Materials Design - Towards a Functionally Graded Electrical Conductor

In this study, we discuss functionally graded (FG) materials as pulsed electrical conductors. These conductors can be designed to be more efficient and longer lasting by applying numerical modeling tools. One focus is on limiting the thermal fatigue damage in conductors caused by very high temperatures that develop during pulse heating. We have quantified the effect of various grading functions on the pulsed Joule heating generated and the peak temperature experienced in the conductors of an electromagnetic launcher by using a 1D numerical code and a state of the art 3D coupled finite element code, EMAP3D. Because FG materials incorporate applications-tailored compositions, structures, and dimensions, smoothly graded properties in lateral and longitudinal cross sections are obtainable. The Solid Freeform Fabrication (SFF) processing approach allows for architectures with a series of important features. These features include the selective use of high efficiency conducting materials in the core, preconditioned conductor/structure interfaces, and built-in features for enhanced cooling where necessary.Mechanical Engineerin

Bėgių tipo atvirojo kanalo elektromagnetinės svaidyklės magnetomechaninio efekto tyrimas

The dissertation investigates the electromagnetic launcher electromagnetic properties and their influence on mechanical construction. The main object of research is open bore two rail construction electromagnetic launcher. The dissertation aims to investigate the distribution of electromagnetic forces and their influence over the electromagnetic launcher construction volume. The work presents five tasks such as the electromagnetic and mechanical model application of the numerical model. The first task is formulated to rewiev the literature. The next two tasks are formulated to calculate the distribution of electromagnetic forces throughout the electromagnetic launcher construction volume. The last two tasks investigate the effect of the forces distribution differences over the electromagnetic launcher construction. The dissertation work consists of an introduction, four chapters, general conclusion, references, a list of publications by the author on the topic of the dissertation, a summary in Lithuanian and five annexes. The introductory chapter discusses the research problem, relevance of the work, introduces the object of the research, formulates the aim and the tasks of the work, describes the research methodology, scientific novelty of the work, considers the practical significance of the work results and defensive statements. At the end of the introduction, the publications and reports published by the author of the dissertation and the structure of the dissertation are presented. Chapter 1 is devoted to review the electromagnetic launcher analyses methods in literature. A brief overview of the adaptation and development history of electromagnetic launchers are provided. At the end of the chapter, conclusions are formulated, and the tasks of the dissertation are refined. Chapter 2 presents the structure and parameters of the electromagnetic launcher. According to this type of launcher, the electromagnetic and mechanical models were developed. The mathematical model of each modeling and boundary conditions are described, and the conclusions are presented. Chapter 3 and 4 provide the results of electromagnetic and mechanical modeling. The dependence between electromagnetic and mechanical problems are described. Conclusions are presented at the end of both sections. 4 articles have been published on the topic of the dissertation in the scientific journals included in the Clarivate Analytics Web of Science list, one article is in conference materials in the Clarivate Analytics Web of Science Proceedings database, and two is in peer-reviewed international conferencing materials. 4 presentations on the subject of the dissertation have been given in conferences at national and international levels

Investigation of flat capacitor discharge electromagnetic launchers

In this thesis, studies of flat or pancake type electromagnetic launcher systems are described. The studies involved the development of several numerical models, and are supported throughout by experimental investigation. The models were based on a coaxial filamentary division technique, and the results they provided were compared with those from a commercial electromagnetic finite element modelling package. They were used to investigate some of the many possible launcher structures and power supply arrangements, as part of a wide-ranging parametric study. The aim of this thesis was to gain an insight into the factors that affect the performance of the launchers. Several different techniques were implemented to reduce the computation time. Practical experimentation provided a clear demonstration of the launcher technology, and supplied valuable model validation data. To aid the experimental work new projectile speed and yaw measurement systems were developed, and these were supported by results from a high-speed camera. A novel dual projectile launcher was tested, and was shown to improve the launch efficiency and to operate at higher energies, due to the reduction in drive coil recoil. Projectile deformation was investigated in both solid discs and flat annular projectiles

Numerical and Analytical Methods in Electromagnetics

Like all branches of physics and engineering, electromagnetics relies on mathematical methods for modeling, simulation, and design procedures in all of its aspects (radiation, propagation, scattering, imaging, etc.). Originally, rigorous analytical techniques were the only machinery available to produce any useful results. In the 1960s and 1970s, emphasis was placed on asymptotic techniques, which produced approximations of the fields for very high frequencies when closed-form solutions were not feasible. Later, when computers demonstrated explosive progress, numerical techniques were utilized to develop approximate results of controllable accuracy for arbitrary geometries. In this Special Issue, the most recent advances in the aforementioned approaches are presented to illustrate the state-of-the-art mathematical techniques in electromagnetics

