Papers by Rebecca Seviour
2020 IEEE International Conference on Plasma Science (ICOPS), Dec 6, 2020
We present our current progress towards the development of novel RF sources that utilize low loss... more We present our current progress towards the development of novel RF sources that utilize low loss, dispersion engineered, artificial materials. The frequency dispersive artificial media were designed to reduce EM wave propagation to approximately 0.2 c, facilitating interaction with a 20 keV electron beam. The artificial media were tailored to yield specific constituitive parameters that were determined via a variation of the Nicolson Ross Weir based parameter retrieval technique adapted by Smith et al1.
IEEE Transactions on Plasma Science, Oct 1, 2022
HIS special issue of the IEEE TRANSACTIONS ON PLASMA SCIENCE (TPS) mainly contains works presente... more HIS special issue of the IEEE TRANSACTIONS ON PLASMA SCIENCE (TPS) mainly contains works presented at the 23rd IEEE Pulsed Power Conference (PPC) held between December 12-16, 2021 (https://uta.engineering/ ppcsofe2021). The conference was jointly held with the 29th IEEE Symposium on Fusion Engineering (SOFE). Each respective conference has a long history of serving their community as gathering forums for the presentation and discussion of their field's research topics. Originally planned to be held in Denver, CO, USA, the conference was changed to a virtual-only format due to COVID-19 restrictions. Even with the virtual-only format, the 23rd PPC was extremely successful with 289 quality papers submitted from 22 countries from America, Europe, and Asia. This Special Issue covers the following range of topics that were also the focus areas of PPC 2021: 1) HV Insulation and Breakdown 2) Opening and Closing Switches 3) High Power Microwave Systems and Sources 4) High Current Accelerators 5) LTDs, PFLs, and Transformers 6) Numerical Modeling and Computational Techniques 7) Fusion and Z-Pinches 8) High-Energy Density Physics and Technology 9) Intense Electron and Ion Beams & Ion and Electron Sources 10) Pulsed Power Diagnostics 11) Medical, Industrial, and Commercial Applications 12) Explosive Pulsed Power 13) High-Power Electronics 14) Electromagnetic Launch As many special issues have in the past, this Special Issue chronicles the latest advances in Pulsed Power Science and Technology (PPST). A total of 20 contributed, peer-reviewed articles are presented in this Special Issue. These articles are distributed between electromagnetic launch, pulsed power physics and components, HV insulation, and high-power microwaves. The reader will note international participation in the contributed articles. Similarly, there is also diversity within the constituent scientific community as reflected in the originating institutions that encompass universities, industry, and government laboratories.
IEEE Transactions on Plasma Science, 2010
At CERN a compact Quadrupole Resonator has been developed for the RF characterization of supercon... more At CERN a compact Quadrupole Resonator has been developed for the RF characterization of superconducting samples at different frequencies. In this contribution measurements on bulk niobium and niobium film on copper samples are presented. Surface resistance results are being correlated to surface analyses measurements carried out on the same samples.
2022 IEEE International Conference on Plasma Science (ICOPS)
The International Design Study for the Neutrino Factory (the IDS-NF) was established by the commu... more The International Design Study for the Neutrino Factory (the IDS-NF) was established by the community at the ninth 'International Workshop on Neutrino Factories, super-beams, and beta- beams' which was held in Okayama in August 2007. The IDS-NF mandate is to deliver the Reference Design Report (RDR) for the facility on the timescale of 2012/13. In addition, the mandate for the study [3] requires an Interim Design Report to be delivered midway through the project as a step on the way to the RDR. This document, the IDR, has two functions: it marks the point in the IDS-NF at which the emphasis turns to the engineering studies required to deliver the RDR and it documents baseline concepts for the accelerator complex, the neutrino detectors, and the instrumentation systems. The IDS-NF is, in essence, a site-independent study. Example sites, CERN, FNAL, and RAL, have been identified to allow site-specific issues to be addressed in the cost analysis that will be presented in the RDR. The choice of example sites should not be interpreted as implying a preferred choice of site for the facility.
