1,721,148 research outputs found
Novel radiometric imaging diagnostics for charged particle beams
Full text linkDiagnostics are crucial to the operation of all particle accelerator facilities. They provide a means of optimising beam parameters and monitoring beam quality for users. However, for the next generation of accelerators, operating in extreme parameter spaces, most current beam diagnostics will fail; either through material failure or lack of resolution. This thesis presents three new diagnostic concepts to address this imminent diagnostic need. These novel diagnostics are supported by a simulation-based algorithm, successfully benchmarked throughout this work. All work has been conducted by the Author unless otherwise stated and referenced. The first technique measures sub-micron transverse beam profiles using optical transition radiation (OTR). Simulations were used to design a new imaging system, which was then installed at KEK (Japan). OTR images were then collected for a range of beam sizes. Comparisons were then made with simulations to successfully achieve sub-micron beam size measurements. Validation of these results was found in the agreement across different imaging systems for fixed beam parameters, providing a self-consistency check for the algorithm in lieu of alternate corroboration. The next diagnostic is a bunch length monitor for ∼<100 fs particle bunches; based on imaging the spatial distribution of coherent transition radiation (CTR) in the THz regime. Simulations demonstrated a relationship between image width and intensity, with bunch length. A THz imaging system was then installed at MAX IV (Sweden). CTR images were taken for a range of compressions. Maximum compression was successfully identified by monitoring relative changes in the properties of the images. Bunch lengths were then acquired from these images through comparison with simulations.
Finally, the optical performance of a Digital Micro-mirror Device (DMD) was assessed. Image resolution produced by a DMD was quantified by measuring the Point Spread Function (PSF) of an imaging system, which was capable of remotely replacing a DMD with a planar mirror. The PSFs were measured using the sub-micron focus of a laser. Results show no measurable alteration to a PSF with the introduction of a DMD. This provides a foundation for the development of future diagnostics centred around this device.
This thesis provides several validated proof-of-principle experimental results and supporting simulations. Future work has been identified for each topic, only possible following the results presented here, which will provide an array of novel next generation diagnostics
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
Supersonic gas-jet based beam profile monitor
No full textIons and in particular antiprotons, stored and cooled at low energies in a storage ring or at rest in traps, are highly desirable for the investigation of a large number of basic questions on fundamental interactions, on the static structure of exotic antiprotonic atomic systems or of (radioactive) nuclei as well as on the time-dependent quantum dynamics of correlated systems.
Such low energy, low intensity beams pose, however, new challenges on beam instrumentation, as they require least intrusive diagnostics operating at ultra-high vacuum pressures of the order of 1
Longitudinal density monitor for the LHC
Full text linkThe longitudinal density monitor (LDM) is primarily intended for the measurement of the particle population in nominally empty rf buckets. These so-called satellite or ghost bunches can cause problems for machine protection as well as influencing the luminosity calibration of the LHC. The high dynamic range of the system allows measurement of ghost bunches with as little as 0.01% of the main bunch population at the same time as characterization of the main bunches. The LDM is a single-photon counting system using visible synchrotron light. The photon detector is a silicon avalanche photodiode operated in Geiger mode, which allows the longitudinal distribution of the LHC beams to be measured with a resolution of 90ps. Results from the LDM are presented, including a proposed method for constructing a 3-dimensional beam density map by scanning the LDM sensor in the transverse plane. In addition, we present a scheme to improve the sensitivity of the system by using an optical switching technique. © 2012 American Physical Society
Radiation impact of collimation beam losses in the LHC and HL-LHC
