Modeling of tungsten melt layer erosion caused by JxB force at TEXTOR with the code MEMOS

Tungsten in form of macrobrush is foreseen as one of candidate materials for the ITER divertor. Melting of tungsten, the melt motion, and melt splashing are expected to be the main mechanisms of a surface damage determining the lifetime of plasma facing components. Experiments with the long-time plasma action at the metalic surface in a strong magnetic field demonstrated that the JxB force generated by the thermo-emission electrons dominates in the acceleration of the melt layer and leads to a high target damage. In the paper numerical simulation model implemented into the code MEMOS is described and modelling of tungsten target damage caused by the long-time plasma heat loads supporting the TEXTOR experiments are performed with 3D version of the code MEMOS. Calculated damages of tungsten targets are in a reasonable agreement with the target damages observed in the TEXTOR experiments that allows projections upon the surface damage at ITER and DEMO conditions.Вольфрам в виде макробрашей рассматривается в качестве основного материала для дивертора ИТЭРа. Плавления вольфрама, движение и разбрызгивание расплава рассматриваются в качестве основных механизмов повреждения поверхности, которые определяют время жизни элементов дивертора. Эксперименты с длительным воздействием плазмы на металлические поверхности в сильном магнитном поле показали, что JxB-сила, генерируемая термоэмиссией электронов, доминирует в ускорении слоя расплава и приводит к большому повреждению поверхности. Описана численная модель моделирования эрозии металлической поверхности при плазменном воздействии, имплементированная в код MEMOS. Приведены результаты моделирования эрозии вольфрамовой мишени, вызванной длительным воздействием плазмы в экспериментах в TEXTORе, проведенного 3D-версией кода MEMOS. Расчетная эрозия вольфрама находится в разумном согласии с эрозией вольфрамового лимитера, которая наблюдалась в экспериментах в TEXTORе. Данные расчета позволяют делать прогнозы относительно эрозии поверхности в условиях ИТЭР и ДЕМО.Вольфрам у вигляді макробрашів розглядається в якості основного матеріалу для дивертора ІТЕРа. Плавлення вольфраму, рух і розбризкування розплаву розглядаються в якості основних механізмів пошкодження поверхні, що визначають час життя елементів дивертора. Експерименти з тривалим впливом плазми на металеві поверхні в сильному магнітному полі показали, що JxB-сила, що генерується термоемісією електронів, домінується в прискоренні шару розплаву і приводить до великих пошкоджень поверхні. Описана чисельна модель моделювання ерозії металевої поверхні при плазмовому впливі, імплементована в код MEMOS. Наведено результати моделювання ерозії вольфрамової мішені, викликаної тривалим впливом плазми в експериментах в TEXTORі, проведенного 3D-версією коду MEMOS. Розрахункована ерозія вольфраму знаходиться в розумній згоді з ерозією вольфрамового лімітера, яка спостерігалася в експериментах в TEXTORі. Дані розрахунку дозволяють робити прогнози, щодо ерозії поверхні в умовах ІТЕР і ДЕМО

Heat flux analysis of Type-I ELM impact on a sloped, protruding surface in the JET bulk tungsten divertor

Tungsten (W) melting due to transient power loads, for example those delivered by edge localised modes (ELMs), is a major concern for next step fusion devices. A series of experiments has been performed on JET to investigate the dynamics of Type-I ELM-induced transient melting. Following initial exposures in 2013 of a W-lamella with sharp leading edge in the bulk W outer divertor, new experiments have been performed in 2016-2017 on a protruding W-lamella with a 15 degrees slope, allowing direct and spatially resolved (0.85 mm/pixel) observation of the top surface using the IR thermography system viewing from the top of the poloidal cross-section. Thermal and IR analysis have already been conducted assuming the geometrical projection of the parallel heat flux on the W-lamellas, thus ignoring the gyro-radius orbit of plasma particles. Although it is well justified during L-mode or inter-ELM period, the hypothesis becomes questionable during ELM when the ion Larmor radius is larger. The goal of this paper is to extend the previous analysis based on the forward approach to the H-mode discharges and investigate in particular the gyro-radius effect during the Type-I ELMs, those used to achieve transient melting on the slope of the protruding W-lamella. Surface temperatures measured by the IR camera are compared with reconstructed synthetic data from 3D thermal modelling using heat loads derived from optical projection of the parallel heat flux (ignoring the gyro-radius orbit), 2D gyro-radius orbit and particle-in-cell (PIC) simulations describing the influence of finite Larmor-radius effects and electrical potential on the deposited power flux. Results show that the ELM power deposition behaves differently than the optical projection of the parallel heat flux, contrary to the L-mode observations, and may thus be due to the much larger gyro-orbits of the energetic ELM ions in comparison to L-mode or inter-ELM conditions.EURATOM 63305

