1,721,303 research outputs found
Non-invasive beam profile monitor for medical accelerators
No full textA beam profile monitor based on a supersonic gas-curtain is currently under development for transverse profile diagnostics of electron and proton beams in the High Luminosity LHC. This monitor uses a thin supersonic gas curtain that crosses the primary beam to be characterized under an angle of 45 degrees. The fluorescence caused by the interaction between the beam and gas-curtain is detected using a specially designed imaging system to determine the 2D transverse profile of the primary beam. Another prototype monitor based on beam induced ionization is installed at The Cockcroft Institute. This paper presents the design features of both the monitors, the gas-jet curtain formation and various experimental tests, including profile measurements of an electron beam, using helium, nitrogen and neon as gases. Such a non-invasive online beam profile monitor would be highly desirable also for medical LINAC's and storage rings as it can characterize the beam without stopping machine operation. The paper discusses opportunities for simplifying the monitor design for integration into a medical accelerator and expected monitor performance
Studies towards an enhanced understanding of electron beams and their diagnostics
No full textA large part of current research and innovation capacity depends on high quality electron beams. Electron accelerators are found in many applications from cancer therapy, cargo scanners, high energy particle colliders, synchrotron light sources to free electron lasers. Electron beams also offer exciting opportunities for developments at the cutting edge of science, for example on novel accelerating schemes which promise accelerating gradients several orders of magnitude higher than what can be realised with conventional radiofrequency accelerators.
Whilst R&D into the optimisation of electron accelerators has been performed over many decades, further improvements are still required so their potential can be fully exploited. This includes studies into advanced instrumentation to yield more precise information about the beam itself, novel simulation tools that model the physics of emission and interaction processes, as well as improved beam generation and shaping schemes to enhance the achievable beam brightness.
In the frame of this PhD work, different areas of electron beams and associated technologies have been studied whilst still pertaining to the same question: How can we better understand the generation, control and use of electron beams? The thesis is split into three main sections: After a general introduction to the subject, studies into electron emission and initial beam shaping are covered in chapter 2, before the results from investigations into novel beam loss detection techniques are presented in chapter 3.
In any accelerator based light source, maintaining the beam quality is crucial. The electron source itself is a key element that determines the achievable beam quality. A variety of source materials are currently under test across many institutes to better understand emission characteristics and to identify the best materials and optimum preparation methods. Here, one experimental set-up at the Cockcroft Institute has been considered. The Transverse Energy Spread Spectrometer (TESS) apparatus uses electrostatic elements to measure both the transverse and longitudinal energy properties of electron beams generated from photocathodes. This then provides detailed information about the electron emission process and allows optimisation of beam generation schemes. To enhance the understanding of the experimental data, a dedicated particle tracking code has been developed which uses accurate maps obtained from simulation or experiment to represent all electromagnetic fields of the set-up. This code has then been used to study two different techniques to measure the longitudinal energy spread of electrons emitted from gallium arsenide. The first technique was to use a wire mesh as an energy filter which the electrons must pass through, the second was to generate a potential difference between the cathode source and detector system. Experimental results are presented for both techniques and the analysis is supplemented with simulations. Monte Carlo results are in good agreement with experimental data, however, through this analysis it is found that using the meshes as a wire filter may not be an efficient method of measuring the longitudinal energy distribution curve as a result of the potential distribution surrounding the wire meshes. The second method is sufficient to the task however the resolution of the technique may be affected by focusing effects around the meshes.
Measurement and detection of beam loss is important for any accelerator as unwanted losses yield reduced beam transmission and cause higher background noise. It is crucial in high energy accelerators where unwanted loss particles could easily damage parts of the accelerator and the experiments. Currently used techniques, however, are often limited in their dynamic range, spatial and time resolution, radiation hardness and can be expensive. A detector based on optical fibres with photodetector readout has been studied as part of this work as a detector for a future electron-positron collider. It can cover large distances at the expense of many smaller localised detectors. The ultimate performance of this detector is strongly affected by the light sensor at the fibre end. This in turn limits the performance to locate beam loss intensity and position and hence ultimately limits the understanding of beam loses along an accelerator. To this end Silicon Photomultipliers have been studied as an advanced light sensor that shows great promise for beam loss applications. Preliminary models are compared to experimental data and it is shown that the detector performance in this application is limited by the finite number of pixels available to fire along with pixel recovery/dead time. Measurements carried out at the CLIC Test Facility at CERN using an optical fibre systems are presented and used to assess the system’s performance to specific beam structures. Several techniques are used to analyses signals recorded by multiple detectors however it is found that the layout of optical fibres, which could not be changed, limited full understanding, however, these results are the basis of later experiments which fully measure the effect of a fibre optic beam loss monitor to different beam structures and additional changes to the set-up, which may aid further tests, are covered
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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