Numerical 3D simulation of a full system air core compulsator-electromagnetic rail launcher

Multiphysics problems represent an open issue in numerical modeling. Electromagnetic launchers represent typical examples that require a strongly coupled magnetoquasistatic and mechanical approach. This is mainly due to the high velocities which make comparable the electrical and the mechanical response times. The analysis of interacting devices (e.g., a rail launcher and its feeding generator) adds further complexity, since in this context the substitution of one device with an electric circuit does not guarantee the accuracy of the analysis. A simultaneous full 3D electromechanical analysis of the interacting devices is often required. In this paper a numerical 3D analysis of a full launch system, composed by an air-core compulsator which feeds an electromagnetic rail launcher, is presented. The analysis has been performed by using a dedicated, in-house developed research code, named "EN4EM" (Equivalent Network for Electromagnetic Modeling). This code is able to take into account all the relevant electromechanical quantities and phenomena (i.e., eddy currents, velocity skin effect, sliding contacts) in both the devices. A weakly coupled analysis, based on the use of a zero-dimensional model of the launcher (i.e., a single loop electrical equivalent circuit), has been also performed. Its results, compared with those by the simultaneous 3D analysis of interacting devices, show an over-estimate of about 10-15% of the muzzle speed of the armature

Parameter study of ICRH wave propagation in IShTAR

A crude first assessment of how waves behave is commonly made relying on decoupled dispersion equation roots. In the low density, low temperature region behind the last closed flux surface in a tokamak where the density decays exponentially and where the lower hybrid resonance is crossed but where the thermal velocity is small enough to justify dropping kinetic (hot plasma) effects the study of the wave behaviour requires the roots of the full cold plasma dispersion equation. The IShTAR (Ion cyclotron Sheath Test ARrangement) device will be adopted in the coming years to shed light on the dynamics of wave plasma interactions close to radio frequency (RF) launchers and in particular on the impact of the waves on the density and their role in the formation of RF sheaths close to metallic objects. As IShTAR is incapable of mimicking the actual conditions reigning close to launchers in tokamaks; a parameter range needs to be identified for the test stand to permit highlighting of the relevant wave physics. Studying the coupled dispersion equation roots allowed us to find a suitable operation domain for performing experiments

Power requirements for electron cyclotron current drive and ion cyclotron resonance heating for sawtooth control in ITER

13MW of electron cyclotron current drive (ECCD) power deposited inside the q = 1 surface is likely to reduce the sawtooth period in ITER baseline scenario below the level empirically predicted to trigger neo-classical tearing modes (NTMs). However, since the ECCD control scheme is solely predicated upon changing the local magnetic shear, it is prudent to plan to use a complementary scheme which directly decreases the potential energy of the kink mode in order to reduce the sawtooth period. In the event that the natural sawtooth period is longer than expected, due to enhanced alpha particle stabilisation for instance, this ancillary sawtooth control can be provided from > 10MW of ion cyclotron resonance heating (ICRH) power with a resonance just inside the q = 1 surface. Both ECCD and ICRH control schemes would benefit greatly from active feedback of the deposition with respect to the rational surface. If the q = 1 surface can be maintained closer to the magnetic axis, the efficacy of ECCD and ICRH schemes significantly increases, the negative effect on the fusion gain is reduced, and off-axis negative-ion neutral beam injection (NNBI) can also be considered for sawtooth control. Consequently, schemes to reduce the q = 1 radius are highly desirable, such as early heating to delay the current penetration and, of course, active sawtooth destabilisation to mediate small frequent sawteeth and retain a small q = 1 radius.Comment: 29 pages, 16 figure

Experimental validation of multipactor effect for ferrite materials used in L- and S-band nonreciprocal microwave components

This paper reports on the experimental measurement of power threshold levels for the multipactor effect between samples of ferrite material typically used in the practical implementation of L- and S-band circulators and isolators. For this purposes, a new family of wideband, nonreciprocal rectangular waveguide structures loaded with ferrites has been designed with a full-wave electromagnetic simulation tool. The design also includes the required magnetostatic field biasing circuits. The multipactor breakdown power levels have also been predicted with an accurate electron tracking code using measured values for the secondary electron yield (SEY) coefficient. The measured results agree well with simulations, thereby fully validating the experimental campaign.This work was supported by European Space Agency (ESA) through research project "Novel Investigation in Multipactor Effect in Ferrite and other Dielectrics used in High Power RF Space Hardware" (ref. AO 1-7551/13/NL/GLC), and by MINECO (Spanish Government) under R&D projects TEC2016-75934-C4-1-R, TEC2016-75934-C4-2-R and the ERDF co-funded project TEC2014-55463-C3-3-P