1,354,328 research outputs found
New schemes and experiments for high efficiency beam steering through coherent effects in bent crystals
No full textIl cristallo curvo può effettivamente deflettere il fascio delle particelle cariche mediante effetti coerenti nel campo elettrico del reticolo cristallino. Poiché il questo campo è più di un ordine di grandezza più forte del campo che può essere ottenuto nei moderni magneti superconduttori, un cristallo curvo può essere considerato un elemento degli acceleratori molto prospettico. Può essere applicato in particolare, per gli scopi di estrazione o collimazione a base del cristallo. Inoltre la
deflessione nel forte campo elettrico cristallino è molto promettente per la generazione di radiazione elettromagnetico intenso. Pertanto, lo sviluppo degli schemi nuovi per deflessione delle particelle cariche ad alta efficienza mediante gli effetti coerenti è dell'importanza fondamentale per la fisica degli acceleratori. In questo lavoro vengono proposti e sviluppati i schemi nuovi. I questi schemi sono studiati con gli simulazioni, usando il codice CRYSTAL specialmente sviluppato. Inoltre, alcuni schemi sono verificati sperimentalmente, non solo prevvedendo una visione della fisica delle interazioni coerente in un cristallo curvo, ma fornindo anche un feedback sull'affidabilità delle simulazioni. Il codice CRYSTAL è stato sviluppato per calcolare le traiettorie delle particelle cariche nel campo elettrico interplanare o interassiale, tenendo in conto dello scattering incoerente su i nuclei e gli elettroni. Il vantaggio del questo codice è la simulazione della soppressione dello scattering multiplo incoerente a causa della presenza di una struttura cristallina. Inoltre, il codice supporta la variazione dei parametri iniziali, consentendo di calcolare un set dei dati per un set delle valori dei parametri iniziali durante una sola esecuzione del codice. La parallelizzazione MPI consente di applicare il codice al supercomputer, sebbene molti casi possano essere calcolati in una macchina personale. Il questo codice è stato applicato per le simulazioni di tutti gli effetti coerenti, studiati in questo lavoro. Sono stati studiati, simulati e ottimizzati gli schemi diversi di deflessone dei protoni con l'energia del Future Circular Collider di 50 TeV, in particolare gli effetti del volume reflection, del multiple volume reflection in one bent crystal (MVROC) e nella sequenza dei cristalli curvi. Un
altro schema importante è stata la combinazione dell'effetto di channeling planare e MVROC usando channeling nei piani cristallini inclinati. Ciò consente di aumentare l'accettazione angolare di channeling e di applicare MVROC alle particelle non catturate nelle condizioni di channeling. Il cristallo curvo in questo caso funzionerà anche come il separatore del fascio. Inoltre channeling può essere amplificato con applicazione del taglio piano stretto, riducendo lo spazio delle fasi delle
particelle positive in channeling. È stato dimostrato che la combinazione del questo effetto con channeling in piani inclinati consente di raggiungere l'efficienza di deflessione fino al 99,9%. In questo lavoro, channeling e volume reflection degli elettroni di subGeV in un cristallo curvo vengono studiate sperimentalmente e con le simulazioni. Viene riportata un'efficienza di channeling record di 40% degli elettroni di 855 MeV in un cristallo curvo di silicio presso Mainzer Mikrotron MAMI. Ciò diventa possibile con l'applicazione di un cristallo curvo ultracorto da 15 μm, riducendo considerevolmente il contributo dello scattering incoerente rispetto a tutti i casi precedentemente considerati. Inoltre, viene riportata la prima evidenza di channeling delle particelle negative nel cristallo curvo del germanio all'energie di subGeV. In entrambi i casi sono state eseguite le misure della lunghezza dechanneling, dell'efficienza di channeling e degli angoli di volume reflection. I risultati sono in accordo con la teoria e le simulazioni. L'effetti nuovi, legati al processo di channeling planare, sono previsti, ovvero l'oscillazioni di channeling e quasichanneling planare nelle distribuzioni dell'angolo di deflessione. L'idea dei questi effetti consiste nella trasformazione dell'oscillazioni di una particella, essendo in condizioni
di channeling, o di una particella soprabarriera, che si muove ancora a un angolo piuttosto piccolo rispetto un piano di cristallo, in una serie dei picchi nella distribuzione angolare del fascio deflesso da un cristallo curvo. L'oscillazioni planari di channeling nella distribuzione angolare di deflessione si rappresentano da picchi equidistanti e possono essere rivelate solo per le particelle positive. L'oscillazioni di quasichanneling sono rappresentate da picchi non equidistanti e possono essere osservate per le particelle di entrambi i segni. Il modello teorico di entrambi i tipi di picchi è stato creato e verificato mediante gli simulazioni. Inoltre, la prima osservazione sperimentale dell'oscillazioni planari di quasichanneling è riportata per gli elettroni e per i positroni di 20.35 GeV. L'esperimento è stato condotto presso lo SLAC Facility for Advanced Accelerator Experimental Tests. Le posizioni dei picchi misurate erano in accordo con la teoria e le simulazioni fatti con il codice CRYSTAL. Entrambi i tipi dell'oscillazioni possono essere applicati per la misurazione e la regolazione dell'allineamento dei cristalli al fine di raggiungere l'efficienza di channeling più alta. In particolare, la procedura di fitting delle posizioni dei picchi delle oscillazioni di quasichanneling, eseguite in questo lavoro, consente di misurare l'allineamento del cristallo e la sua curvatura, usando solo una distribuzione dell'angolo di deflessione. Tutti i risultati del questo lavoro sono rilevanti per l'applicazione degli cristalli curvi in futuri progetti degli acceleratori e delle collidere per la collimazione del fascio e gli scopi di estrazione, nonché per la generazione di radiazione elettromagnetico intenso.Bent crystal can effectively deflect charged particle beam by means of coherent effects in the electric field of crystal lattice. Since this field is more than one order of magnitude stronger than the field that can be achieved in modern superconducting magnets, a bent crystal can be considered as a very perspective accelerator element. It can be applied in particular, for crystalbased extraction or collimation purposes. Moreover deflection in strong cristalline electric field is very promising for
