ORCID Profile
0000-0002-8581-4307
Current Organisation
James Cook University
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Publisher: IOP Publishing
Date: 30-04-2012
Publisher: IOP Publishing
Date: 27-01-2017
Publisher: American Physical Society (APS)
Date: 16-04-2015
Publisher: American Physical Society (APS)
Date: 27-05-2015
Publisher: IOP Publishing
Date: 15-03-2017
Publisher: American Physical Society (APS)
Date: 07-11-2018
Publisher: American Physical Society (APS)
Date: 16-07-2021
Publisher: American Physical Society (APS)
Date: 29-03-2019
Publisher: American Physical Society (APS)
Date: 06-01-2021
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.APRADISO.2013.01.008
Abstract: We present a study of electron and positron transport in water in both the gaseous and liquid states using a Boltzmann equation analysis and a Monte-Carlo simulation technique. We assess the importance of coherent scattering processes when considering transport of electrons ositrons in dense gases and liquids. We highlight the importance of electron and positron swarm studies and experiments as a test of the accuracy and completeness of cross-sections, as well as a technique for benchmarking Monte-Carlo simulations. The thermalization of low-energy positrons (<150 eV) in water is discussed and the sensitivity of the profiles to the form of the cross-sections in this energy region, and assumptions in the microscopic processes, is considered.
Publisher: IOP Publishing
Date: 02-08-2016
Publisher: IOP Publishing
Date: 12-03-2019
Publisher: AIP Publishing
Date: 05-08-2019
DOI: 10.1063/1.5108619
Abstract: The pulsed Townsend technique has been used to measure transport coefficients in mixtures of tetrahydrofuran (THF) with N2 and argon. These measurements are the first investigations of swarm transport in gas mixtures with THF, with the drift velocity and effective Townsend ionization coefficient reported for a range of reduced electric fields between 0.23 and 800 Td (1 Td = 10−21 V m2). These transport coefficients are compared with those calculated using a multiterm kinetic theory, using the cross section set developed in our previous studies [N. A. Garland et al., Phys. Rev. A 88, 062712 (2013) and M. J. E. Casey et al., J. Chem. Phys. 147, 195103 (2017)]. The swarm technique of iteratively adjusting cross sections to reproduce experimental transport measurements is subsequently utilized in this study to address the deficiencies in the earlier cross section sets, exposed by the gas mixture measurements. Refinement of the low-energy extrapolation of the quasielastic database cross section and the low-energy extrapolation and magnitude of the dissociative electron attachment cross section are detailed, as well as the adjustments to the two previously proposed neutral dissociation cross sections. These refinements were necessary in order to minimize differences between our measured and calculated transport coefficients.
Publisher: IAIN Samarinda
Date: 19-05-2017
Abstract: The aim of this paper is to explore the challenges to, and benefits of, fostering of critical thinking (CT) in the Saudi EFL (English as a foreign language) context. In the next section, the concept of CT will be clarified. In the following two sections, possible challenges or barriers to CT, whether religious or pedagogical, in the Saudi context are analyzed and refuted. After discussing the religious and the educational background of this issue, practices for promoting CT inside EFL classrooms are described. Finally, the benefits of incorporating CT strategies into language learning are outlined.
Publisher: Springer Science and Business Media LLC
Date: 02-03-2022
DOI: 10.1038/S41586-021-04348-8
Abstract: The interaction of intense particle bunches with plasma can give rise to plasma wakes 1,2 capable of sustaining gigavolt-per-metre electric fields 3,4 , which are orders of magnitude higher than provided by state-of-the-art radio-frequency technology 5 . Plasma wakefields can, therefore, strongly accelerate charged particles and offer the opportunity to reach higher particle energies with smaller and hence more widely available accelerator facilities. However, the luminosity and brilliance demands of high-energy physics and photon science require particle bunches to be accelerated at repetition rates of thousands or even millions per second, which are orders of magnitude higher than demonstrated with plasma-wakefield technology 6,7 . Here we investigate the upper limit on repetition rates of beam-driven plasma accelerators by measuring the time it takes for the plasma to recover to its initial state after perturbation by a wakefield. The many-nanosecond-level recovery time measured establishes the in-principle attainability of megahertz rates of acceleration in plasmas. The experimental signatures of the perturbation are well described by simulations of a temporally evolving parabolic ion channel, transferring energy from the collapsing wake to the surrounding media. This result establishes that plasma-wakefield modules could be developed as feasible high-repetition-rate energy boosters at current and future particle-physics and photon-science facilities.
