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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
Get PDFThe 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
Beam Steering and Radiation in Ultrashort Silicon and Germanium Bent Crystals at the MAinzer MIkrotron
No full textVariations on the Author
Get PDF“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
Bent Crystal Design and Characterization for High-Energy Physics Experiments
Get PDFBent crystal are widely used as optics for X-rays, but via the phenomenon of planar channeling they may act as waveguide for relativistic charged particles beam as well, outperforming some of the traditional technologies currently employed. A physical description of the phenomenon and the resulting potential for applications in a particle accelerator is reported. The elastic properties of the anisotropic crystal lattice medium are discussed, introducing different types of curvature which can enable a wide array of bending schemes optimized for each different case features. The technological development of machining strategy and bending solutions useful for the fabrication of crystals suitable in high energy particle manipulations are described. As well as the high precision characterization processes developed in order to satisfy the strict requirements for installation in an accelerator. Finally, the characterization of channeling phenomenon in bent crystal is described, pointing out several experimental setups suitable to comply each specific case constrains
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Get PDFWe 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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