Overview of core impurity transport in the first divertor operation of Wendelstein 7-X

The impurity transport at Wendelstein 7-X during its most recent campaign is characterized and documented for a variety of different plasma scenarios. An overview of its dependence on several quantities is given, which allows identification of transport regimes and the major driver for impurity transport. Beyond this, a comparison with the impurity behavior in other fusion devices is now possible. In contrast to other stellarators, no density dependence of the impurity transport has been found. Additionally, the influence of the turbulence contribution to the overall transport is reflected in the dependence on various parameters, e.g. turbulent diffusion and density fluctuation amplitudes. With this database approach, one can now also apply scaling laws to make extrapolations about the impurity confinement in future plasma scenarios

W7-X plasma diagnostics for impurity transport studies

The Wendelstein 7-X (W7-X) stellarator which is located in Greifswald, Germany is an experimental device for demonstration of steady-state plasma operation. It was commissioned at the end of 2015 and at the beginning, it was operated in the limiter configuration (5 poloidal uncooled graphite limiters) while starting from 2017 it has been equipped with a carbon uncooled divertor. With the launch of the device, new diagnostics have also been commissioned and tested. Understanding of impurity transport in stellarators is a crucial task in the optimisation process. At W7-X there are several spectroscopic systems which deliver information about plasma impurities. One of them is a pulse height analysis system (PHA) which collects soft X-ray spectra in the energy range from about 300 eV up to 20 keV with 100 ms temporal resolution. There are also X-ray imaging spectrometers XICS and HR-XIS which are devoted for measurements of spatio-temporal impurity emissivity of highly ionized ions with high temporal resolution (5 ms). Spectra in the VUV region are measured by the High-Efficiency XUV Overview Spectrometer (HEXOS).Стеларатор Wendelstein 7-X (W7-X), який розташований в Грайфсвальді, Німеччина, є експериментальною установкою для демонстрації стаціонарного утримання плазми. Стеларатор було введено в експлуатацію в кінці 2015 року та спочатку експлуатувався в конфігурації з обмежувачем (5 полоідальних неохолоджуваних графітових обмежувачів). З 2017 року установка була оснащена вуглецевим неохолоджуваним дивертором. Із запуском стеларатора були також введені в експлуатацію і випробувані нові діагностичні системи. Розуміння транспорту домішок y стелараторі є важливим завданням для оптимізації його роботи. На W7-X є декілька спектроскопічних систем, які надають інформацію про домішки в плазмі. Одна з них – система аналізу висоти спостережуваного імпульсу (PHA) – реєструє спектри м'якого рентгенівського випромінювання в діапазоні енергій від близько 300 еВ до 20 кеВ з часовою роздільною здатністю 100 мс. Є також рентгенографічні спектрометри XICS і HR-XIS, призначені для виміру просторово-часової випромінювальної здатності домішок, геліоподібних іонів з високою часовою роздільною здатністю (5 мс). Спектри в області VUV вимірюють за допомогою високоефективного оглядового спектроаналізатора (HEXOS).Стелларатор Wendelstein 7-X (W7-X), который расположен в Грайфсвальде, Германия, является экспериментальной установкой для демонстрации стационарного удержания плазмы. Стелларатор был введен в эксплуатацию в конце 2015 года, и вначале эксплуатировался в конфигурации с ограничителем (5 полоидальных неохлаждаемых графитовых ограничителей). С 2017 года установка оснащена углеродным неохлаждаемым дивертором. С запуском стелларатора были также введены в эксплуатацию и испытаны новые диагностические системы. Понимание транспорта примесей в стеллараторе является важной задачей для оптимизации его работы. На W7-X имеется несколько спектроскопических систем, которые предоставляют информацию о примесях в плазме. Одна из них – система анализа высоты наблюдаемого импульса (PHA) – регистрирует спектры мягкого рентгеновского излучения в диапазоне энергий от около 300 эВ до 20 кэВ с временным разрешением 100 мс. Имеются также рентгенографические спектрометры XICS и HR-XIS, предназначенные для измерения пространственновременной примесной излучательной способности гелиоподобных ионов с высоким временным разрешением (5 мс). Спектры в области VUV измеряют с помощью высокоэффективного обзорного спектроанализатора (HEXOS)

