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Study of the power supply system for the acceleration grids of the iter neutral bean injector
Get PDFThermonuclear fusion is a promising alternative to hydrocarbons as a clean and almost unlimited source of energy, presently the only one having the potential to substitute completely the non-renewable resources. The increase and the volatility of the oil prices, the foreseeable forthcoming shortage of oil and natural gas and the apparent co-responsibility of the combustion of coal and hydrocarbons in the recent climate changes make fusion more and more interesting. ITER (International Thermonuclear Experimental Reactor) is a large-scale prototype of a fusion power plant, under construction in Cadarache, south of France. ITER, resulting from a large international cooperation, will be the most ambitious of a series of fusion experiments built and operated around the world, in which a gas of light nuclei is heated up to become plasma, and suspended into a toroidal vacuum chamber by means of powerful magnetic fields produced by electromagnets. If the plasma temperature is sufficient and if the magnetic confinement is good, the fusion reactions become probable enough to produce higher fusion energy than the energy necessary to sustain the fusion boundary conditions. The main aim of ITER is to prove the physical and technological feasibility of fusion as an effective source of energy and to develop the technologies to be implemented in the future fusion reactors.
In ITER, to heat the plasma, the contribution of 2 or 3 Neutral Beam Injectors (NBI) is necessary. In these devices, a beam of negative ions (40 A) is accelerated up to 1MeV by a set of grids having increasing potentials. Then, the beam is neutralized and injected into the ITER vacuum vessel, heating the plasma by collision with plasma particles. The NBI accelerator is fed by a dedicated power supply system (AGPS, Acceleration Grid Power Supply), rated for a total power of 54.7 MW. Being the technical requirements of the overall ITER NBI system well above the performances presently achieved in similar neutral beam injectors in fusion experiments, a test facility is foreseen and presently under construction in the CNR Research Area in Padova. In this facility, called PRIMA (Padova Research on ITER Megavolt Accelerator), the present NBI design will be tested and, where necessary, improvements and further developments of the NBI components will be implemented before their installation in ITER.
This thesis presents the studies carried out by the author on the AGPS system, in collaboration with the research group of Consorzio RFX and the researchers of the other institutions involved in the project. The objectives of these studies are the following: to verify the feasibility of the AGPS, to support the definition of a reference design and to verify the achievement of the required performance. In section 1, a brief introduction to the energy problem and the thermonuclear fusion is given. Section 2 describes the principle of a tokamak, the most promising configuration for a fusion reactor. Section 3 contains a short description of the ITER experiment. In section 4, the main components of the ITER NBI are presented, together with a brief introduction to the PRIMA test facility. In section 5, the power supply system of the ITER NBI and the layouts foreseen on ITER and PRIMA sites are introduced. The main requirements for the AGPS are given in section 6, focusing in particular on those related with the analyses presented in this thesis. In section 7, the reference design of the AGPS is revised and the calculations for the most important components of the AGPS conversion system are given. The reference design presented here, of course, is the result of the contributions of many researchers working under the respective national domestic agencies involved in the project. Moreover, some open points of the AGPS design are still under discussion and the AGPS specifications are not finalized yet, thus the parameters and the technical choices shown here not necessarily represent the final version that will be implemented in the real system. The same considerations are applicable to section 8, where the design of the AGPS control system is described. The performance of the AGPS system defined in the previous sections has been tested by using proper computer models and simulations, under normal and abnormal conditions. In sections 9, 10, 11 and 12, the models developed by the author and the results of the simulations are described. In section 13, some specific issues regarding the tests to be performed on the real AGPS system are investigated. In particular, an alternative type of dummy load is proposed by the author, and a solution to test the voltage control loop is studied, by means of original computer models and simulations. The conclusions of this work are summarized in section 14.La fusione termonucleare controllata costituisce una promettente alternativa agli idrocarburi quale fonte pulita e quasi illimitata di energia, attualmente la sola potenzialmente in grado di sostituire del tutto le fonti non rinnovabili. L’incremento e la volatilità dei prezzi del petrolio, la prevedibile futura scarsità di idrocarburi e l’apparente corresponsabilità della combustione di tali sostanze nei recenti cambiamenti climatici rendono la fusione sempre più attraente. ITER (International Thermonuclear Experimental Reactor) è un prototipo su larga scala di un reattore a fusione, in costruzione a Cadarache, nel sud della Francia. ITER, frutto di una vasta collaborazione internazionale, sarà il più ambizioso di una serie di esperimenti di fusione costruiti e resi operativi nel mondo, nei quali un gas di atomi leggeri è riscaldato fino a divenire un plasma e sospeso in una camera da vuoto toroidale per mezzo di potenti campi magnetici prodotti da elettromagneti. Se la temperatura del plasma è sufficiente e il confinamento magnetico è abbastanza buono, le reazioni di fusione diventano abbastanza probabili da produrre più energia di quanta non ne serva per sostenere le condizioni di fusione. Lo scopo principale di ITER è di provare la fattibilità fisica e tecnologica della fusione quale fonte di energia e di sviluppare le tecnologie che dovranno essere implementate nei futuri reattori a fusione.
