1,721,002 research outputs found
Effect of magnetic field on voltage holding in the MITICA electrostatic accelerator
No full textMITICA is the complete full-scale prototype of a 17 MW Heating Neutral Beam Injector for ITER. This experimental device, presently under construction in Padova, includes a negative Ion Source (H- or D-), and an electrostatic Accelerator (1 MV, 40 A, 3600 s).
Voltage holding is recognized to be one of the most critical issues for the 1 MV accelerator operations, not only due to the complex multi-stage electrostatic accelerator structure, but also for the presence of magnetic field, which is necessary for deflecting the co-extracted and secondary electrons as early as possible, before they are accelerated. The required magnetic field is produced by a combination of several sources, such as permanent magnets and current-carrying conductors.
In order to avoid breakdowns, the design of the accelerator shall guarantee that electrostatic configuration and the pressure distribution correspond to an operating point located on the left branch of the Paschen curve, i.e. where the H2 gas pressure multiplied by the largest electrode distance (p.d) is always below a certain limit, which is 0.1-0.3 Pa.m. Actually, the presence of the magnetic field might reduce this limit, moving the left branch of the Paschen curve towards the operating point thus affecting voltage holding even during the conditioning phase.
In order to support the design of MITICA at low gas pressure and in the presence of magnetic field, an experimental campaign has been carried out at the High Voltage Padova Test Facility
Simulation, Code Benchmarking and Optimization of the Magnetic Field Configuration in a Negative Ion Accelerator
No full textSPIDER is a full-size Negative Ion Source and a multi-beamlet 100 kV accelerator, presently under con-
struction in Padova and is part of PRIMA, the test bed for the full development of the Heating Neutral
Beam system for ITER. During the final design, the SPIDER extractor and accelerator system has been
improved with respect to the original configuration. In particular, the magnetic configuration has been
optimized in order to improve the performances in terms of ion beam optics and aiming, and to obtain
an efficient filter for the extracted electrons
Voltage holding optimization of the MITICA electrostatic accelerator
No full textTwo Heating Neutral Beam Injectors (H-NBI) are planned to be installed in ITER with a total delivered heating power of 33 MW [1]. The main parameters are: 870 kV acceleration voltage with 46 A beam current for hydrogen beam, and 1 MV voltage with 40 A current for deuterium beam.
The voltage holding in the 1 MV ITER Neutral Beam Accelerator is recognized to be one of the most critical issues for long pulse (3600 s) beam operation, due to the complex electrostatic structure formed by electrodes polarized at different potentials immersed in vacuum or low-pressure gas. As a matter of fact, the system shall work in a p × d range at the left of the Paschen curve where the classical Townsend breakdown criterion is no longer valid. The voltage holding is governed by the mechanism of the long gap insulation in high vacuum, not yet well consolidated from the physical point of view.
This paper is aimed to describe the optimization of the voltage holding capability for MITICA electrostatic accelerator. The results of this analysis will constitute the input for the probabilistic model [3] which is adopted to predict the breakdown probability by means of 2D analyses of the multi electrode – multi voltage system
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
HVPTF -The high voltage laboratory fo ITER Neutral Beam test facility
No full textIn the MITICA research program for the construction of the ITER Neutral Beam Injector prototype, a Laboratory for the investigation on high voltage holding in vacuum has been set up. This Laboratory - HVPTF: High Voltage Padova Test Facility - is presently capable of experiments up to 300 kV dc, and planned for the upgrade to 800 kV. The specific mission for this ancillary lab is the support to the electrostatic design and construction of the MITICA accelerator and the development and testing of HV components to be installed inside the MITICA accelerator during its operation.
The paper describes the structure of the lab, characterized by a high degree of automation and reports the results of the commissioning at 300 kV and the first results of voltage holding between test electrodes
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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