COVID-19 Containment Measures at Childcare and Schools in 19 European Countries:An Observational Study on Local, Federal and National Policies

Objectives: After childcare and schools have been closed in March 2020 to prevent the spread of COVID-19, they were open again in most European countries after the summer holidays till early autumn. Aim of this study is to give an overview and to compare COVID-19 childcare and school containment policies in 19 European countries. Methods: We collected data on containment measures among delegates of the European Academy of Pediatrics (EAP), through an online, closed questionnaire in the second half of October 2020. Results: Most policy has been formulated for secondary education. In all three settings policy was most often formulated for individual hygiene, cleaning of surfaces, exclusion of sick children, ventilation, distance between children and between children and teachers. In secondary schools, policy is formulated on face masks in and outside the class. School closure, cancellation of physical education and class size reduction are measures for which the fewest countries have formulated national policies. Conclusion: We recommend to accompany the opening of children’s facilities and schools by surveillance studies that further clarify questions about control measures implemented to halt COVID-19 pandemic

Multifaceted Simulations Reproducing Experimental Results from the 1.5-MW 140-GHz Preprototype Gyrotron for W7-X

A multifaceted simulation procedure, addressing the electron beam properties, the beam-wave interaction, and the internal losses, has been used for the simulation of the experimental operation of a 1.5-MW 140-GHz short-pulse preprototype gyrotron. The preprototype is related to the development of 1.5-MW gyrotrons for the upgrade of the electron cyclotron resonance heating system at the stellarator W7-X. A very good reproduction of experimental results has been achieved by simulation, without resorting to arbitrary speculations. This validated the numerical tools as well as the design and fabrication of the short-pulse preprototype, which fully reached the target of efficient 1.5-MW operation in millisecond pulses. Special attention has been given to simulating the possibility of parasitic after-cavity interaction in the gyrotron launcher. Also, parasitic backward-wave excitation in the gyrotron cavity has been demonstrated by simulation, at a frequency and voltage range in agreement with experimentally observed parasitic oscillations. This offers an additional possibility with respect to the origin of deleterious parasitic oscillations in high-power gyrotrons, which are usually attributed mainly to the gyrotron beam tunnel

Investigation of a Mini-Channel Cavity Cooling Concept for a 170 GHz, 2 MW Coaxial-Cavity Gyrotron

The maximum heat load on the cavity wall of high power fusion gyrotrons is one of the major limiting technological factors for the operation of the tube. To achieve the requested output power, efficiency and pulse length, a very efficient cooling of the interaction structure is mandatory. In this work, the performance of a mini-channel cavity cooling system for a 170 GHz, 2 MW coaxial-cavity gyrotron is numerically investigated, including the development of a mock-up test set-up for experimental validation

Design of MW-Class Coaxial Gyrotron Cavities With Mode-Converting Corrugation Operating at the Second Cyclotron Harmonic

This article presents investigations on the design of coaxial gyrotron cavities with mode-converting corrugations, operating at the second harmonic of the electron cyclotron frequency with output power of the order of megawatts. The suppression of the competing modes interacting at the fundamental cyclotron frequency is achieved by the combination of a corrugated coaxial insert and mode-converting corrugation on the outer wall. The outer corrugation couples the key competing modes to lower order modes with reduced quality factor. The design steps, which form a generally applicable design procedure, are described in detail. As an illustrative example, the proposed procedure is used for the design of a cavity for a fusion-relevant, second-harmonic MW-class gyrotron, operating at 170 GHz with the TE 37,1837,18 mode. From the simulations, it is found that for the proposed design, this mode is excited with an output power of around/ ∼ 1.5 MW. Two additional paths for cavity optimization toward even higher output power are also presented

Generation of 1.5MW-140GHz pulses with the modular pre-prototype gyrotron for W7-X

In anticipation of an Electron Cyclotron Resonance Heating system upgrade for the stellarator Wendelstein 7-X, a 1.5 MW – 140 GHz continuous-wave gyrotron is under development. In order to provide a first experimental verification of the scientific RF and electron beam optics design of the gyrotron with ms pulses, the Karlsruhe Intitule of Technology has developed a short-pulse pre-prototype gyrotron. In this work, we present details regarding the construction of the pre-prototype as well as measurements from the first experimental campaign delivering up to 1.6 MW in short pulses