In ITER, per riscaldare il plasma è necessario il contributo di 2 o 3 iniettori di atomi neutri (NBI). In questi dispositivi, un fascio di ioni negativi (40 A) è accelerato fino a 1 MeV da una serie di griglie aventi potenziali crescenti. Il fascio viene quindi neutralizzato e iniettato nella camera da vuoto di ITER, dove collide con le particelle di plasma contribuendo al loro riscaldamento. L’acceleratore dell’NBI è alimentato da un sistema dedicato (AGPS, Acceleration Grid Power Supply) dimensionato per 54.7 MW totali. Essendo i requisiti tecnici del sistema NBI nel suo complesso molto superiori alle prestazioni attualmente raggiunte in NBI simili operanti negli esperimenti di fusione, una test facility è prevista e attualmente in costruzione nell’area della ricerca del CNR di Padova. In questa facility, detta PRIMA (Padova Research on ITER Megavolt Accelerator), il progetto attuale dell’NBI verrà testato e migliorato laddove necessario e verranno implementati ulteriori sviluppi dei componenti dell’NBI prima della loro installazione in ITER.
Questa tesi espone gli studi condotti dall’autore sull’AGPS, in collaborazione con il gruppo di ricerca del Consorzio RFX di Padova e i ricercatori degli altri enti coinvolti nel progetto. Questi studi hanno lo scopo di verificare la fattibilità dell’AGPS, di supportare la definizione del progetto di riferimento e di verificare il raggiungimento delle prestazioni richieste. Nella sezione 1, è riportata una breve introduzione sul problema energetico e sulla fusione termonucleare controllata. La sezione 2 descrive il principio di funzionamento di un tokamak, la più promettente configurazione per un reattore a fusione. La sezione 3 contiene una breve descrizione dell’esperimento ITER. Nella sezione 4 vengono presentati i componenti principali dell’iniettore di ITER, oltre ad una breve introduzione sulla test facility PRIMA. In sezione 5, vengono introdotti il sistema di alimentazione dell’NBI e i relativi layout. I principali requisiti dell’AGPS sono forniti nella sezione 6, con particolare riguardo a quelli relativi alle analisi presentate in questa tesi. Nella sezione 7, si fornisce una revisione del progetto di riferimento dell’AGPS, descrivendo i calcoli dei principali componenti del sistema di conversione. Il progetto di riferimento presentato in questa tesi, ovviamente, è il risultato del contributo di molti ricercatori che operano all’interno dei relativi enti di ricerca nazionali coinvolti nella sua definizione. Inoltre, alcuni punti aperti del progetto dell’AGPS sono ancora in discussione, e le specifiche dell’AGPS non sono ancora state ultimate. Di conseguenza, i parametri e le scelte tecniche mostrati in questa tesi non rispecchiano necessariamente la versione finale che sarà implementata nel sistema reale. Le stesse considerazioni valgono per la sezione 8, in cui si descrive il progetto del sistema di controllo dell’AGPS. Le prestazioni dell’AGPS descritto nelle sezioni precedenti sono state verificate per mezzo di appositi modelli e simulazioni al calcolatore, sia in condizioni normali che anormali. Nelle sezioni 9, 10, 11 e 12 vengono descritti i modelli sviluppati dall’autore e i risultati delle simulazioni. Nella sezione 13, vengono studiate alcune questioni specifiche riguardanti i test da realizzarsi sull’AGPS reale. In particolare, l’autore propone un tipo di carico fittizio alternativo e studia un sistema per testare il controllo di tensione in catena chiusa, per mezzo di modelli al calcolatore e simulazioni originali. Le conclusioni della tesi sono riassunte nella sezione 14
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Studies on high voltage dc cable connection to supply the acceleration grids of the Neutral Beam Injector for DTT
No full textThe Divertor Tokamak Test facility (DTT) is the new tokamak under construction in Frascati (Italy), with the main aim of testing different divertor magnetic configurations and technologies in view of DEMO. The Heating and Current Drive function will be provided also by one Neutral Beam Injector (NBI), accelerating negative Deuterium ions with an energy of 510 keV, giving an output power of 10 MW maximum. The Acceleration Grid Power Supply (AGPS), with 3 stages rated 167 kV each, will feed the NBI accelerator. For optical reasons, the insulating gap among the acceleration grids is at the limit of the voltage holding in vacuum, therefore frequent arc breakdowns (BD) among the grids will occur, requiring the quick switch-off of the AGPS to limit the arc energy. For the AGPS, beside the ITER-like scheme including gas-insulated HV components, an innovative approach based on the Modular Multilevel Converter (MMC) technology is being considered. This would include air-insulated HV converters, requiring a huge building volume, which at present is not available in close proximity to the tokamak building. The alternative of installing the MMC converters in a new building to be erected in an available area located far from the tokamak, and connecting the AGPS to the load with HV coaxial cables, is under study. This paper presents the studies carried out to verify the impact of the cables length on the arc energy, in case of breakdown among the grids, and to estimate the magnitude of the voltage oscillations due to resonance effects. These oscillations can occur not only between each hot pole and the return conductor, endangering the cable insulation, but also between the return conductor and local ground, with potential consequences on the laying method, the human safety and the electromagnetic compatibility with sensitive apparatus nearby, which have all been evaluated
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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