Full text linkBeam dynamics and Monte Carlo beam-matter interaction simulations play a vital role in the design and performance assessment of high-energy proton and ion colliders. The collimation system of the Large Hadron Collider (LHC) is leading by example with its proven ability to protect and assure an unobstructed operation during the past years. This thesis aims to further develop the complex simulation chain involved in the study of the collimation related beam losses as well as to accurately estimate its predictive capabilities. An unprecedented benchmark against Beam Loss Monitor (BLM) measurements is presented with extensive analysis of particle showers and their origins. Furthermore, the proton losses during the Run 2 operational period (2015-2018) in the betatron cleaning insertion region are estimated. Predictions for upcoming High Luminosity-LHC (HL-LHC) are made utilising a new scaling method based on the integrated proton intensity. The new scaling method and the proton loss estimates for Run 2 are benchmarked against passive dosimeter measurements during the same years. In addition, the tools are then applied in order to quantify the radiation impact that beam losses have in the collimation system itself as well as in the normal and Super-Conducting (SC) magnets. The short term radiation effects concerning the collimator material robustness and the power deposited in the SC coils are examined. Lastly, the long-term degradation of organic (dose) and crystalline materials (DPA), found in the magnets and collimator absorber blocks, respectively, are presented for the HL-LHC lifetime
FEL R&D within LA3NET
No full textThe detailed diagnostics of the shortest beam pulses in free-electron lasers still pose significant challenges to beam instrumentation. Electro-optical methods are a promising approach for the non-intercepting measurement of electron bunches with a time resolution of better than 50 fs, but suitable optical materials need to be better understood and carefully studied. In addition, adequate timing systems with stability in the femtosecond regime based on mode-locked fibre laser optical clocks, and actively length-stabilised optical fibre distribution require further investigation. These important problems are being addressed within the broader EU-funded LA³NET project by an international consortium of research centres, universities, and industry partners. This contribution gives an overview of the wider LA³NET project and results from initial studies in both areas. It also describes the events that LA³NET will organize
Characterization studies of carbon nanotubes as cold electron field emitters for electron cooling applications in the Extra Low ENergy Antiproton (ELENA) ring at CERN
Full text linkElectron emission allows the extraction of electrons from a material, commonly a metal or a semiconductor. There are three main processes for achieving electron emission: thermionic emission, photo-emission, and field emission.
Electron emission is of high importance in electron cooling. Electron cooling guarantees beam quality in low-energy antimatter facilities. In the Extra Low ENergy Antiproton ring (ELENA), the electron cooler reduces the emittance growth of the antiproton beam so that a focused and bright beam can be delivered to the experiments at the unprecedentedly low energy of 100 keV.
Cold emission can be beneficial in the electron cooler of ELENA for avoiding the use of a thermionic cathode. The thermionic cathode imposes constraints on the beam temperature, the fragility of the gun, and the gun design.
A cold cathode may solve all these problems at once. In this thesis work, cold emission is achieved via field emission from carbon nanotubes (CNTs).
For the electron cooler of ELENA, the lifetime and the current stability of the electron source play a primary role. Furthermore, it is important to pulse the cathode to promptly enable/disable the cooling process and to change the electron beam energy according to the cooling stage and the ELENA beam cycle.
This work proves that a CNT array can stably emit for hundreds of hours and a record emission time of 1500 hours has been proved. The operation of a CNT cathode in current switching mode has also been tested. Rise and fall times below 1 μs have been proved with unaltered current emission stability during operation.
Several constraints can arise when using CNTs as electron sources. Among these, the role of an extracting grid needs accurate evaluation. In this Ph.D. work simulations of the beam passage through micro-metric grids were performed. These simulations were aimed at studying the effect of the grid on the beam current, trajectory, and transverse energy. It was found that a grid with a squared pattern, 15 μm hole size and 3 μm bar width, does not significantly alter the beam trajectory and the beam transverse energy. The transparency of such a grid was about 68%.
Finally, guidelines for mitigating possible issues related to the design of a CNT-based cold cathode electron gun were addressed. A gun layout has been proposed after the optimization of all components through electromagnetic simulations.
The findings of the research carried out within the frame of this Ph.D. project are applicable to a wide range of CNT applications: from electron guns for accelerator science to X-ray tubes, CNT-based televisions, and any case where electron extraction is required.
The findings from studies into extracting grids and gun design have an even wider reach and benefit any application where particle extraction and transport are involved
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