1,721,046 research outputs found
On the role of dissociative recombination on the effectiveness of a plasma neutralizer in DEMO fusion plant
No full textIn order to reduce the recirculating electrical power of DEMO the wall-plug efficiency of the additional heating systems plays a crucial role. The efficiency of the heating neutral beams (HNBs) of ITER is mostly limited by the gas neutralizer, whose efficiency is theoretically limited to about 55%. The use of a plasma neutralizer is a valuable alternative to increase the neutralization efficiency to about 80%, with a consequent improvement of the overall efficiency. The effectiveness of a plasma neutralizer increases with the ionization degree of the plasma, which is thus the key parameter of the system. The concept of a so-called “beam driven” plasma neutralizer (BDPN), in which the power to sustain the plasma is provided by the ion beam itself, is very appealing, and is explored in several works. Up to now though, a proof of principle for a plasma neutralizer was demonstrated only in experiments with an external plasma source and the scaling to an ITER-relevant plasma neutralizer suggests that a power in the order of 0.5 MW should be injected from outside to sustain a plasma with a 30% ionization degree. This work tries to bridge the gap between the models predicting the feasibility of a high efficiency BDPN and the experimental scaling. In particular, the role of the volume losses is highlighted and a much better agreement with experiment based scaling is obtained
AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DEBRIS FLOW ALONG STROBEL AND SOUTH PEZORÌES CHANNELS AT FIAMES (DOLOMITES, ITALY)
No full textThe area of Fiames is located on a narrow and flat valley, 2 km north to Cortina d’Ampezzo, and is bounded on the right side by the
Pomagagnon and Pezorìes peaks. At the transition between rock vertical cliffs and talus, about twenty debris channels originate and affect the
talus till the bottom of the valley. The Strobel and South Pezorìes channels were recently routed by debris flows in 2004 and 2006. Field surveys,
topographical and geo-morphological measurements were carried out to recognize the sediments volume that the debris flow can entrain during
triggering and routing phases. The estimate of the erodible sediment volume was obtained through the measurements of the geo-morphological
and sediments features of source areas including their locations (channel bank or bottom). The resultant estimate can help in the design of the
input debris flow hydrographs for dynamic modelling of debris flow and retain basins
Towards self-consistent modelling of negative ion beam acceleration
No full textNeutral beams are a valuable option to provide heat and current drive to a magnetically confined plasma. In addition they can be used as a diagnostics for the positive ion temperature and, in case of nuclear fusion reactions, for the amount of helium ash. In the case of ITER, stringent requirements are set on the acceptable beam divergence and aiming in order to propagate such beams up to the tokamak itself. Besides the well-known dependence of the beamlet optics on the beam energy and perveance, other important features affecting the optics are the ion spatial and velocity distribution at the plasma boundary facing the extractor, the so-called plasma meniscus. In a caesiated negative ion source, this distribution is influenced both by the birth energy of the negative ions and by the ion transport in the plasma itself. In this work we use a test particle code to investigate the negative ion transport up to the plasma meniscus and we use a standard ray-tracing code to trace the test particles that reached the meniscus inside the electrostatic accelerator. The coupling of the two codes is iterated up to numerical convergence. By this procedure, the angular distribution of the accelerated particles is found to be much more similar to the experimental ones than the one obtained by simple ray-tracing simulations
SPIDER Beam Homogeneity Characterization Through Visible Cameras
No full textHigh energy beams of negative hydrogen and deuterium ions are needed to heat and sustain the plasma of future nuclear fusion reactors, in particular, in the experimental reactor International Thermonuclear Experimental Reactor (ITER). Besides the beam energy, low divergence ( in deuterium and 350 in hydrogen. Source for the production of ions of deuterium extracted from a radio-frequency plasma (SPIDER), the full-size prototype of the ITER negative ion source, is equipped with a tomographic system consisting of 15 visible cameras, which observe the light produced by the interactions of the beam particles with the background gas after the accelerator, all around the beam itself, allowing a complete characterization of the beam shape and intensity. In fact, when the beam particles propagate in the background gas, they emit light in the visible range, due to the production of excited neutrals and ionization of the background particles. This light allows studying the beam properties since it is proportional to the beam current density itself. In the SPIDER ion source, magnetic and electric fields are used to optimize the beam current density, by reducing the electron temperature and density close to the extraction region. Also, cesium is evaporated in the plasma as a catalyst of negative ion production. In this work, the impact of these fields and of the cesium presence on beam properties will be discussed by means of visible tomography, using both the 1-D beam profiles and the 2-D tomographic reconstructions
TRONCO-CONICAL CUFFS CAN PROVIDE MORE ACCURATE BLOOD PRESSURE MEASUREMENTS THAN CYLINDRICAL CUFFS IN PEOPLE WITH LARGE ARMS
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Influence of plasma grid-masking on the results of early SPIDER operation
No full textSPIDER is the prototype negative ion source of the heating neutral beam injectors for ITER. As required by the ITER injector design, the SPIDER beam source is entirely contained inside the vacuum vessel, so that voltage holding depends on the background gas pressure. During the recent operation, the number of extraction apertures was limited in order to routinely operate the ion source with its nominal filling pressure while minimizing the vessel pressure. To close the apertures, a machined molybdenum sheet was installed downstream the plasma-facing electrode of the accelerator. In this contribution, we discuss the implications of this configuration, highlighting possible influences on the experimental results obtained so far, and the differences that can be expected in the future high-current operation (with all 1280 apertures). Among other topics, the possible effects on the use of caesium, the negative-ion density at the extraction region, the per-veance of the extractor and the profile of neutrals along the accelerator will be discussed
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
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