1,720,959 research outputs found
POWER EXHAUST DATA ANALYSIS AND MODELING OF ADVANCED DIVERTOR CONFIGURATIONS
Get PDFThe possibility to exploit fusion energy in a reliable, safe and available way is one of the greatest challenges in the worldwide research. Very hot magnetically confined plasma are required to achieve high rates of fusion reactions. However, these conditions are not compatible with the material facing the plasma. In order to protect the wall, a hot core confined region is created while most of the power and particles are ultimately exhausted in a properly design component of the reactor, the so-called divertor.
The Ph.D. activity presented in this thesis is carried out in the framework of EUROfusion program for the realization of a Demonstration power plant (DEMO) by the years 2050 . One of the most critical aspects has been recognized in the exhaust of huge amount of power which can severely damage the plasma facing component (PFC). Therefore, the analysis of the plasma conditions in the divertor region is essential to asses the reliability and the feasibility of a fusion reactor machine. In order to mitigate the power exhaust issue the fusion community is currently investigating several possible solutions as the use of alternative magnetic divertor configurations (AC) or the use of liquid metal as PFC. This thesis focuses on the study of the Scrape off Layer (SOL), the region where the particles coming out of the core are diverted towards the target plates. The modelling is performed by means of 2D edge codes on future and existing fusion reactors.
The first point in the analysis is the assessment of the edge plasma conditions in DEMO by considering a set of simplifying assumptions and taking into account a possible set of reference parameters. A scoping study is performed to evaluate the behaviour of the SOL plasma by varying the density and the transport coefficients. The numerical simulations are performed by means of the EDGE2D-EIRENE code. The results of the calculations predict divertor conditions totally unacceptable from an operational point of view. Most importantly, since the most used and validated code available in the fusion community are not able to deal with ACs, we perform a benchmark between EDGE2D-EIRENE and TECXY. The latter is a simple and fast code able to treat ACs. Despite the differences in the physical model adopted by the two numerical tools, the results shows a good match, especially in terms of power loads on the target plates and general trends of global quantities. On the other hand, discrepancies are observed in the electron density and temperature profiles on the outer divertor primarily due to the different numerical models adopted for the neutral particles description.
As a second step, we perform the analysis of an AC by comparing a conventional Single Null (SN) and a Quasi snowflake (QSF, characterized by a transition from Snowflake to X-Divertor configurations) magnetic configurations of DTT (Divertor Test Tokamak). The modelling is performed by means of EDE2D-EIRENE. The scoping study obtained by varying the upstream density investigates three different aspects: the effect on the attainment of the detachment, the effect on the power loads and the effect on the neutral particles behaviour. The simulations show that the QSF configuration is more prone to reach detached divertor conditions than the SN configurations. Furthermore, while in SN unacceptable power loads are foreseen onto the outer target plates, in case of QSF manageable values of the power peaks are obtained. This difference is primarily due to geometrical factors, especially the main driver is recognized in the flaring of the flux surfaces in the divertor region. By analysing the neutral particles behaviour, we see that a better confinement is achieved in QSF than in SN since the ionization front is not able to move towards the X-point. A preliminary analysis of liquid lithium divertor is also discussed. Since we simulate regimes dominated by the sputtering, minor differences are observed by comparing the liquid lithium divertor and the standard Tungsten one.
The last point of the research activity concerns the use of a different 2D edge code, i.e. SOLEDGE2D-EIRENE. Thanks to the high flexibility, this code is able to treat ACs. We discuss the preliminary results of a validation phase carried out by comparing the numerical results with the experimental one. While the upstream profiles are fairly reproduced by varying the diffusion coefficients, the target quantities shows mismatches in terms of electron density and temperature whereas the power profile is partially recovered. The results are then compared in terms of radiation distribution. The code is able to reproduce the 2D distribution in the high field side, even though discrepancies on the inner divertor baffle are observed. Finally, we show that improvements can be obtained by suitably defining the recycling coefficient
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
Detection of magnetic barriers in a chaotic domain: First application of finite time Lyapunov exponent method to a magnetic confinement configuration
No full textMagnetic field lines embedded in a plasma confinement system are often characterized by
a chaotic motion. This weakens the confinement properties of any magnetic configuration.
However, even in case of chaotic domains, magnetic barriers can emerge and limit the field
line motion itself. In the context of the numerical simulation of a Reversed-Field Pinch
configuration a new magnetic topology analysis, borrowed from previous fluid dynamic
studies, is discussed. This methodology relies on the behavior of the Finite Time Lyapunov
Exponent (FTLE) associated with the magnetic field. By referring to a previous work in which
the magnetic field is given in terms of analytical function the FTLE field shows the presence of ridges, special gradient lines normal to the
direction of minimum curvature, forming magnetic barriers. These ridges can be recognized
as Lagrangian Coherent Structures (LCSs) for the system, actually opposing the penetration
of magnetic field lines across them. In this article a more general numerical scheme for the
detection of the LCSs has been adopted that allows analysis of realistic cases in which the
magnetic fields are numerically known on a discrete mesh. After a validation test performed
on the analytical case, a first application to a numerical magnetohydrodynamics simulation
of the RFP, characterized by a broad chaotic region, has been performed. A strong magnetic
barrier has been observed that effectively limits the field lines motion inside the chaotic sea
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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