Quantitative comparison of impurity transport in turbulence reduced and enhanced scenarios at Wendelstein 7-X

We assess the turbulent particle transport being responsible for the limitation of the confinement and, thus, the overall performance of the neoclassically optimized stellarator Wendelstein 7-X. The radial particle transport is experimentally inferred from the evaluation of impurity injection into turbulence reduced and enhanced plasma scenarios revealing a completely different confinement behavior. The impact of the density gradient on the turbulent ion transport is theoretically estimated using large-scale non-linear gyro-kinetic simulations enabling, for the first time in Wendelstein 7-X, a quantitative comparison to the experimentally assessed impurity transport properties. We demonstrate that impurity transport in most of the Wendelstein 7-X discharges, up to now impossible to cover only with neoclassical estimations, is dominated by turbulence and can be modelled via gyro-kinetic simulations

Preparation, analysis, and application of coated glass targets for the Wendelstein 7-X laser blow-off system

Coated glass targets are a key component of the Wendelstein 7-X laser blow-off system that is used for impurity transport studies. The preparation and analysis of these glass targets as well as their performance is examined in this paper. The glass targets have a high laser damage threshold and are coated via physical vapor deposition with μm thick films. In addition, nm-thin layers of Ti are used as an interface layer for improved ablation efficiency and reduced coating stress. Hence, the metallic or ceramic coating has a lateral homogeneity within 2% and contaminants less than 5%, being optimal for laser ablation processing. With this method, a short (few ms) and well defined pulse of impurities with about 1017 particles can be injected close to the last closed flux surface of Wendelstein 7-X. In particular, a significant amount of atoms with a velocity of about 1 km/s enters the plasma within 1 ms. The atoms are followed by a negligible concentration of slower clusters and macro-particles. This qualifies the use of the targets and applied laser settings for impurity transport studies with the laser blow-off system in Wendelstein 7-X. © 2020 Author(s)

Efficacy of an Extracorporeal Endotoxin Adsorber System during Hyperdynamic Porcine Endotoxemia

Background: Endotoxemia is a crucial factor in the pathogenesis of sepsis. Elimination of endotoxin is aimed at the reduction of sepsis-related morbidity and lethality. The objective of this study was to examine the impact of an endotoxin adsorber on hemodynamics, O2 exchange and metabolism during resuscitated porcine endotoxemia. Methods: Twenty pigs were randomized into 2 intervention groups (n = 7 each) and 1 control group (n = 6). Endotoxemia was induced by continuous intravenous application of lipopolysaccharide for 8 h. Adsorber therapy was started at the same time as the induction of endotoxemia or 2 h later. An extracorporeal hemoperfusion device using immobilized human serum albumin for endotoxin adsorption was used. Results: Hemodynamic, metabolic and acid-base parameters, as well as the kinetics of interleukin (IL)-6, IL-8, IL-10 and tumor necrosis factor-α, were characteristic for endotoxic shock. Endotoxin plasma levels were low (arterial, hepatic and portal vein). None of the parameters were significantly influenced by the adsorber system. Conclusion: Despite typical clinical signs of endotoxemia, the adsorber system had no significant effect on hemodynamic, metabolic and acid-base parameters during endotoxic shock. The reasons for the absence of an effect are elusive; however, failure of the method per se or exceeded capacity of the adsorber cannot be excluded

Quantitative comparison of impurity transport in turbulence reduced and enhanced scenarios at Wendelstein 7-X

We assess the turbulent particle transport being responsible for the limitation of the confinement and, thus, the overall performance of the neoclassically optimized stellarator Wendelstein 7-X. The radial particle transport is experimentally inferred from the evaluation of impurity injection into turbulence reduced and enhanced plasma scenarios revealing a completely different confinement behavior. The impact of the density gradient on the turbulent ion transport is theoretically estimated using large-scale non-linear gyro-kinetic simulations enabling, for the first time in Wendelstein 7-X, a quantitative comparison to the experimentally assessed impurity transport properties. We demonstrate that impurity transport in most of the Wendelstein 7-X discharges, up to now impossible to cover only with neoclassical estimations, is dominated by turbulence and can be modelled via gyro-kinetic simulations