Publisher: The Royal Society
Date: 24-06-2019
Abstract: The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2018
Publisher: American Physical Society (APS)
Date: 07-12-2018
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2018
Publisher: American Physical Society (APS)
Date: 18-08-2023
Publisher: IOP Publishing
Date: 09-10-2020
Abstract: In previous papers we have proposed a method for the ab initio calculation of fully differential cross-sections for electron scattering in liquids and applied it to liquid argon, xenon and krypton. In this paper, we extend the procedure to the consideration of positron scattering in liquid helium, which is complicated by the annihilation process as well as the fact that the electron definition for the region ‘owned’ by a target atom used previously does not have a positron analogue. We explore several physically motivated definitions to obtain effective positron scattering in the dense fluid. We find that our calculations of a pure helium system cannot precisely match experimental measurements, however by including a small admixture ( .1%) of an impurity, we can obtain reasonable agreement in the dense gas phase. In contrast, the comparison between our calculations and liquid phase measurements is less satisfactory. This provides motivation to explore further multiple scattering effects in the theory.
Publisher: Springer Science and Business Media LLC
Date: 08-01-2021
DOI: 10.1038/S41467-020-20676-1
Abstract: A Correction to this paper has been published: 0.1038/s41467-020-20676-1
Publisher: American Physical Society (APS)
Date: 28-02-2014
Publisher: AIP Publishing
Date: 2021
DOI: 10.1063/5.0021117
Abstract: Precise characterization and tailoring of the spatial and temporal evolution of plasma density within plasma sources are critical for realizing high-quality accelerated beams in plasma wakefield accelerators. The simultaneous use of two independent diagnostics allowed the temporally and spatially resolved detection of plasma density with unprecedented sensitivity and enabled the characterization of the plasma temperature in discharge capillaries for times later than 0.5 µs after the initiation of the discharge, at which point the plasma is at local thermodynamic equilibrium. A common-path two-color laser interferometer for obtaining the average plasma density with a sensitivity of 2 × 1015 cm−2 was developed together with a plasma emission spectrometer for analyzing spectral line broadening profiles with a resolution of 5 × 1015 cm−3. Both diagnostics show good agreement when applying the spectral line broadening analysis methodology of Gigosos and Cardeñoso in the temperature range of 0.5 eV–5.0 eV. For plasma with densities of 0.5–2.5 × 1017 cm−3, temperatures of 1 eV–7 eV were indirectly measured by combining the diagnostic information. Measured longitudinally resolved plasma density profiles exhibit a clear temporal evolution from an initial flat-top to a Gaussian-like shape in the first microseconds as material is ejected out from the capillary. These measurements pave the way for highly detailed parameter tuning in plasma sources for particle accelerators and beam optics.
Publisher: IOP Publishing
Date: 05-08-2014
Publisher: AIP Publishing
Date: 11-07-2023
DOI: 10.1063/5.0153973
Abstract: Seminal gas discharge experiments of the late 19th and early 20th centuries laid the foundations of modern physics, and the influence of this “golden era” continues to resonate well into the 21st century through modern technologies, medical applications, and fundamental scientific investigations. Key to this continuing success story has been the kinetic equation formulated by Ludwig Boltzmann in 1872, which provides the theoretical foundations necessary for analyzing such highly non-equilibrium situations. However, as discussed here, the full potential of Boltzmann’s equation has been realized only in the past 50 years or so, with modern computing power and analytical techniques facilitating accurate solutions for various types of charged particles (ions, electrons, positrons, and muons) in gases. Our ex le of thermalization of electrons in xenon gas highlights the need for such accurate methods—the traditional Lorentz approximation is shown to be hopelessly inadequate. We then discuss the emerging role of Boltzmann’s equation in determining cross sections by inverting measured swarm experiment transport coefficient data using machine learning with artificial neural networks.
