1,720,969 research outputs found
Numerical and experimental characterization of beams of negative ions and investigation on strategies for beam efficiency improvements
Full text linkThe research activity done during the three years Joint Doctorate in Fusion Science and Engineering was focused on negative ion sources and dedicated to numerical investigations of beam optics, experimental measurements and development of improvements for experimental devices. In particular, I carried out investigations on plasma source behavior and beam extraction under different operational conditions, paying special attention to beam optics improvement and co-extracted electron suppression efficiency, as well as analysing and developing solutions by means of numerical codes such as SLACCAD and OPERA, supported by dedicated post-processing by MATLAB scripts.
I investigated the beam properties for three negative ion beam sources: SPIDER and NIO1 at Consorzio RFX (Padova, Italy) and NITS at National Institute for Quantum and Radiological Science and Technology (QST, Naka, Japan). SPIDER is the full-scale prototype of the negative ion source for ITER negative ion beam injectors (NBIs) and is in the advanced construction and assembly phase, so no further design improvements could have been done. SPIDER is provided with several peculiar design solutions: I have numerically assessed the efficiency of such solutions related to beam optics with 40 beamlets (half SPIDER beamlet group). I participated in the joint experiments of Consorzio RFX and QST in the NITS facility. The aim of this collaboration was to prove experimentally, for the first time, the effectiveness of a specific magnetic field configuration adopted for ITER NBIs requiring the use of the so-called ADCM magnets to correct the residual magnetic deflection of the beamlets induced by the (CESM) magnets devoted to deflect the co-extracted electrons. In particular my contribution was to design the new extraction grid and the new magnets (both CESM and ADCM) to be installed on the source. I also cooperated to the data analysis. Lastly, for the NIO1 source, I participated in the experimental sessions since the beginning, and I gave my contribution to the spectroscopic characterization of the source and to beam optics characterization. These experimental observations suggested some upgrades needed for optics improvement. Hence, I moved in this direction designing a new extraction grid and new magnet configurations. Furthermore, the successful experimental evidences at NITS have made us confident to introduce ADCM also in NIO1. This design work was performed in strict collaboration with Laboratori Nazionali di Legnaro (LNL, Legnaro, Italy). Unfortunately, these upgrades will be not installed on the source before spring 2017 and thus no experimental evidences of beam optics improvements are available yet.
Concerning the thesis manuscript, it is constituted by five chapters, followed by an additional summary. Here is a brief summary of the chapter contents.
In the first chapter I give an introduction on Fusion and ITER, highlighting the need for the use of NBIs in future fusion devices and the general issues related to MITICA, which is the full size prototype of ITER NBI.
In the second chapter there is a general description of the theoretical considerations related to the physics of plasma in the source, beam extraction and optics, and main components constituting the ion sources. The final part of the chapter is dedicated to the presentation of the numerical tools available at Consorzio RFX: SLACCAD, EAMCC, COMSOL and OPERA. Concerning the latter, since it is the most important numerical tool I used during my PhD, I dwell more on the possibilities it can offer and I provide also a sensitivity study in order to increase the calculation precision.
While the first two chapters have essentially introductory purposes, the last three present the actual activities I performed on the three ion sources, SPIDER, NITS and NIO1, as briefly described so far. In particular each of the three chapters is focused on the activity done on just one machine.
Lastly, two appendixes supplement this thesis concerning further activities, which are loosely related to the rest. These are the development of an Excel GUI, in Visual Basic language, to simplify the interaction with NIO1 database (Appendix A) and investigations on the energy recovery system efficiency that NIO1 will feature in the future, an activity carried out in collaboration with CNR institute of Bari (Appendix B)
Multi-beamlet investigation of the deflection compensation methods of SPIDER beamlets
No full textSPIDER (Source for Production of Ions of Deuterium Extracted from a Rf plasma) is an ion source test bed designed to extract and accelerate a negative ion current up to 40 A and 100 kV whose first beam is expected by the end of 2016. Two main effects perturb beamlet optics during the acceleration stage: space charge repulsion and the deflection induced by the permanent magnets (called co-extracted electron suppression magnets) embedded in the EG. The purpose of this work is to evaluate and compare benefits, collateral effects, and limitations of electrical and magnetic compensation methods for beamlet deflection. The study of these methods has been carried out by means of numerical modeling tools: multi-beamlet simulations have been performed for the first tim
Design of the new extraction grid for the NIO1 negative ion source
Full text linkNIO1 is a compact source of negative ions jointly developed by RFX and INFN, to study the physics of production and acceleration of H- beams. Negative ions, up to 120 mA of current, are extracted from a radiofrequency driven plasma, by means of a gridded electrode (plasma grid, PG) featuring 9 apertures arranged in a 3x3 square lattice. The same aperture pattern is replicated in the following electrodes, allowing ion acceleration up to 60 keV. All electrodes are realized in copper, by electro-deposition technique, leaving empty slots in the metal to place magnets and to flow water for the grid cooling. The first set of electrodes was completed, installed in the source and tested. At the same time, an upgrade of the extraction system was carried out, in order to optimize the beam optics and to explore alternative electrostatic configurations. In particular, the accelerator will be modified by completely replacing the EG grid, exploiting the modularity of NIO1. The new electrode will feature other slots in between apertures, to place additional magnets. This allows testing different magnetic configurations, to optimize electron filtering and residual ion deflection. The present paper describes the theoretical activities driving the design of these new extractors, carried out with most updated numerical codes, and exploiting the synergy with the refined modeling of the 40 A ITER negative ion sources, under development at Consorzio RFX. Beam simulations are performed both with tracing codes (SLACCAD and OPERA) and with particle in cell codes (ACCPIC
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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