1,720,973 research outputs found
Modal analysis of the fields in the ITER ICRF antenna port plug cavity
Full text linkThe cavity that is formed between the ITER ICRF antenna plug and its port can exhibit resonances at specific fre-quencies, some of them in the relevant range of frequencies for IC heating. These resonances related to eigenmodes of the coaxial cavity, can substantially increase the level of electric fields inside the cavity and the level of RF losses in the B4C neutron shielding tiles at the back of the port-plug cavity can also be significant. For instance, in MWS simulations of a simplified geometry of the antenna in front of a dielectric mimicking the plasma loading, the level of RF losses in the B4C can reach tens of kW in 00ππ toroidal phasing and even larger values in monopole. RF probes will be installed to monitor the RF fields in the port plug cavity and additional simulations are required to properly assess the integration (position, orientation) and their effectiveness. A model with a very detailed geometry of the antenna was also used in Ansys HFSS and TOPICA simulations. On the one hand it is observed that the resistivity of the B4C neutron shielding material located at the back of the cavity has a marked effect on the excitation of the resonances and that for certain ranges of resistivity the numerical computation fails exhausting computer memory requirements (Ansys/HFSS) when trying to solve the total antenna and cavity problem as a single model. On the other hand lossy materials such as the B4C tiles cannot be represented in TOPICA models while a realistic plasma gyrotropic load can not be simulated in HFSS/MWS. Therefore, we introduced a modal analysis in the cavity to decouple solving the computationally intensive plasma-facing front of the launcher from the cavity. The fields computed by TOPICA for various loading conditions and frequencies are evaluated on a set of vertical planes in the cavity and expanded in a series of modal eigenmodes for a given mode of operation. This provides the necessary input for an accurate evaluation of the RF fields in the cavity in an independent model not including the antenna front-face. It will also contribute to the understanding of the impact of the relative toroidal phasing of the strap currents on the excitation of the cavity modes and to simulate accurately the response of the cavity RF probes
Progress in the analysis of the cavity resonances in the ITER ICRF antenna port plug
Full text linkThe ITER ICRF antenna plug [1, 2] can exhibit resonances at specific frequencies, some of them in the relevant range of frequencies for IC heating. These resonances have been identified as eigenmodes of the coaxial cavity, where the array plays the role of inner conductor [3], that can substantially increase the level of electric fields within the cavity as well as the level of RF losses. As no grounding solution is considered, RF probes should be installed to monitor the RF fields in the port plug cavity and additional simulations of a realistic magnetized plasma are required to properly assess the integration (position, orientation) and their effectiveness. Several numerical tools are available and have been extensively used to simulate the ITER ICRF antenna, such as TOPICA [5] or CST Microwave Studio (MWS [6]), but none of these codes allow to combine realistic geometries, realistic magnetized plasma profiles, and lossy materials. In this paper we pursue the effort started in [8] where a method based on a modal analysis in the cavity was introduced to decouple solving the computationally intensive plasma facing front of the launcher from the cavity. The method reproduces the TOPICA electric fields (with gyrotropic plasma effects) obtained in a given vertical reference plane, in a MWS cavity (including lossy materials) using the multimodal scattering matrix of the cavity obtained with MWS. This method is here applied to several realistic ITER plasma profiles. The recently extracted magnetic fields [9] from the TOPICA modeling results, provide an alternate way to compute the excitation spectrum of the cavity and therefore allow to confirm our results. Accurate levels of RF losses can then be obtained from various plasma profiles and excitation of the antenna straps
Radar arc and impairment detection and localization for the ITER ICRF antenna
Full text linkA RAdar Arc and impairments Detection and localization (RAAD) system for the protection of high-power RF transmission lines components is presented. It offers several benefits over existing techniques. It can perform fast detection, localization, and classification of arcs and impairments/degradations along the full path of the RF power (in less than 5 μs as required for the protection of ITER ICRF antenna). It also features completely independent operations from the RF power. The detection and monitoring of impairments/degradations enables the prevention of faults while the localization and classification of faults permits pinpoint maintenance operations. The RAAD system has been simulated in time domain adopting the Simulink tool, integrated into the complete ITER ICRF system (from the array antenna front-face up to the RF sources outputs, including the full transmission line and matching network). The radar signal is coupled into the transmission lines through a specifically designed coupling unit. Full wave simulations of the ITER ICRF system components have been performed in the radar bandwidth of operation, with and without arcs/impairments, to obtain S-matrices used in the time domain radar system simulations. All the arcs and impairments inserted in the components have been detected; the location obtained by the radar for each event has been compared to the one estimated analytically with excellent agreement. The radar simulations have demonstrated the ability to detect and localize arcs which cannot be detected by other systems such as low voltage arcs and series arcs. A solid solution, based on signal synchronization, for coping with high power interferences from ion cyclotron frequency harmonics in the radar bandwidth of operations has been implemented. Other events such as antenna load variations and matching elements modifications can be easily discriminated against arc events, being much slower than radar pulse repetition period. Next steps will be the implementation, testing and validation of a prototype of the complete RAAD system. This prototype will be tested on the ITER ICRF prototype antenna module and potentially on other operating ICRF installations
Full-wave modeling of arcs within the ITER ICRF antenna for usage in the simulations and design of the RADAR Arc Detection system
Full text linkThe ITER ICRF antenna [1] has been carefully designed to feature electrical fields below tolerable limits (typically, below 2 or 3 kV/mm depending on the location and orientation) when operating at a maximum voltage of 45 kV. In particular, this allows avoiding arcs. However, as for any high-power RF system, arcs can still occur in the ICRF antenna and its power feeding system, during normal operation and especially during the commissioning. Whenever an arc is detected, the RF power shall be immediately tripped (μs timescale) to avoid strong local energy deposition at the location of the arc. Undetected arcs are forbidden. To this aim, several complementary and redundant Arc Detection (AD) systems are foreseen to protect the ITER ICRF antenna. Among these AD systems is the RADAR Arc Detection (or RAAD [2]) which is currently under evaluation for implementation on the ITER ICRF system To provide a first numerical proof of concept of RAAD, full-wave simulations of the ITER ICRF antenna and its power feeding transmission lines have been performed in the radar bandwidth of operation (up to ~ 350 MHz) with the help of CST Studio Suite and ANSYS HFSS commercial codes. In these simulations, the plasma loading has been approximated by a salty water load (with a relative dielectric permittivity εr = 80 and electrical conductivity σ = 1 S/m), while arcs have been modelled with both perfect electric conductor (PEC) cylinders or lumped element shorts. The obtained S-matrices have been then loaded and processed by the RAAD time-domain circuit simulations and signal processing calculations 2. This paper describes the challenges to simulate the full ITER ICRF antenna with arcs, considering different loading conditions, different materials and different solutions for the arc insertion. It also provides a comparison of the scattering parameters with and without arcs
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
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