generation of intense electromagnetic radiation. Therefore the development of the new schemes for high efficiency steering of charged particles by means of coherent effects is of crucial importance for accelerator physics. In this work the new schemes are proposed and developed. These schemes are studied through computer simulations by specially developed CRYSTAL simulation code. Moreover, some of them are verified experimentally, not only giving an insight into the physics of coherent interactions in a bent crystal, but also providing a feedback concerning simulations reliability. The CRYSTAL simulation code has been designed to calculate charged particles trajectories in interplanar or interaxial electric field taking into account incoherent scattering on both nuclei and electrons. The advantage of this code is simulations of suppression of incoherent multiple scattering due to the presence of crystal structure. Moreover, the code supports the varying the initial parameters, allowing one to calculate a set of data for a set of values of initial parameters during only one run of the code. MPI parallelization allows one to apply the code at supercomputers, though a lot of cases can be calculated at a personal mashine. This code was applied for simulations of all the coherent effects, studied in this work. Different schemes of steering of protons at the Future Circular Collider energy of 50 TeV were studied, simulated and optimized, in particular, the effects of volume reflection, multiple volume reflection in one bent crystal (MVROC) and in a sequence of bent crystals. Another importan scheme was the combination of the planar channeling effect and MVROC by means of channeling in skew crystal planes. This allows one both to increase the angular acceptance of channeling and to apply MVROC to the particles not captured under the channeling conditions. The bent crystal in this case will work also as a beam splitter. Moreover channeling itself can be amplified by the application of the narrow plane cut, reducing the phase space of positive channeling particles. It was shown, that the combination of this effect with channeling in skew planes allows one to achieve the deflection efficiency up to 99.9%. In this work channeling and volume reflection of subGeV electrons in a bent crystal is also studied both experimentally and by simulations. A record channeling efficiency of 40 % of 855 MeV electrons in a silicon bent crystal at Mainzer Mikrotron MAMI is reported. This becomes possible by the application of ultrashort bent crystal of 15 μm, considerably reducing the incoherent scattering contribution with respect to all the cases previously considered. Moreover, the first evidence of negatively charged particle channeling in germanium bent crystal at subGeV energies is reported. For both cases the measurements of dechanneling length, channeling efficiency and the volume reflection angles were carried out. The results are in agreement with theory and simulations. New effects, related to the planar channeling process, are predicted, namely planar channeling and quasichanneling oscillations in the deflection angle distributions. The idea of these effects consists in transformation of oscillations of a particle, being under channeling conditions, or of an overbarrier particle, moving still at rather small angle w.r.t. a crystal plane, into a series of peaks in the angular distribution of the beam deflected by a bent crystal. Planar channeling oscillations in the deflection angular distribution represent themselves by equidistant peaks and can be revealed only for positive particles. The quasichanneling oscillations are represented by nonequidistant peaks and can be observed for particles of either sign. The theoretical model of both kinds of peaks was created and verified by simulations. Moreover the first experimental observation of planar quasichanneling oscillations is reported for both 20.35 GeV electrons and positrons. The experiment was carried out at the SLAC Facility for Advanced Accelerator Experimental Tests. The measured peak positions were in agreement with both theory and simulations by the CRYSTAL code. Both kinds of oscillations can be applied for measurement and adjustment of the crystal alignment in order to reach higher channeling efficiency. In particular the fitting procedure of the peak positions of quasichanneling oscillations, carried out in this work, allows one to measure both crystal alignment and its curvature by using only one deflection angle distribution. All the results of this work are relevant for the application of bent crystals in future accelerator and collider projects for beam collimation and extraction purposes as well as for intense electromagnetic radiation generation
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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 method to align a bent crystal for channeling experiments by using quasichanneling oscillations
