1,721,221 research outputs found
SOLPS-ITER modeling of divertor scenarios for EU-DEMO
Full text linkWe developed a first single null divertor scenario for EU-DEMO with the SOLPS-ITER code, including all charge states of D, He and Ar in the simulation and kinetic analysis of the neutral gas, but still leaving out drifts. Our results suggest that a partially detached divertor condition can indeed be obtained, with a corresponding peak heat flux on targets to ≈2 MW m-2, within the expected tolerable steady-state limits. The plasma re-attaches ≈30 cm (measured along the plate) from the low field side strike point deep in the SOL, with a consequent raise in the electron temperature up to ≈16 eV outside the detached region, which requires further analysis to assess a possible role of sputtering, especially considering W self-sputtering. The plasma we developed exhibits Z eff ≈ 1.9 in the core, and a pumping speed a few hundred's m3 s-1 to maintain steady-state; this points to the need of further studies to better characterize the He accumulation in the core region
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
Parametric Studies of the EU DEMO Central Solenoid
No full textThe Central Solenoid (CS) is at the core of the EU DEMO tokamak, and has a strong impact on the tokamak design and the overall machine size. By ramping its current, the CS generates a change of magnetic flux, which initiates the plasma, and induces and controls the plasma current. In the context of the conceptual design studies for DEMO coordinated by EUROfusion, the Swiss Plasma Center has developed a simple pre-dimensioning methodology, assuming uniform current density in the solenoid winding pack, and considering the use of Nb3Sn and REBCO. The effects of grading of the superconductor and structural steel are also discussed. Since the CS for the EU DEMO will experience tens of thousands of charge/discharge cycles during its lifetime, mechanical fatigue considerations are taken into account. The proposed methodology has been used for the preliminary design of the CS winding pack, and for a number of parametric analyses in the context of the integrated physics and engineering studies for the EU DEMO machine (identifying the relationship between key performance parameters of the solenoid, such as the generated magnetic flux and the fatigue lifetime)
Figure of merit for divertor protection in the preliminary design of the EU-DEMO reactor
No full textThis paper discusses the criteria to be used in the preliminary design phases of the EU-DEMO reactor to ensure the performance of the divertor without compromising the stability of core plasma or the fusion power generation. This work refers to a lower single null conventional divertor using actively cooled solid metal plasma-facing components and with extrinsic seeding for heat flux dissipation, which is the solution currently being adopted for EU-DEMO. The analysis does not consider the role of edge localised modes, and also neglects major off-normal events like disruptions. It is shown that it is necessary to fulfil two high-level requirements, namely: (i) the concentration of seeded impurities has to be lower than some critical value in order to not compromise the fusion plasma performance or stability and (ii) damage to the divertor plate in the case of accidental plasma reattachment must be avoided for a sufficiently long time in order to ensure safe, controlled termination of the plasma discharge. These requirements are needed because in a device like EU-DEMO, other strategies relying on mass injection are considered more likely to cause a loss of plasma stability at full current, with dramatic consequences for the integrity of plasma facing components. Two figures of merit, corresponding to these criteria, have been identified in the existing literature and discussed. The dependence of such figures of merit on the relevant machine parameters (major radius and toroidal magnetic field) is analysed. Initially, the analysis is carried out using a simple 0D physics approach and subsequently by means of the systems code PROCESS, which allows for consideration of further parameters, such as aspect ratio and elongation. The main conclusion of the present work is that the simultaneous fulfilment of both requirements limits the viable EU-DEMO size both in terms of major radius R and in terms of toroidal magnetic field BT. Finally, an attempt to extend the EU-DEMO related conclusions to a more general level is made
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
Burn control strategies using plasma elongation in DEMO
No full textIn this paper, a feedback control algorithm to reduce the DEMO fusion power fluctuations due to the presence of possible disturbances and unpredicted events is proposed. Fluctuations can be limited controlling temperature and densities of the different plasma species by means of a set of actuators like electron cyclotron resonance heating, fuelling rate modulation and/or impurity injection. However, electron cyclotron resonance heating is expensive in terms of power cost and impurities are difficult to control because it is hard to remove them from the core. A possible alternative is to use plasma shape as a virtual actuator and in particular elongation through plasma shape magnetic control. This work exploits the possibility to use elongation modifications in a coordinated way with electron cyclotron resonance heating power, and electron density, for real time control. The integrated control scheme implements a supervised control allocation strategy and accounts for constraints coming from actuator limits as maximum elongation, maximum ECRH power or maximum electron density, but also on other key plasma parameters like plasma safety factor and Greenwald density limit. Numerical results of the overall control scheme to compensate the effect of uncontrolled argon injection and tungsten flake event are obtained within the DEMO flight simulator based on Fenix
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