81 research outputs found
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
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
Nonlinear gyrokinetic PIC simulations in stellarators with the code EUTERPE
In this work, the first nonlinear particle-in-cell simulations carried out in
a stellarator with the global gyrokinetic code EUTERPE using realistic plasma
parameters are reported. Several studies are conducted with the aim of enabling
reliable nonlinear simulations in stellarators with this code. First, EUTERPE
is benchmarked against ORB5 in both linear and nonlinear settings in a tokamak
configuration. Next, the use of noise control and stabilization tools, a
Krook-type collision operator, markers weight smoothing and heating sources is
investigated. It is studied in detail how these tools influence the linear
growth rate of instabilities in both tokamak and stellarator geometries and
their influence on the linear zonal flow evolution in a stellarator. Then, it
is studied how these tools allow improving the quality of the results in a set
of nonlinear simulations of electrostatic turbulence in a stellarator
configuration.
Finally, these tools are applied to a W7-X magnetic configuration using
experimental plasma parameters.Comment: 24 pages, 19 figure
Fast simulations for large aspect ratio stellarators with the neoclassical code KNOSOS
In this work, a new version of KNOSOS is presented. KNOSOS is a
low-collisionality radially-local, bounce-averaged neoclassical code that is
extremely fast, and at the same time, includes physical effects often neglected
by more standard codes: the component of the magnetic drift that is tangent to
the flux-surface and the variation of the electrostatic potential on the
flux-surface. An earlier version of the code could only describe configurations
that were sufficiently optimized with respect to neoclassical transport. KNOSOS
can now be applied to any large aspect ratio stellarator, and its performance
is demonstrated by means of detailed simulations in the configuration space of
Wendelstein 7-X.Comment: IAEA paper, submitted to Nuclear Fusio
Deposition of 13C tracer and impurity elements on the divertor of Wendelstein 7-X
Carbon impurity transport and deposition were investigated in the Wendelstein 7-X stellarator by injecting isotopically labelled methane ((CH4)-C-13) into the edge plasma during the last plasma operations of its Operational Phase (OP) 1.2B experimental campaign. C-13 deposition was measured by secondary ion mass spectrometry (SIMS) on three upper divertor tiles located on the opposite side of the vessel to the(13)CH(4) inlet. The highest C-13 inventories were found as stripe-like patterns on both sides of the different strike lines. These high deposition areas were also analysed for their impurity contents and the depth profiles of the main elements in the layers. Layered deposition of different impurity elements such as Cr, Ni, Mo and B was found to reflect various events such as high metallic impurities during the OP1.2A and three boronizations carried out during OP1.2B.Peer reviewe
Accelerated Bayesian inference of plasma profiles with self-consistent MHD equilibria at W7-X via neural networks
High- operations require a fast and robust inference
of plasma parameters with a self-consistent MHD equilibrium. Precalculated MHD
equilibria are usually employed at W7-X due to the high computational cost. To
address this, we couple a physics-regularized NN model that approximates the
ideal-MHD equilibrium with the Bayesian modeling framework Minerva. We show the
fast and robust inference of plasma profiles (electron temperature and density)
with a self-consistent MHD equilibrium approximated by the NN model. We
investigate the robustness of the inference across diverse synthetic W7-X
plasma scenarios. The inferred plasma parameters and their uncertainties are
compatible with the parameters inferred using the VMEC, and the inference time
is reduced by more than two orders of magnitude. This work suggests that MHD
self-consistent inferences of plasma parameters can be performed between shots.Comment: 18 pages, 6 figure
Impurity transport study based on measurement of visible wavelength high-n charge exchange transitions at W7-X
A recently installed high-speed charge exchange diagnostic at the W7-X stellarator has been used to identify several high-n Rydberg emission lines near 500 nm following impurity injections. The wavelengths of observed high-n Rydberg transitions are independent of the impurity species and originate from ions with ionization states ranging from 14+ to 45+ suggesting that this approach can be applied to a variety of heavy impurities. Moreover, little to no passive signal is observed since the high-n energy levels are unlikely to be populated by electron impact excitation. The combination of the newly developed diagnostic and the observation of high-n Rydberg states provides spatially resolved, high-speed measurements of multiple charge states which are analyzed in a Bayesian inference framework to determine both impurity diffusion and convection profiles. Measurements from the 2023 experimental campaign conclusively show high diffusion and an inward pinch in the core, well above predictions by neoclassical theory
On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas
The formation of the radial electric field, E-r in the scrape-off layer (SOL) has been experimentally studied for attached divertor conditions in stellarator W7-X. The main objective of this study is to test the validity in a complex three-dimensional (3D) island divertor of simple models, typically developed in tokamaks, relating E-r in the SOL to the sheath potential drop gradient at the target. Additionally, we investigate the effect of the edge E-r shear on the reduction of density fluctuation amplitude, a well-established phenomenon according to the existing bibliography. The main diagnostic for measurements in the SOL is a V-band Doppler reflectometer that can provide the measurement of the E-r and density fluctuations with good spatial resolution. 3D measurements of divertor parameters have been carried out using infrared cameras, with the exponential decay length of the divertor heat flux (lambda(q)) resulting in a suitable proxy for the model-relevant lambda(T), the exponential decay length of the temperature at the divertor. In the investigated attached regimes, it is shown for the first time that the formation of the E-r in the SOL depends on parameters at the divertor, following a E-r proportional to T-e/lambda(q) qualitatively similar to that found in a tokamak. Then, from the analyzed plasmas, the observed E-r shear at the edge is linked to a moderate local reduction of the amplitude of density fluctuations
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