Etude du comportement paramagnétique des actinides (IV) (Th, U, Np et Pu) en solution en présence de ligands

International audienceLa spectroscopie RMN est une technique capable de fournir des informations structurales sur des complexes métalliques en solution. Elle peut être appliquée à l’analyse de petites molécules en chimie organique, de protéines (macros molécules) en biologie mais aussi en chimie nucléaire avec la nucléarisation des spectromètres [1]. La présence d’un Actinide (An), avec des électrons 5f non appariés, génère une modification du spectre RMN (un élargissement et/ou une variation du déplacement chimique des pics) caractéristique du paramagnétisme du cation.Dans le cas des complexes paramagnétiques de Ln$^{III}$ (éléments 4$f$), le déplacement chimique total $\Delta _{TOT}$ est modélisé par l’équation de Bleaney (équations (a) et (b)) [2]. Il dépend du déplacement chimique paramagnétique induit $\delta _{para}$ qui peut être décomposé en deux contributions : un terme de contact $\delta _{cont}$ (délocalisation de l’électron $f$ sur l’atome donneur du ligand) et un terme dipolaire $\delta _{dip}$ (interaction entre le spin électronique et nucléaire à travers l’espace). A partir de ce dernier terme, on peut déduire des informations structurales en utilisant les constantes de Bleaney

Overview of KIT activities on high power, high frequency gyrotron development and the role of the new FULGOR teststand at KIT

For a future DEMOnstration fusion power plant two challenging trends with respect to gyrotron features are recognized: (a) the operating frequency will be above 200 GHz and (b) the requested total efficiency of the gyrotron should be as high as possible. ECRH systems for future plants (DEMO) or Fusion Power Plants (FPP) will most probably require multi-megawatt and continuous wave gyrotrons which are able to oscillate at a frequency significantly above 200 GHz. The coaxial cavity technology which is under investigation and development at KIT since several years, seems to have the optimum properties to fulfill the requirements towards sub-THz operation in the MW output power regime. To benefit from these advantages and to profit from the existing experience on this technology the modular 2 MW 170 GHz gyrotron has been taken as a starting point for a 170/204/238 GHz multi-frequency gyrotron design study. Recent activities for improvement of the performance of this gyrotron and preparations for long pulse operation will be shown. In a first step we aim at ~ 100 ms operation, in a second step, with the tube being equipped with an improved cooling system, 1 s operation is envisaged. KIT is currently constructing a new gyrotron teststand, FULGOR, having specific features, such as: 10 MW electrical input power in CW, magnetic field up to 10.5 T with 261 mm warm bore hole of the SCM and several voltage taps from the high-voltage DC power supply. The CW HV Power supply (120 kV, 130 A) has already been delivered and accepted, a dry superconducting magnet will be delivered in 2019. For the first time it will be possible with FULGOR to test Multistage Depressed Collector (MDC) gyrotrons which are supposed to increase the overall efficiency from 50 % (state of the art) to 60 % or even higher. There are two concepts for gyrotron MDC: a axisymmetric concept, which relies on the demagnetization combined with non-adiabatic magnetic transitions and a concept based on E×B drifts to sort electrons. First considerations of a proof-of-principle design for the ExB drift concept will be shown

Calibration of the KIT test setup for the cooling tests of a gyrotron cavity full-size mock-up equipped with mini-channels

In high-power fusion gyrotrons, the maximum heat-load on the wall of the interaction section is in the order of 2 kW/cm2, which is the major limiting technological factor for output power and pulse-length of the tube. The ongoing gyrotron development demands a very effective cavity cooling system for optimum gyrotron operation. In this work, the experimental investigation of a mini-channel cavity cooling using a mock-up test set-up is described. The mock-up test set-up will be used to experimentally validate the predictive simulation results and verify the mini-channel cooling performance. It is crucial for validation of the mini-channel cooling properties to determine the amount of the heat load introduced in the cavity wall by an induction heater. In order to estimate that heat load, full 3D electromagnetic simulations have been performed using the CST Studio Suite® software. A suitable calibration factor for the load deposited in the mock-up inner wall is identified after numerical investigation by a 3D thermal model. Calorimetry measurements are performed and the experimental results are compared with the simulation results obtained with a 3D thermal-hydraulic model, using the commercial software STAR-CCM+. When the calibration factor is applied, the experimental calorimetry is well reproduced by the simulations