Recent analysis of the ITER ion cyclotron antenna with the TOPICA code

Plasma heating in the Ion Cyclotron Range of Frequencies (ICRF) is adopted in most of the existing nuclear fusion experiments and is also one of the three auxiliary heating systems of ITER. Two identical ICRF antennas will be installed in ITER with the aim of delivering 10MW per antenna to the plasma for the baseline design configuration (upgradable to 20 MW/antenna). In order to optimize the feeding circuit and to evaluate and predict the overall performances of an ICRF launcher it is fundamental to perform radio-frequency simulations of the antenna detailed geometry loaded with a realistic plasma, and to extract the antenna input parameters, the electric current on conductors and the radiated field. In this work, we analyze the current ITER ICRF launcher, for the first time including the surrounding cavity between the port plug and the port extension, and a portion of the blanket tiles in the TOPICA code; the geometrical description of the antenna has reached an unprecedented level of accuracy. The ITER ICRF antennas have been the object of a comprehensive analysis, varying the working frequency, the plasma conditions and the poloidal and toroidal phasings between the feeding transmission lines. The performances of the antennas have been documented in terms of input parameters, power coupled to plasma and electric fields, for a reference set of ITER plasma equilibria and assuming a maximum voltage on the system

Réalisation d'un capteur d'images matriciel avec sortie numérique

Cet article présente un prototype de capteur d'images conçu au laboratoire LE2I du Creusot. Il est réalisé sous la forme d'un ASIC en technologie Cmos 1.0mm. Il est destiné à être utilisé en contrôle qualité par vision artificielle pour des scènes présentant de forts contrastes lumineux. Un procédé original de numérisation du niveau de gris permet de contourner la notion classique de temps d'exposition variable et de traiter aisément les problèmes d'éblouissement local. Il permet également d'ouvrir de larges perspectives dans le domaine des capteurs intelligents, en effet la numérisation de l'information au niveau même du photosite permet, à terme d'envisager l'intégration d'un classifieur dans le voisinage immédiat du pixel, et de fournir une décision binaire en sortie du capteur

Recent modeling for the ITER ion cyclotron range of frequency antennas with the TOPICA code

This paper documents the analysis of the ITER ion cyclotron resonance heating (ICRF) launcher using the TOPICA code, throughout recent years' design activities. The ability to simulate the detailed geometry of an ICRF antenna in front of a realistic plasma and to obtain the antenna input parameters, the electric currents on conductors and the radiated field distribution next to the antenna is of significant importance to evaluate and predict the overall system performances. Starting from a reference geometry, we first investigated the impact of some geometrical and numerical factors, such as the Faraday Screen geometry or the mesh quality. Then a final geometry was the object of a comprehensive analysis, varying the working frequency, the plasma conditions and the poloidal and toroidal phasings between the feeding lines. The performance of the antenna has been documented in terms of input parameters, power coupled to plasma and electric fields. Eventually, the four-port junction has also been included in TOPICA models

Control of neoclassical tearing modes by Sawtooth control

The onset of a neoclassical tearing mode (NTM) depends on the existence of a large enough seed island. It is shown in the Joint European Torus that NTMs can be readily destabilized by long-period sawteeth, such as obtained by sawtooth stabilization from ion-cyclotron heating or current drive. This has important implications for burning plasma scenarios, as alpha particles strongly stabilize the sawteeth. It is also shown that, by adding heating and current drive just outside the inversion radius, sawteeth are destabilized, resulting in shorter sawtooth periods and larger beta values being obtained without NTMs

Heating, current drive and energetic particle studies on JET in preparation of ITER operation

This paper summarizes the recent work on JET in the three areas of heating, current drive and energetic particles. The achievements have extended the possibilities of JET, have a direct connection to ITER operation and provide new and interesting physics. Toroidal rotation profiles of plasmas heated far off axis with little or no refuelling or momentum input are hollow with only small differences on whether the power deposition is located on the low field side or on the high field side. With LH current drive the magnetic shear was varied from slightly positive to negative. The improved coupling (through the use of plasma shaping and CD4) allowed up to 3.4 MW of PLH in internal transport barrier (ITB) plasmas with more than 15 MW of combined NBI and ICRF heating. The q-profile with negative magnetic shear and the ITB could be maintained for the duration of the high heating pulse (8 s). Fast ions have been produced in JET with ICRF to simulate alpha particles: by using third harmonic 4He heating, beam injected 4He at 120 kV were accelerated to energies above 2 MeV, taking advantage of the unique capability of JET to use NBI with 4He and to confine MeV class ions. ICRF heating was used to replicate the dynamics of alpha heating and the control of an equivalent Q = 10 `burn' was simulated

Functional MRI evidence for the decline of word retrieval and generation during normal aging

International audienceThis fMRI study aimed to explore the effect of normal aging on word retrieval and generation. The question addressed is whether lexical production decline is determined by a direct mechanism, which concerns the language operations or is rather indirectly induced by a decline of executive functions. Indeed, the main hypothesis was that normal aging does not induce loss of lexical knowledge, but there is only a general slowdown in retrieval mechanisms involved in lexical processing , due to possible decline of the executive functions. We used three tasks (verbal fluency, object naming , and semantic categorization). Two groups of participants were tested (Young, Y and Aged, A), without cognitive and psychiatric impairment and showing similar levels of vocabulary. Neuropsychological testing revealed that older participants had lower executive function scores, longer processing speeds, and tended to have lower verbal fluency scores. Additionally, older participants showed higher scores for verbal automa-tisms and overlearned information. In terms of behav-ioral data, older participants performed as accurate as younger adults, but they were significantly slower for the semantic categorization and were less fluent for verbal fluency task. Functional MRI analyses suggested that older adults did not simply activate fewer brain regions involved in word production, but they actually showed an atypical pattern of activation. Significant correlations between the BOLD (Blood Oxygen Level Dependent) signal of aging-related (A > Y) regions and cognitive scores suggested that this atypical pattern of the activation may reveal several compensatory mechanisms (a) to overcome the slowdown in retrieval, due to the decline of executive functions and processing speed and (b) to inhibit verbal automatic processes. The BOLD signal measured in some other aging-dependent regions did not correlate with the behavioral and neuro-psychological scores, and the overactivation of these uncorrelated regions would simply reveal dedifferentia-tion that occurs with aging. Altogether, our results suggest that normal aging is associated with a more difficult access to lexico-semantic operations and representations by a slowdown in executive functions, without any conceptual loss