degree of filamentation is also found to be dependent on the target rear scale length. Furthermore, the energy dependent spatial distribution of the accelerated proton beam is shown to provide information on the instability evolution on the picosecond timescale over which the protons are accelerated. Experimentally, this is investigated by using a controlled prepulse to introduce a target rear scale length, which is varied by altering the time delay with respect to the main pulse, and similar trends are measured. This work is particularly pertinent to applications using laser pulse durations of tens of picoseconds, or where a micron level density scale length is present on the rear of a solid target, such as proton-driven fast ignition, as the resultant instability may affect the uniformity of fuel energy coupling. 1 2 or » FWTM 1.8 FWHM. The quoted time delay can therefore be considered to be a sample of the intensity profile of a shorter duration FWHM pulse.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diagnosis of Weibel instability evolution in the rear surface density scale lengths of laser solid interactions via proton acceleration

et al. 2017

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“…Given that the design of FI targets is strongly inluenced by experimental results and that electron transport codes are benchmarked using these results, it is important to determine to what extent low temperature effects inluence fast electron transport in solids. Through experimentally and numerically investigating electron transport in silicon and different forms of carbon, we have recently shown that the electrical resistivity of a material at temperatures as low as a few eV plays a deining role in the evolution of resistive magnetic ields (B-ields) and thus the fast electron transport physics [10][11][12]. A picosecond pulse of fast electrons (driven by a picosecond-duration laser pulse) traverses a few hundred-micron-thick target on a timescale in which the background electrons are hot, but the ions are still relatively cold and temporarily retain their lattice structure.…”

Section: Introductionmentioning

confidence: 99%

Influence of low-temperature resistivity on fast electron transport in solids: scaling to fast ignition electron beam parameters

McKenna

MacLellan

Butler

et al. 2015

Plasma Phys. Control. Fusion

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This version is available at https://strathprints.strath.ac.uk/50862/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. © 2015 IOP Publishing Ltd Printed in the UK IntroductionControlling the transport of large (multi-mega-Ampere) currents of fast electrons in dense plasma is important for the many applications of high power laser-solid interactions, including ion acceleration [1, 2] and radiation production [3,4]. It is also important for the development of the fast ignition (FI) approach to inertial coninement fusion (ICF) [5] in which fast electrons are used to transfer energy from an 'ignition' laser pulse to the compressed Deuterium-Tritium (D-T) fusion fuel. In this scheme, an electron current of the order of giga-Amperes is required to propagate over a distance of 100-200 µm from its source to ignite the compressed fuel. In FI schemes involving a hollow cone (to enable propagation of the ignition laser pulse closer to the compressed fuel) the electrons also propagate through the end wall of the solid-density cone, which is typically 100 µm from the centre of the fuel [6]. The mean electron energy is bound by the requirements for it to be high enough such that the electrons are not subject to extensive scattering losses and low enough that eficient energy deposition occurs in the hot spot. This in turns sets the peak intensity of the ignition laser pulse to the 10 20 Wcm −2 range, as determined by ponderomotive scaling [7]. The energy of the ignition laser pulse depends not only on the ignition physics, but also on the laser-to-electron energy conversion eficiency and the fast electron transport physics. Reduction of the divergence of the electron beam and the minimisation of transport instabilities leading to energy losses (via Ohmic heating) is important to lower the energy requirements of the ignition laser pulse. The development of radically different beam transport patterns, such as 'annular' beams, can also help to achi...

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“…Figures 5(c) and 5(f) correspond to the calculated proton beam profiles, as obtained by mapping the fast electron density maps at the target rear surface into E-field distributions and, subsequently, into an expanding proton front. The principles behind this approach are outlined in [17], and the present modeling takes account of the evolution of the electron density distribution at the target rear. The final proton beam distributions resulting from the fast electron transport simulation results are in good qualitative agreement with the experiment results in Fig.…”

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confidence: 99%

Tunable Mega-Ampere Electron Current Propagation in Solids by Dynamic Control of Lattice Melt

et al. 2014

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The influence of lattice-melt-induced resistivity gradients on the transport of mega-ampere currents of fast electrons in solids is investigated numerically and experimentally using laser-accelerated protons to induce isochoric heating. Tailoring the heating profile enables the resistive magnetic fields which strongly influence the current propagation to be manipulated. This tunable laser-driven process enables important fast electron beam properties, including the beam divergence, profile, and symmetry to be actively tailored, and without recourse to complex target manufacture.

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Fast electron transport patterns in intense laser-irradiated solids diagnosed by modeling measured multi-MeV proton beams

Cited by 8 publications

References 17 publications

Diagnosis of Weibel instability evolution in the rear surface density scale lengths of laser solid interactions via proton acceleration

Diagnosis of Weibel instability evolution in the rear surface density scale lengths of laser solid interactions via proton acceleration

Influence of low-temperature resistivity on fast electron transport in solids: scaling to fast ignition electron beam parameters

Tunable Mega-Ampere Electron Current Propagation in Solids by Dynamic Control of Lattice Melt

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