1,721,012 research outputs found
Analysis of a flat, dielectric-loaded, ion cyclotron, test antenna by using three electromagnetic codes
No full textThe present work compares the results coming out from the following three Ion Cyclotron antenna tools: HFSS, COMSOL Multiphysics and the TOPICA code. A simplified flat antenna geometry, working at 30 MHz, is used as benchmark. The comparison is carried out with respect to the scattering matrix and the RF potentials, i.e., the line integrals of the electric field along the flux tubes of the equilibrium magnetic field. Various operational configurations characterized by different antenna load clearance are considered. Very good agreement can be observed among the codes for all the simulated configurations in terms of scattering parameters. RF potentials also match as
regards to patterns, trends as well as absolute values
Coupling and near-field simulations of ion-cyclotron antennas: Numerical validation of the perfectly matched layer technique for several density profiles
Full text linkA simplified, flat, plasma-loaded, ion-cyclotron antenna has been simulated using three different modeling approaches and a comparison of simulation outputs is presented in this paper. Several plasma profiles with different density gradients and distances between the antenna and the cutoff density have been used as benchmark for the numerical simulations, which have been run at 30 MHz by means of two tools. The one is the TOrino Polythecnic Ion-Cyclotron Antenna (TOPICA) code that has been repeatedly used and validated for this type of problems. The other tool is the finite-element method (FEM) of a commercial software, where inhomogeneous anisotropic materials can be defined and the perfectly matched layer technique can be adopted. In this tool, two models of antenna load have been implemented: an equivalent dielectric, locally matching the perpendicular propagation constant of the fast wave in the plasma, and a cold plasma model. The simulation results by such models are compared with the results by TOPICA, which relies on a 1-D inhomogeneous, hot plasma
Load-tolerant external matching unit based on a wideband hybrid coupler for the ICRH system of DTT
No full textIn the first phase of the Divertor Tokamak Test Facility (DTT), the goal of coupling a RF power of 3 MW to the plasma will be reached with a single ICRH module constituted by 4 generators, 2 or 4 External Matching Units (EMU) and 2 antennas. The operation with high levels of RF power into ELMy H-mode plasmas requires a robust and reliable Load-Tolerant EMU. Currently the most appropriate solution, ensuring a VSWR at the generators under the safety threshold of 1.5:1, will be based on a Wideband 2-section coaxial Hybrid Coupler operating in the frequency range of 60−90 MHz. HFSS and CST-MS simulation software was used for the optimization of the characteristic impedances and lengths of the transversal and longitudinal branches aimed to achieve excellent performance (amplitude and phase balance at the output ports, and low reflection at the input port) over the entire frequency range. The analysis has been carried out for Zo = 50 Ω and 30 Ω coaxial transmission lines in terms of S-parameters and electric field. Several good solutions with an amplitude imbalance about ±0.25 dB and a return loss lower than −20 dB in a large part of the frequency range will be presented. Then a simulation of the overall (end-to-end) EMU (Wideband Hybrid Coupler with shifter, stub and service stub in each of the 2 output branches) exploiting a suitable circuital solver of Ansys Electronics tool of HFSS, has been implemented. The resilience of the EMU has been tested determining the VSWR in input and the amplitude balance at the outputs for a typical resistive and reactive loading variation occurring during ELMs at f = 75 MHz and compared with the results at 65 MHz and 85 MHz
Radio-frequency undulators, cyclotron auto resonance maser and free electron lasers
Full text linkWe discuss a hybrid Free Electron Laser (FEL) architecture operating with a RF undulator provided by a powerful Cyclotron Auto-Resonance Maser (CARM). We outline the design elements to operate a compact X-ray device. We review the essential aspects of wave undulator FEL theory and of CARM devices
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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