1,721,040 research outputs found
Coupling and Hysteresis Loss Measurements on the ITER CS Module #4
No full textThe fourth CS Module (CSM#4) of the ITER Central Solenoid was tested in November/December 2022 at the premises of General Atomics, Poway, US. During the measurement campaign, the CSM#4 was submitted to dumps of the transport current from different initial values (from 0 to 40 kA) to 0 kA. The tests were performed both in virgin conditions and after 10 slow current cycles. This work analyses the experimental dumps of the CSM#4 to determine the losses in the CICC via the measurement of the energy deposited in the supercritical helium. The losses in the magnet are presented pointing out the impact of the slow current cycles. The latter also allow one measuring the hysteresis losses of the magnet. In the previous module tests, as well as in the tests of a single layer solenoid (referred to as CS Insert), it was very difficult to retrieve reliable values of the hysteresis losses in the CS conductor. However, the knowledge of hysteresis losses is crucial for a correct heat inventory of the magnet in operation. This study reports the results of their measurement, which represents a relevant added value of the CSM#4 tests. Finally, the experimental data are compared with the results of analytical models developed for the loss computation
Modeling of Quench in the ITER Poloidal Field Coils
Get PDFThe SuperMagnet suite of code is here applied to study the Poloidal Field (PF) and Correction Coils (CC) and their cryogenic distribution during a quench in the PF coils. In the model, more than 65 km of conductors, bus-bars, 3 km of pipes, the cold circulator, several bypass and control valves are implemented to reproduce the cryogenic circuits. The quench is simulated with an external heat disturbance at the location characterized by the lowest temperature margin during the plasma scenario. Two different approaches have been followed. In the first approach, the coils are initially assumed at their nominal conditions in 'cold' state (4.4 K), before the beginning of the operating cycle. In the second approach, the initial conditions of the quench simulation correspond to those obtained in the time instant at which the lowest temperature margin is found during the plasma scenario. The main parameters to be set for the intervention of the quench protection system (threshold voltage and validation time) are finally discussed
Transport and anisotropic properties of coated conductors deposited by PLD on steel substrates
No full textCoated conductors deposited by a novel high-rate pulsed laser deposition (PLD) technique on ion-beam-assisted-deposition (IBAD) layers of yttria-stabilized zirconia (YSZ) on non-magnetic steel ribbons were investigated. An XRD analysis of the superconducting layers showed in-plane alignments with a FWHM from 10 to 25 degrees and an out-of-plane alignment of better than 2 degrees. We report on the field and temperature dependence of the critical transport current density in these YBa2Cu3O7-delta films of various thickness, In addition, the angular dependence of the transport current at various external magnetic fields is presented. Thirdly, artificial pinning centers were introduced into the superconductors by neutron irradiation. The influence of these defects on the critical current densities and on the anisotropy ratio are discussed
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
Characterization of YBCO coated conductors deposited by LPE on MgO substrates
No full textResults on the field and temperature dependence of the: critical transport current density in YBa2Cu3O7-delta coated conductors of various thickness are presented. The conductors were deposited by liquid phase epitaxy on RE-123 buffer layers on MgO substrates. The analysis of the remanent fields in magnetization loops with different maximum external field provides information about the inter- and intragrain current distribution. From the reverse leg of the magnetization loops the average grain size in the YBCO layer can be estimated. The results of these magnetic measurements are compared to those obtained from magneto-optical imaging. Modifications of the defect structure by neutron irradiation are reported as well. The resulting defects are either collision cascades, originating from fast neutrons (E > 0.1 MeV), or point defects, originating from neutrons with lower energies. Their influence on J(c) will be discussed
Performance review of the joints for the ITER poloidal field coils
Get PDFFor large scale magnets wound with cable-in-conduit conductors, the safe operation of the joints is of paramount importance to guarantee adequate reliability and stability margin of the whole magnet. For this reason, during the R&D activities undertaken for the development of the ITER magnet system, several experimental campaigns were launched to study the AC and DC performance of the joint and limit the risk of thermal runaways at the joints during the tokamak operation. The joint electrical resistance must be limited below specified values to avoid excessive heating generated by the transport current. Moreover, in presence of time-varying fields, different types of losses arise at the joints, which can be associated to their superconducting and resistive parts. The relative importance of these losses depends on the joint manufacturing solution. The aim of this investigation is to analyze the performance at different working conditions of the joints for the connection of the conductors of the poloidal field (PF) coils of the ITER magnet system. This work presents, for the first time, a wide review of the test campaign performed from 2016 to 2021 on the PF joint samples during the three manufacturing phases, namely pre-qualification, qualification and production. The values of electrical resistances and losses under sinusoidal field variations are reported in the paper at different operating conditions, thus building a useful database to assess the joint performances during the machine operation. The data here collected show the impact of the manufacturing techniques on the joint performances and, furthermore, represent a useful tool for the validation of numerical and analytical models of joints
Multiphysics Model of Quench for the ITER Central Solenoid
Get PDFThe ITER Central Solenoid (CS), the backbone of the ITER magnet system, is composed of 6 modules, each made of 40 pancakes, for a total conductor length of about 36 km. More than 4 km of pipes, about 30 bypass or control valves, the heat exchangers and a cold circulator are part of the cryogenic distribution used to maintain the nominal operating conditions (flow and temperature). During the plasma scenario, several loss sources - such as AC losses, heat from supports and structures, joule heating at joints - can affect the magnet stability. A reliable analysis of quench is therefore of great importance to guarantee the safe operation of the CS superconducting coils. In this work, the SuperMagnet code, a state of the art software for the numerical modelling of hydraulic, electrical and thermal phenomena occurring in superconducting magnets, is applied to study the CS and its cryogenic distribution during quench events
Variations 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
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
- …