No full textA method to calculate both the bent crystal angle of alignment and radius of curvature by using only one distribution of deflection angles has been developed. The method is based on measuring of the angular position of recently predicted and observed quasichanneling oscillations in the deflection angle distribution and consequent fitting of both the radius and angular alignment by analytic formulae. In this paper this method is applied on the example of simulated angular distributions over a wide range of values of both radius and alignment for electrons. It is carried out through the example of (111) nonequidistant planes though this technique is general and could be applied to any kind of planes. In addition, the method application constraints are also discussed. It is shown by simulations that this method, being in fact a sort of beam diagnostics, allows one in a certain case to increase the crystal alignment accuracy as well as to control precisely the radius of curvature inside an accelerator tube without vacuum breaking. In addition, it speeds up the procedure of crystal alignment in channeling experiments, reducing beamtime consuming
Variations on the Author
No full text“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
No full textWe 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
Experimental evidence of independence of nuclear de-channeling length on the particle charge sign
No full textUnder coherent interactions, particles undergo correlated collisions with the crystal lattice and their motion result in confinement in the fields of atomic planes, i.e. particle channeling. Other than coherently interacting with the lattice, particles also suffer incoherent interactions with individual nuclei and may leave their bounded motion, i.e., they de-channel. The latter is the main limiting factor for applications of coherent interactions in crystal-assisted particle steering. We experimentally investigated the nature of de-channeling of 120 GeV/c e- and e+ in a bent silicon crystal at H4-SPS external line at CERN. We found that while channeling efficiency differs significantly for e- (2 ± 2 %) and e+ (54 ± 2 %), their nuclear de-channeling length is comparable, (0.6 ± 0.1) mm for e- and (0.7 ± 0.3) mm for e+. The experimental proof of the equality of the nuclear de-channeling length for positrons and electrons is interpreted in terms of similar dynamics undergone by the channeled particles in the field of nuclei irrespective of their charge
Planar channeling and quasichanneling oscillations in a bent crystal
No full textParticles passing through a crystal under planar channeling are captured by a continuous potential and experience transverse oscillations in their motion. As channeled particles approach the atomic planes, they are likely to be dechanneled. This effect is being used in ion-beam analysis with MeV energy. We study this effect in a bent crystal for positive and negative particles within a wide range of energies in sight of application of such crystals at accelerators. We look for the conditions for the observation or not of channeling oscillations in the deflection angle distribution in experiments where the beam passes through the bent crystal. Indeed a new kind of oscillations in the deflection angle distribution, strictly related to the motion of over-barrier particles, i.e. quasichanneled particles, is predicted. Such oscillations, named planar quasichanneling oscillations, possess a different nature than channeling oscillations. Through computer simulation, we study this effect and provided a theoretical interpretation for them. We show that channeling oscillations can be observed only for positive particles while quasichanneling oscillations can exist for particles with either sign. The conditions for experimental observation of channeling and quasichanneling oscillations at existing accelerators with available crystal are found and optimized
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Full simulations of beam dynamics of crystal-basedextraction from the DESY II Booster Synchrotronusing BDSim simulation code boosted withG4ChannelingFastSimModel
No full textIn order to perform full simulations of crystal-based extraction from an accelerator, a combination of simulationcodes for beam dynamics in an accelerator and channeling physics in crystals is required. Our solutionexploits the Beam Delivery Simulation (BDSIM) [1], an extensive library that contains thick lens acceleratortracking routines and a wide variety of accelerator components and magnets. BDSIM utilizes the Geant4toolkit [2] to simulate both the transport of particles in an accelerator and their interactions with acceleratormaterials. Additionally, BDSIM provides an easy way to implement new accelerator components through auser interface. We have utilized this interface to create a bent crystal as a new component and integratedGeant4 version 11.2.1, which includes the G4ChannelingFastSimModel [3], to incorporate channeling physicsinto this crystal.We have developed a complete BDSIM simulation model of the DESY II Booster Synchrotron to simulate thecrystal-based extraction process of 6 GeV electrons using BDSIM combined with G4ChannelingFastSimModel.We simulate the setup [4] that has already been published and compare the simulation results. We also discussthe feasibility of conducting the first proof-of-principle experiment.[1] L.J. Nevay et al., CPC 252 107200 (2020).[2] J. Allison et al., Nucl. Instrum. Meth. A 835, 186-225 (2016).[3] A. Sytov et al., JKPS 83, 132–139 (2023).[4] A. Sytov, G. Kube et al. Eur. Phys. J. C 82, 197 (2022)
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
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