In this paper we examine the effect of introducing an Electromagnetic metamaterial into a Travell... more In this paper we examine the effect of introducing an Electromagnetic metamaterial into a Travelling Wave structure to mediate inverse Cherenkov acceleration. Electromagnetic metamaterials are artificial materials that consist of macroscopic structures that yield an effective permittivity and permeability less than zero. The properties of metamaterials are highly frequency dependent and give rise to very novel dispersion relationships. We show that the introduction of a specifically designed metamaterial into the interaction region gives rise to a novel dispersion curve yielding a unique wave-particle interaction. We demonstrate that this novel wave-particle interaction gives rise energy exchange from wave to beam over an extended interaction regime. We also discuss the benefits and issues that arise from having a metamaterial in a high vacuum high power environment with a specific focus on the issue of loss in metamaterial structures.
Journal of Atmospheric and Solar-Terrestrial Physics, 2018
Intense electromagnetic pulses interacting with a plasma can create a wake of plasma oscillations... more Intense electromagnetic pulses interacting with a plasma can create a wake of plasma oscillations. Electrons trapped in such oscillations can be accelerated under certain conditions to very high energies. We study the optimal conditions for the wakefield acceleration to produce MeV electrons in planetary plasmas under collisionless conditions. The conditions for the optimal plasma densities can be found in the Earth atmosphere at higher altitudes than 10-15 km, which are the altitudes where lightning leaders can take place.
Journal of Applied Physics, Sep 28, 2022
Electron emission into a nanogap is not instantaneous, which presents a difficulty in simulating ... more Electron emission into a nanogap is not instantaneous, which presents a difficulty in simulating ultra-fast behavior using particle models. A method of approximating the transmission and reflection delay (TARD) times of a wave packet interacting with barriers described by a delta function, a metal-insulator-metal (MIM, rectangular) barrier, and a Fowler Nordheim (FN, triangular) barrier is given, and has application to simulation. It is based on the superposition of a finite number of exact basis states obtained from Schrödinger's equation, analogous to how quantum carpets are simulated. As a result, it can exactly and uniquely follow exponentially small tunneling currents. A Bohm-like trajectory is obtained from the time evolution of the density: it shows delay in both the transmitted and reflected packets that can be simply evaluated. The relations to prior studies of the analytic δ-function barrier and the Wigner distribution function (WDF) methods are described. A comparison of the TARD times is contrasted to alternate times in the Büttiker-Landauer (BL) and McColl-Hartman (MH) times; the MH approach is further reformulated explicitly in terms of Gamow factors to consider how the McColl-Hartman effect is to be related, particularly in the case of the FN barrier of field emission.
The ever-growing demand for higher RF gradients has considerably increased the risk of breakdown ... more The ever-growing demand for higher RF gradients has considerably increased the risk of breakdown in accelerating structures. Field emission is the most common form of RF breakdown that generates free electrons capable of inflicting irreversible damages on the RF surface. This paper presents a systematic experimental and simulation programme to understand possible sources and their influence on RF cavity operation.
High Power Microwave Sources and Technologies Using Metamaterials
In this paper we present the design for a low-cost RF cavity capable of accelerating protons from... more In this paper we present the design for a low-cost RF cavity capable of accelerating protons from 100 keV to 1 MeV. The system is designed to meet the specifications from the proposed Alceli LTD medical proton therapy linac, to deliver a 1 nA proton beam current with a 1 kHz repetition rate. We present a design of an RF normal conducting (NC) re-entrant Cu cavity operating at 40MHz consisting of a coupled two cavity system, both driven by a single Marx generator. The choice of such a low operating frequency for the cavity system enables us to use a relatively low-cost cost Marx Generator as the RF source. Marx generators work in a similar fashion to a Cockcroft-Walton accelerator (without the expensive components), creating a high-voltage pulse by charging a number of capacitors relatively slowly in parallel, then rapidly discharging in series, via spark gaps. Marx generators can deliver 2.5GW, 1 ns pulses, with rise times of 200 ps, and (relatively) low jitter.
