1,720,984 research outputs found
Neutronic Studies For A Compact High-Field Tokamak Neutron Source
No full textA critical aspect of the design of a tokamak-based neutron source is to ensure that radiation limits of the structural and magnet-insulating materials are not approached during the lifetime of the tokamak. To this end, we present an exploratory neutronics study of a materials testing facility that is based on Ignitor, a high-field tokamak. It shown that sufficient radiation damage to test materials located in the Ignitor first wall can be obtained by sustaining a reaction rate of 3.33×1019 neutrons per second for 7 operational months. Solutions to mitigate terminal damage to the toroidal field coil insulators, including its substitution for modern radiation-resistant insulators and the use of advanced radiation shield materials, are explored, and their implication for the design of the facility is discussed
Optimization of tritium breeding ratio in ARC reactor
Full text linkAffordable Robust Compact reactor is a conceptual design for a Tokamak conceived by Massachusetts Institute of Technology (MIT) researchers. The design of this tokamak is under development and update. One of the key parameters for fusion reactor power plants is the tritium breeding ratio (TBR), which has to guarantee the tritium self-sufficiency. The tritium inventory circulating in a fusion power plant must be minimized. In the meantime, to enhance plant's economics, the amount of tritium generated and stored should be maximized, since it would be used to startup new reactors. Both of the aforementioned trends meet their best in a TBR as high as possible. In this work, ARC tritium breeding ratio is studied and optimized. Taking advantage of Monte Carlo neutron transport codes, several configurations of ARC's blanket and vacuum vessel have been analyzed in order to find the most effective one for a high TBR. The study takes into account different materials for the structure, such as Inconel718, V-15Cr-5Ti and Eurofer97. Moreover, it scans different width of coolant's channels and evaluates the effect of lithium-6 enrichment in the blanket looking for the best configuration in terms of TBR
Compact Tokamak Neutron Sources As A First Step Towards Hybrid Fission-Fusion Reactors
No full textAn Ignitor-like tokamak that is compact, high field, and high density device, could make full use of the its intense neutron flux, without reaching ignition as a source of neutrons for materials testing in support of a fission-fusion hybrid device. The main features of this High Field Neutron Source Facility, which would have about 50% more plasma volume than Ignitor, are illustrated and the R&D required in order to achieve relevant dpa quantities in test materials are discussed. Several full-power months of operation are sufficient to obtain relevant radiation damage values in terms of dpa, and a scoping study of shielding the magnetic insulators to reduce radiation damage has been performe
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
ARC reactor: Radioactivity safety assessment and preliminary environmental impact study
Full text linkThe Affordable Robust Compact (ARC) reactor is a conceptual design for a Tokamak conceived by Massachusetts Institute of Technology researchers. The ARC design is under development and update. Since ARC will be a D–T tokamak, neutron generation and material activation will be main issues for safety studies and assessment of environmental impact and siting questions. The safety assessment goal for ARC is to demonstrate that it could be easily sited in the US, without public health and environmental problems and the need of any emergency plan implying population evacuation or sheltering. Another safety feature that will be verified is the need of a containment building in which the reactor should be surrounded. Starting from activation studies already developed for the ARC's vacuum vessel structure and the liquid blanket as well, a further and deeper analysis, that includes the first wall and neutron multiplier layer activation, has been carried out. Afterwards, taking advantage of the RESRAD population dose code, the study arrives to the assessment of doses to most exposed individuals from accidental activated material release in atmosphere, including possible tritium releases: radioactive safety limits for ARC environmental impact are finally defined
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