Publisher: AIP Publishing
Date: 20-11-2017
DOI: 10.1063/1.5004717
Abstract: The drift velocity and first Townsend ionization coefficient of electrons in gaseous tetrahydrofuran are measured over the range of reduced electric fields 4-1000 Td using a pulsed-Townsend technique. The measured drift velocities and Townsend ionization coefficients are subsequently used, in conjunction with a multi-term Boltzmann equation analysis, as a further discriminative assessment on the accuracy and completeness of a recently proposed set of electron-THF vapor cross sections. In addition, the sensitivity of the transport coefficients to uncertainties in the existing cross sections is presented. As a result of that analysis, a refinement of the momentum transfer cross section for electron-THF scattering is presented, along with modifications to the neutral dissociation and dissociative electron attachment cross sections. With these changes to the cross section database, we find relatively good self-consistency between the measured and simulated drift velocities and Townsend coefficients.
Publisher: IOP Publishing
Date: 2011
Publisher: Springer Science and Business Media LLC
Date: 25-11-2020
DOI: 10.1038/S41467-020-19811-9
Abstract: Plasma-wakefield accelerators driven by intense particle beams promise to significantly reduce the size of future high-energy facilities. Such applications require particle beams with a well-controlled energy spectrum, which necessitates detailed tailoring of the plasma wakefield. Precise measurements of the effective wakefield structure are therefore essential for optimising the acceleration process. Here we propose and demonstrate such a measurement technique that enables femtosecond-level (15 fs) s ling of longitudinal electric fields of order gigavolts-per-meter (0.8 GV m −1 ). This method—based on energy collimation of the incoming bunch—made it possible to investigate the effect of beam and plasma parameters on the beam-loaded longitudinally integrated plasma wakefield, showing good agreement with particle-in-cell simulations. These results open the door to high-quality operation of future plasma accelerators through precise control of the acceleration process.
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2018
Publisher: American Physical Society (APS)
Date: 29-12-2021
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2019
Publisher: IOP Publishing
Date: 14-06-2017
Publisher: IOP Publishing
Date: 15-10-2018
Publisher: IOP Publishing
Date: 15-05-2018
Publisher: AIP Publishing
Date: 20-04-2015
DOI: 10.1063/1.4917258
Abstract: The transport of excess electrons in liquid argon driven out of equilibrium by an applied electric field is revisited using a multi-term solution of Boltzmann’s equation together with ab initio liquid phase cross-sections calculated using the Dirac-Fock scattering equations. The calculation of liquid phase cross-sections extends previous treatments to consider multipole polarisabilities and a non-local treatment of exchange, while the accuracy of the electron-argon potential is validated through comparison of the calculated gas phase cross-sections with experiment. The results presented highlight the inadequacy of local treatments of exchange that are commonly used in liquid and cluster phase cross-section calculations. The multi-term Boltzmann equation framework accounting for coherent scattering enables the inclusion of the full anisotropy in the differential cross-section arising from the interaction and the structure factor, without an a priori assumption of quasi-isotropy in the velocity distribution function. The model, which contains no free parameters and accounts for both coherent scattering and liquid phase screening effects, was found to reproduce well the experimental drift velocities and characteristic energies.
Publisher: IOP Publishing
Date: 14-02-2018
Publisher: IOP Publishing
Date: 08-11-2019
No related grants have been discovered for Gregory Boyle.