1,720,979 research outputs found
Thermal and transport characterization of rfp plasmas from electron temperature data
No full textThe work deals with electron tempearature and transport analysis in RFP plasams; in particular the following topics are discussed:
- the commissioning of the edge Thomson Scattering in RFX-mod for temperature evaluation;
- the commissioning of the laser blow-off system in RFX-mod for impurity transport characterization
-the analysis of RFP helical states in term of electron temperature, diffusivity and confinement on the experiments RFX-mod (Padua) and MST (madison, WI).Il presente lavoro sviluppa una caratterizzazione dei plasmi RFP dal punto di vista termico e di trasporto; in particolare vengonodiscussi i seguenti punti:
-lo sviluppo della diagnostica di Thomson Scattering di bordo per la misura della temperaturea elettronica;
-lo sviluppo del sistema di laser blow off per l'iniezione di impurezze e lo studio del loro trasporto
-l'analisi degli stati elicoidali negli RFP, in termini di caratteristiche termiche e di confinamento, negli esperimenti RFX-mod(Padova) e MST(Madison-WI
Dual-angle, self-calibrating Thomson scattering measurements in RFX-MOD
No full textIn the multipoint Thomson scattering (TS) system of the RFX-MOD experiment the signals from a few spatial positions can be observed simultaneously under two different scattering angles. In addition the detection system uses optical multiplexing by signal delays in fiber optic cables of different length so that the two sets of TS signals can be observed by the same polychromator. Owing to the dependence of the TS spectrum on the scattering angle, it was then possible to implement self-calibrating TS measurements in which the electron temperature Te, the electron density ne and the relative calibration coefficients of spectral channels sensitivity Ci were simultaneously determined by a suitable analysis of the two sets of TS data collected at the two angles. The analysis has shown that, in spite of the small difference in the spectra obtained at the two angles, reliable values of the relative calibration coefficients can be determined by the analysis of good S/N dual‐angle spectra recorded in a few tens of plasma shots. This analysis suggests that in RFX-MOD the calibration of the entire set of TS polychromators by means of the similar, dual-laser (Nd:YAG/Nd:YLF) TS technique, should be feasible
Dual-laser, self-calibrating Thomson scattering measurements in RFX-mod
No full textA self-calibrating Thomson scattering technique, based on using two lasers of different wavelength and never implemented before in a fusion experiment, is tested for the first time in RFX-mod. The method employs two laser systems, Nd:YAG (λ = 1064 nm) and Nd:YLF (λ = 1053 nm), fired in sync through the same plasma volume. The combination of the two scattered spectra, individually recorded, is used to simultaneously obtain the measurements of the electron temperature Te and the relative calibration coefficients of the polychromator spectral channels sensitivities Ci. This work is a continuation of the dual-angle technique, a similar alternative method. Due to the small difference in the wavelengths of the two lasers, the sensitivity of this method is low in RFX-mod and reliable measurements of the calibration coefficients could not be obtained on a shot-to-shot basis, but only with a statistical analysis of a reasonable number of pairs of laser shots with good signal-to-noise ratio. The dual-laser method can be applied to most fusion devices and could provide continuous online monitoring of the spectral transmission of the detection system. This may prove essential in larger devices (ITER), where access for traditional calibration is difficult
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
A feasibility study of a NBI photoneutralizer based on nonlinear gating laser recirculation
No full textThe neutralization efficiency of negative ion neutral beam injectors is a major issue for future fusion reactors. Photon neutralization might be a valid alternative to present gas neutralizers, but still with several challenges for a valid implementation. Some concepts have been presented so far but none has been validated yet. A novel photoneutralization concept is discussed here, based on an annular cavity and a duplicated frequency laser beam (recirculation injection by nonlinear gating). The choice of lithium triborate as the material for the second harmonic extractor is discussed and a possible cooling method via crystal slicing is presented; laser intensity enhancement within the cavity is evaluated in order to quantify the achievable neutralization rate. Mockups of the critical components are proposed as intermediate steps toward system realization
Impurities removal by laser blow-off from in-vacuum optical surfaces on RFX-mod experiment
No full textAn in situ window cleaning system by laser blow-off through optical fiber has been developed on the basis of a feasibility study previously presented. The beam generated by a Q-switched Nd:YAG laser is launched in a vacuum box into a high damage threshold optical fiber through a lens. The fiber output is focused on the impurities-coated surface of a vacuum window exposed to the plasma of the RFX-mod experiment, and it is remotely controlled with an xy motion system to scan the entire surface. We first investigate the energy density threshold necessary to ablate the deposited impurity substrate on removed dirty windows: above threshold, a single laser pulse recovers ∼95% of the window transmission before its exposure to the plasma, while below it the efficiency of the cleaning process is too poor. The system so conceived was then used to clean the three collection windows of the Main Thomson scattering diagnostic on RFX-mod. We also present results obtained applying the same technique to the SiO-protected Al mirror used for the Zeff diagnostic: an energy threshold for efficient impurity removal without mirror damage is first identified, then ablation tests are executed and analyzed in terms of recovered reflectivity. The SIMS technique is used both with windows and mirror to study the composition of surfaces before and after the ablation
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
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