Simulation System for the Wendelstein 7-X Safety Control System

The Wendelstein 7-X (W7-X) Safety Instrumented System (SIS) ensures personal safety and investment protection. The development and implementation of the SIS are based on the international safety standard for the process industry sector, IEC 61511. The SIS exhibits a distributed and hierarchical organized architecture consisting of a central Safety System (cSS) on the top and many local Safety Systems (lSS) at the bottom. Each technical component or diagnostic system potentially hazardous for the staff or for the device is equipped with an lSS. The cSS is part of the central control system of W7-X. Whereas the lSSs are responsible for the safety of each individual component, the cSS ensures safety of the whole W7-X device. For every operation phase of the W7-X experiment hard- and software updates for the SIS are mandatory. New components with additional lSS functionality and additional safety signals have to be integrated. Already established safety functions must be adapted and new safety functions have to be integrated into the cSS. Finally, the safety programs of the central and local safety systems have to be verified for every development stage and validated against the safety requirement specification. This contribution focuses on the application of a model based simulation system for the whole SIS of W7-X. A brief introduction into the development process of the SIS and its technical realization will be give followed by a description of the design and implementation of the SIS simulation system using the framework SIMIT (Siemens). Finally, first application experiences of this simulation system for the preparation of the SIS for the upcoming operation phase OP 1.2b of W7-X will be discussed

Findif code simulations of OP-1.1 Wendelstein 7-X discharges

The current development state of the finite difference, multi-fluid, 3D plasma code Findif is detailed. The code was run on four meshes prepared for the OP-1.1 wall geometry of the Wendelstein 7-X stellarator. The meshes were produced for 4 magnetic configurations; two of them are finite-beta (non vacuum). The simulated volume covers plasma edge; the computations of limiter heat load distributions were the main goal. Plasma radiation was not taken into account.Докладно наведено поточну стадію розробки кінцево-різницевого тривимірного коду Findif для багаторідинної моделі плазми. Код було запущено на чотирьох сітках, підготовлених для геометрії стінки OP-1.1 стеларатора Wendelstein 7-X. Сітки згенеровано для 4-х магнітних конфігурацій, дві з яких – зі скінченним бета (не вакуум). Змодельований об’єм охоплює край плазми; основна мета полягає в розрахунках розподілів теплових навантажень на лімітер. Випромінювання плазми не враховувалося.Подробно изложена текущая стадия разработки конечно-разностного трехмерного кода Findif для многожидкостной модели плазмы. Код был запущен на четырех сетках, подготовленных для геометрии стенки OP-1.1 стелларатора Wendelstein 7-X. Сетки сгенерированы для 4-х магнитных конфигураций, две из которых – с конечным бета (не вакуум). Смоделированный объем охватывает край плазмы; основная цель заключается в расчетах распределений тепловых нагрузок на лимитер. Излучение плазмы не учитывалось

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)

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

Physics-regularized neural network of the ideal-MHD solution operator in Wendelstein 7-X configurations

The stellarator is a promising concept to produce energy from nuclear fusion by magnetically confining a high-pressure plasma. In a stellarator, the confining field is three-dimensional, and the computational cost of solving the 3D MHD equations currently limits stellarator research and design. Although data-driven approaches have been proposed to provide fast 3D MHD equilibria, the accuracy with which equilibrium properties are reconstructed is unknown. In this work, we describe an artificial neural network (NN) that quickly approximates the ideal-MHD solution operator in Wendelstein 7-X (W7-X) configurations. This model fulfils equilibrium symmetries by construction. The MHD force residual regularizes the solution of the NN to satisfy the ideal-MHD equations. The model predicts the equilibrium solution with high accuracy, and it faithfully reconstructs global equilibrium quantities and proxy functions used in stellarator optimization. The regularization term enforces that the NN reduces the ideal-MHD force residual, and solutions that are better than ground truth equilibria can be obtained at inference time. We also optimize W7-X magnetic configurations, where desiderable configurations can be found in terms of fast particle confinement. This work demonstrates with which accuracy NN models can approximate the 3D ideal-MHD solution operator and reconstruct equilibrium properties of interest, and it suggests how they might be used to optimize stellarator magnetic configurations.Comment: 46 pages, 23 figures, to be submitted to Nuclear Fusio

Gyro orbit simulations of neutral beam injection in Wendelstein 7-X

Simulations exploring neutral beam operation in Wendelstein 7-X (W7-X) at reduced magnetic field are performed using a newly implemented gyro orbit model in the BEAMS3D code. Operation at field strengths below the nominal 2.5 T are seen as a path to explore both high beta plasmas and as a means to access magnetic configurations not possible at 2.5 T. As the field strength becomes smaller, the gyro radius for 55 keV fast protons grows from ${\sim}1\,\mathrm{cm}$ at 2.5 T to ${\sim}5\,\mathrm{cm}$ at 0.75 T in a device with minor radius ${\sim}50\,\mathrm{cm}$ bringing into question the applicability of the gyro center approximation. To address this a gyro orbit model was implemented in the BEAMS3D code. Agreement is found between the gyro center and gyro orbit models in a circular cross section tokamak equilibrium at high field. A set of W7-X equilibria are assessed with fixed density and temperature profiles but decreasing magnetic field strength (increasing plasma beta). Neutral beam deposition is found to be mostly unaffected with changes in the core of the plasma associated with the Shafranov-shift. In general good agreement is found between gyro orbit and gyro center simulations at 2.5 T. Both models indicate increasing losses with decreasing magnetic field strength with the gyro orbit losses being higher at all field strengths. Gyro orbit simulations to the first wall of W7-X show a change in loss pattern with decreasing magnetic field strength. A preliminary assessment of losses to fast ion loss detectors are made