Tungsten fibre-reinforced composites for advanced plasma facing components

AbstractThe European Fusion Roadmap foresees water cooled plasma facing components in a first DEMO design in order to provide enough margin for the cooling capacity and to only moderately extrapolate the technology which was developed and tested for ITER. In order to make best use of the water cooling concept copper (Cu) and copper-chromium-zirconium alloy (CuCrZr) are envisaged as heat sink whereas as armour tungsten (W) based materials will be used. Combining both materials in a high heat flux component asks for an increase of their operational range towards higher temperature in case of Cu/CuCrZr and lower temperatures for W. A remedy for both issues- brittleness of W and degrading strength of CuCrZr- could be the use of W fibres (Wf) in W and Cu based composites. Fibre preforms could be manufactured with industrially viable textile techniques. Flat textiles with a combination of 150/70 µm W wires have been chosen for layered deposition of tungsten-fibre reinforced tungsten (Wf/W) samples and tubular multi-layered braidings with W wire thickness of 50 µm were produced as a preform for tungsten-fibre reinforced copper (Wf /Cu) tubes. Cu melt infiltration was performed together with an industrial partner resulting in sample tubes without any blowholes. Property estimation by mean field homogenisation predicts strongly enhanced strength of the Wf/CuCrZr composite compared to its pure CuCrZr counterpart. Wf /W composites show very high toughness and damage tolerance even at room temperature. Cyclic load tests reveal that the extrinsic toughening mechanisms counteracting the crack growth are active and stable. FEM simulations of the Wf/W composite suggest that the influence of fibre debonding, which is an integral part of the toughening mechanisms, and reduced thermal conductivity of the fibre due to the necessary interlayers do not strongly influence the thermal properties of future components

Transthoracic 3D echocardiographic left heart chamber quantification in patients with bicuspid aortic valve disease

Integration of volumetric heart chamber quantification by 3D echocardiography into clinical practice has been hampered by several factors which a new fully automated algorithm (Left Heart Model, (LHM)) may help overcome. This study therefore aims to evaluate the feasibility and accuracy of the LHM software in quantifying left atrial and left ventricular volumes and left ventricular ejection fraction in a cohort of patients with a bicuspid aortic valve. Patients with a bicuspid aortic valve were prospectively included. All patients underwent 2D and 3D transthoracic echocardiography and computed tomography. Left atrial and ventricular volumes were obtained using t

Qualitative grading of aortic regurgitation: a pilot study comparing CMR 4D flow and echocardiography

Over the past 10 years there has been intense research in the development of volumetric visualization of intracardiac flow by cardiac magnetic resonance (CMR). This volumetric time resolved technique called CMR 4D flow imaging has several advantages over standard CMR. It offers anatomical, functional and flow information in a single free-breathing, ten-minute acquisition. However, the data obtained is large and its processing requires dedicated software. We evaluated a cloud-based application package that combines volumetric data correction and visualization of CMR 4D flow data, and assessed its accuracy for the detection and grading of aortic valve regurgitation using transthoracic echocardiography as reference. Between June 2014 and January 2015, patients planned for clinical CMR were consecutively approached to undergo the supplementary CMR 4D flow acquisition. Fifty four patients (median age 39 years, 32 males) were included. Detection and grading of the aortic valve regurgitation using CMR 4D flow imaging were evaluated against transthoracic echocardiography. The agreement between 4D flow CMR and transthoracic echocardiography for grading of aortic valve regurgitation was good (κ = 0.73). To identify relevant, more than mild aortic valve regurgitation, CMR 4D flow imaging had a sensitivity of 100 % and specificity of 98 %. Aortic regurgitation can be well visualized, in a similar manner as transthoracic echocardiography, when using CMR 4D flow imaging

Plasma–wall interaction studies within the EUROfusion consortium : progress on plasma-facing components development and qualification

The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful o peration of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading f acilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualificat ion and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma–material interaction as well as the study of fundamental processes. WP PFC addresses these c ritical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle lo ads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alter native scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and m icrostructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.Peer reviewe

Pulsar polarisation below 200 MHz: Average profiles and propagation effects

Aims: We present the highest-quality polarisation profiles to date of 16 non-recycled pulsars and four millisecond pulsars, observed below 200 MHz with the LOFAR high-band antennas. Based on the observed profiles, we perform an initial investigation of expected observational effects resulting from the propagation of polarised emission in the pulsar magnetosphere and the interstellar medium. Methods: The polarisation data presented in this paper have been calibrated for the geometric-projection and beam-shape effects that distort the polarised information as detected with the LOFAR antennas. We have used RM Synthesis to determine the amount of Faraday rotation in the data at the time of the observations. The ionospheric contribution to the measured Faraday rotation was estimated using a model of the ionosphere. To study the propagation effects, we have compared our low-frequency polarisation observations with archival data at 240, 400, 600, and 1400 MHz. Results: The predictions of magnetospheric birefringence in pulsars have been tested using spectra of the pulse width and fractional polarisation from multifrequency data. The derived spectra offer only partial support for the expected effects of birefringence on the polarisation properties, with only about half of our sample being consistent with the model's predictions. It is noted that for some pulsars these measurements are contaminated by the effects of interstellar scattering. For a number of pulsars in our sample, we have observed significant variations in the amount of Faraday rotation as a function of pulse phase, which is possibly an artefact of scattering. These variations are typically two orders of magnitude smaller than that observed at 1400 MHz by Noutsos et al. (2009), for a different sample of southern pulsars. In this paper we present a possible explanation for the difference in magnitude of this effect between the two frequencies, based on scattering. Finally, we have estimated the magnetospheric emission heights of low-frequency radiation from four pulsars, based on the phase lags between the flux-density and the PA profiles, and the theoretical framework of Blaskiewicz et al. (1991, ApJ, 370, 643). These estimates yielded heights of a few hundred km; at least for PSR B1133+16, this is consistent with emission heights derived based on radius-to-frequency mapping, but is up to a few times larger than the recent upper limit based on pulsar timing. Conclusions: Our work has shown that models, like magnetospheric birefringence, cannot be the sole explanation for the complex polarisation behaviour of pulsars. On the other hand, we have reinforced the claim that interstellar scattering can introduce a rotation of the PA with frequency that is indistinguishable from Faraday rotation and also varies as a function of pulse phase. In one case, the derived emission heights appear to be consistent with the predictions of radius-to-frequency mapping at 150 MHz, although this interpretation is subject to a number of systematic uncertainties