2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), Aug 1, 2017
Since their first realization the development of metamaterial based devices and applications has ... more Since their first realization the development of metamaterial based devices and applications has gained an increasing level of interest. These materials offer the opportunity to specifically engineer the materials ability to, control, enhance and suppress EM wave propagation though and near these materials, either in a specific direction or altogether. These materials have been used to construct a range of novel microwave devices such as antennas [1,2], phase-shifters [3], couplers [4], broadband compact power-dividers [5] and other devices such as beam steerers, modulators, band-pass filters and lenses. More recently researchers have considered the use of metamaterials for MIMO application, either as antenna or parasitic/absorptive elements to control interference. In this paper we present an overview of metamaterials, looking at design, fabrication, and characterization. Focused towards the ability of metamaterials to offer a tailored EM mm-wave response for novel MIMO and 5G applications.
Journal of Applied Physics
In this paper, we introduce the theoretical framework underlying our proposed methodology of veri... more In this paper, we introduce the theoretical framework underlying our proposed methodology of verification and validation (V&V) for quantum mechanical emission models using analogous macroscopic electromagnetic systems. We derive the correspondence between quantum mechanics and electromagnetism using the transfer matrix approach and describe the electromagnetic analog that will be used to anchor the atomistic quantum tunneling simulations. Finally, we illustrate this correspondence by comparing the quantum mechanical and electromagnetic systems for some simple, analytically soluble examples and outline future V&V work based on the framework presented here.
Journal of Applied Physics, 2022
In this paper, we introduce the theoretical framework underlying our proposed methodology of veri... more In this paper, we introduce the theoretical framework underlying our proposed methodology of verification and validation (V&V) for quantum mechanical emission models using analogous macroscopic electromagnetic systems. We derive the correspondence between quantum mechanics and electromagnetism using the transfer matrix approach, and describe the electromagnetic analog that will be used to anchor the atomistic quantum tunneling simulations. Finally, we illustrate this correspondence by comparing the quantum mechanical and electromagnetic systems for some simple, analytically soluble examples and outline future V&V work based on the framework presented here.
A low energy Fixed Field Alternating Gradient (FFAG) accelerator has been designed for the produc... more A low energy Fixed Field Alternating Gradient (FFAG) accelerator has been designed for the production of radioisotopes. Tracking studies have been conducted using the OPAL code [1], including the effects of space charge. Radioisotopes have a wide range of uses in medicine, and recent disruption to the supply chain has seen a renewed effort to find alternative isotopes and production methods. The design features separate sector magnets with non-scaling, non-linear field gradients but without the counter bends commonly found in FFAG’s. The machine is isochronous at the level of 0.3 % up to at least 28 MeV and hence able to operate in Continuous Wave (CW) mode. Both protons and helium ions can be used with this design and it has been demonstrated that proton beams with currents of up to 20 mA can be accelerated. An interesting option for the production of radioisotopes is the use of a thin internal target. We have shown that this design has large acceptance, ideal for allowing the beam...
A non-scaling fixed field alternating gradient (nsFFAG) accelerator is being designed for helium ... more A non-scaling fixed field alternating gradient (nsFFAG) accelerator is being designed for helium ion therapy. This facility will consist of 2 nested rings, treating with helium ions (He) and image with hydrogen ions (H + 2 ). Compared to protons, ions deliver a more conformal dose with a significant reduction in range straggling and beam broadening. Carbon ions are currently used and there are no current facilities providing helium therapy. We are investigating the feasibility of an FFAG approach for helium therapy, which has never been previously considered. We investigate emittance and demonstrate that the machine meets isochronicity requirements for fixed frequency RF.
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Papers by Rebecca Seviour