1,721,043 research outputs found
Studies and measurements on cavity beam position monitors for novel electron linacs
Full text linkBeam Position Monitors (BPM) are the most frequent non-intercepting diagnostics used at nearly all Linacs, cyclotrons and synchrotrons. Their main purpose is to measure the position of the center of mass of the beam. There are many types of BPMs, which have different design, developed by taking into accounts the beam characteristics and the level of accuracy and resolution wanted. One of the most recent types, which is now used world-wide, is the Cavity Beam Position Monitor (cBPM). The latter became popular mainly because they can achieve the highest measurement resolution of all types of BPMs (up to tens of nanometers) even for low charge beams. Moreover, they can also be used to give information on the beam charge. The trade-off is that the mechanical design is complex and that high frequency read-out electronics is typically needed, which could increase the overall cost of the system.
This dissertation is focused mainly on Cavity Beam Position Monitors and their application on novel electron LINACS. The research performed is particularly focused on the resolution of such devices and it also takes into consideration the read-out electronics, that for many aspects is the most critical part of the system. The techniques used to measure the resolution are explained, as well as all the experiments performed both in laboratory and in presence of beams
Design realization and commissioning of RF Power system and accelerating structures for a Gamma Source
Full text linkThanks to the recent technological progress in the fields of high power lasers and high brightness linac accelerators, new Gamma and X ray sources based on electron-photon interaction are under development in several laboratory world-wide. These kind of sources uses Inverse Compton scattering in the collision between a relativistic high quality electron beam and high power optical laser pulses to generate secondary photon beams of unique performances. These photon beams are suitable for a wide range of applications and open new perspectives in many research fields. In particular gamma rays in the energy interval between 1-20~MeV are of great interest for basic research and application studies in the fields of nuclear physics and photonics. In this framework, a very innovative Compton source is under construction in Magurele (RO), by the EuroGammaS association, with the aim to generate photon beams in that energy range, characterized by unprecedented performances in terms of mono-chromaticity, brilliance, spectral density, tunability and polarization. The realization of this source called ELI-NP-GBS is in the framework of the European Extreme Light infrastructure (ELI) project that pursues the creation of an international laser research infrastructure. The challenging parameters of this source rely on the performances of the Linac and in particular of his radiofrequency (RF) system. The electron accelerator is a high brightness normal conducting RF Linac consisting of two S-band (2856 MHz) and twelve C-band (5712 MHz) RF structures. The main advantages of using a Linac accelerator are the energy "tunability" and the excellent electron beam quality that is possible to obtain. The accelerator will be operated at a repetition rate of 100 Hz. For every RF pulse up to 32 electron bunches, each one carrying 250 pC of charge, separated by 16 ns, will be accelerated. The Linac is required to achieve a normalized emittance in both planes better than 0.5 mm mrad and energy spread below 0.1\%. To guarantee these performances in a reliable and stable way, innovative and advance RF components have been developed. The aim of this thesis is the study, design and commissioning of the main components of RF system used for the realization of a state of the art gamma source such as the ELI-NP-GBS. High power RF sources driven by solid state modulators have to feed the accelerating structures with high pulse to pulse amplitude stability and RF pulse uniformity in order to minimize the electron beam energy spread. An innovative C-band High Order Mode (HOM) damped RF cavity has been conceived and designed in order to avoid beam emittance and energy spread degradation due to the Beam Break-Up instability along the Linac. In addition the S-band RF Gun has been realized with an innovative technique called "Gasket-clamping technique'' and implements new radiofrequency features to sustain the 100 Hz repetition rate operation. All these devices have been realized and tested and the results obtained are reported in this work. Taking into account the extremely good results obtained by RF Gun realized with the gasket-clamping technique, in the last part of this dissertation, it has been explored the possibility to extend this fabrication procedure to the realization of an entire travelling wave Linac structure. This technique, thanks to the use of RF/vacuum special gaskets, allows avoiding the brazing process thus reducing the fabrication costs, the risk of failure and improving the performances of the device in terms of reachable peak electric field. To demonstrate the feasibility of the implementation of such technique an accurate electromagnetic and mechanical design of an S-band travelling wave structure has been performed
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
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
Implementation of the fast RF feedback on the DAΦNE beam longitudinal dynamics simulation code
No full textAs reported in other papers1,2, multibunch instabilities in DAΦNE have been studied by means of a dedicated simulation code describing the beam-cavity HOM interaction in the time domain. The radiation damping effect and the bunch-by-bunch feedback system aimed at curing the multibunch instabilities were also in
- …
