1,720,994 research outputs found
Design of electric and magnetic components of a negative ion accelerator in view of application to ITER Neutral Beam Injectors
Full text linkThe work of this PhD thesis has been developed inside the framework of magnetic confinement thermonuclear fusion and is connected in particular to the major worldwide experiment in this context, the future tokamak ITER. A very important component of ITER and of tokamaks in general is the Neutral Beam Injector (NBI), a device whose purpose is the production of an energetic beam of neutral particles capable to sustain the fusion reactions inside the reactor vessel. The prototype of the NBI for ITER, called MITICA, has been designed and will be constructed at Consorzio RFX, Padua, and its main requirement is the achievement of a Deuterium beam with 1 MeV of energy, 17 MW of power and 3600 s of duration.
This thesis is focused on the design of one of the crucial components of MITICA, the electrostatic accelerator, in which the electric and magnetic fields play a decisive role in determining the final performances. The work developed is chronologically collocated during the final three years of MITICA accelerator design, which is now finished.
The design activities carried out on electric and magnetic components of MITICA accelerator will be here presented together with the results of the experimental activities on prototypes and other existing accelerators.
A chapter will be dedicated to the results of code improvement activities.
This work can be read as the closure of MITICA accelerator design, in which all the remaining design issues have been faced and solved, and the operating scenario has been finalized
An efficient method for magnetic field and force calculation in complex permanent magnet and current arrangements
No full textA magnetic calculation code has been developed for modelling a multi-beamlet, multi-stage negative ion accelerator. This code has been recently improved with a precise and fast calculation of magnetic force between permanent magnets and current-carrying conductors, and self- and mutual- inductances involving rectangular or circular coils. The paper describes the formulation and the validation of force and inductance calculation through comparison with other codes and analytical solutions
Mapping of Magnetic Field of SPIDER by a Three-Axis Automatic Positioning System
No full textSPIDER is the prototype of the ion source of the neutral beam injector (NBI) for ITER, and is currently in operation at the Neutral Beam Test Facility (NBTF), Consorzio RFX, Padova, Italy. The magnetic field is important in SPIDER and, in general, in negative ion sources. It is required for filtering the fast electrons in the plasma source (magnetic filter field), thus for enhancing the negative ion production rate, and for suppressing the coextracted electrons in the accelerator (electron suppression field). In order to measure and map the magnetic field in SPIDER, a positioning system has been designed and realized, then applied with success during 2018. A three-axis system holds a Hall probe, and can be controlled manually or remotely by a graphical user interface. Once the three-axis system is installed on SPIDER, it can be programed to automatically move through the 1280 accelerator apertures and acquire magnetic field profiles. The development of this programable system allowed saving a considerable amount of time. This article describes the design and the realization of the magnetic field mapping system, along with the results of the measuring campaigns carried out in 2018 and the comparison with numerical models
Design of a System for Performing High-Voltage Holding Test Campaigns on a Mockup of MITICA Negative Ion Source
No full textMegavolt ITER Injector and Concept Advance- ment (MITICA) is the full-size prototype of the neutral beam injector (NBI) for the ITER currently under construction at the neutral beam test facility (NBTF) (Consorzio RFX, Padova, Italy). One of the main issues of such a complex machine is to secure a stable voltage holding of the ion source—accelerator complex—which is biased at −1 MV and constitutes a very large (cathodic) area, with respect to the ground (the vessel). Coordinated with the experimental program of the HV test facilities in Japan (QST, Naka) and in Italy (high voltage Padova test facility, Consorzio RFX), a test campaign is foreseen for 2020–2021, using the real MITICA vacuum vessel and a mockup of the ion source. This mockup can constitute a simple geometry, where the MITICA ion source is represented by a sphere (cathode), connected to the high-voltage bushing. A planar electrode (anode) will cover the lower part of the beam source vessel (BSV) and will be positioned at an adjustable distance from the sphere, to assure fine control of the electrostatic configuration. The experiments will be devoted to characterize the breakdown voltage as a function of the gap length and vacuum pressure. In this article, the design activity of the electrodes to be used during the campaign is presented
NBImag: A Useful Tool in the Design of Magnetic Systems for the ITER Neutral Beam Injectors
No full textNBImag is a code suitable for the design and opti- mization of complex magnetic field configurations, such as that of a multiaperture, multistage negative ion source and accelerator. The NBImag code has been developed for the design of the ITER neutral beam injector, whose full-size prototype, MITICA, is presently under construction in Padua, Italy. The ITER injector shall produce a focused beam of neutral particles (H or D) having an energy of about 1 MeV and a total power of 16.5 MW for 3600-s continuous operation. The NBImag code is based on an integral formulation and allows an efficient calculation of any static magnetic field configuration on the basis of the geometry of the magnetic sources, with linear material and permanent magnets. NBImag also includes magnetic force and inductance calculations, based on the same formulation. Thanks to the capability of efficiently describing a large number of permanent magnets with limited computational effort, NBImag has also been integrated with different automatic optimization procedures for the solution of inverse magnetic problems. This paper describes the formulation of the code and optimization algorithms, the vali- dation against analytical models and experimental measurements, and the application to the design of MITICA
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
Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator
No full textA new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative- ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the “concentration” of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be “intrinsically” cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved
Feasibility study of a flux-gate magnetic field sensor suitable for ITER neutral beam injectors
No full textITER Neutral Beam Injectors (NBIs) need to be shielded from the relatively strong stray magnetic field generated by the Poloidal Field Coils of the Tokamak. For this reason both the Heating Neutral Beams (HNB) and the Diagnostic Neutral Beam (DNB) will be provided with a Passive Magnetic Shield and with a system of Active Correction and Compensation Coils (ACCC). The ACCC will operate in feedback control and thus require the measurement of magnetic field inside the NBI vessel, i.e. in an environment subjected to the neutron flux coming from the Tokamak. To this purpose, magnetic sensors which are robust, radiation hard, drift-immune and remote-handling compatible are required.
Flux-gate magnetic sensors are a good candidate for this task, but commercial sensors of this kind have typically a limited measured range (below 0.1 mT).
The feasibility of a flux-gate sensor for the ITER NBI has been studied by developing a numerical model which includes magnetic core hysteresis, and which demonstrated that, by suitable choice of the core magnetic properties and geometry, it is possible to increase the measurement range by at least 2 orders of magnitude. On this basis, a flux-gate sensor prototype has been realized at Consorzio RFX. Experimental tests carried out so far have demonstrated that the measurement range can be increased to ∼10 mT with acceptable accuracy and frequency bandwidth
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
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