1,188 research outputs found
Combined distributed parameters and source estimation in tokamak plasma heat transport
International audienceWe investigate the joint estimation of time and space distributed parameters and input in the tokamak heat transport equation. This physical phenomenon can be modelled by a non-homogeneous linear parabolic partial differential equation (PDE). The analysis of this PDE is achieved in a finite dimensional framework using the cubic b-splines finite element method. The application of the parameter projection method results in a linear time-varying state-space model with unknown parameters and inputs. The DAISYS method proves the structural identifiability of the model and the EKF-UI-WDF estimates simultaneously the states, parameters and inputs. This methodology is applied on the tokamak plasma heat transport equation in order to reconstruct simultaneously its coefficients and its source term. Computer simulations on both mock-up and real data show the performance of the proposed technique
Adaptive Distributed Parameter and Input Estimation in Plasma Tokamak Heat Transport
International audienceIn this paper, the adaptive estimation of spatially varying diffusion and source term coefficients for a linear parabolic partial differential equation describing tokamak plasma heat transport is considered. An estimator is defined in the infinite-dimensional framework having the system state and the parameters' estimate as its states. Our scheme allows to estimate constant, spatially distributed and spatio-temporally distributed parameters as well as input with known upper bounds in time. While the parameters convergence depends on the plant signal richness assumption, the state convergence is established using the Lyapunov approach. Since the estimator is infinite-dimensional, the Galerkin finite-dimensional technique is used to implement it. In silico simulations are provided to illustrate the performance of the proposed approach
Adaptive Distributed Parameter and Input Estimation in Plasma Tokamak Heat Transport
International audienceIn this paper, the adaptive estimation of spatially varying diffusion and source term coefficients for a linear parabolic partial differential equation describing tokamak plasma heat transport is considered. An estimator is defined in the infinite-dimensional framework having the system state and the parameters' estimate as its states. Our scheme allows to estimate constant, spatially distributed and spatio-temporally distributed parameters as well as input with known upper bounds in time. While the parameters convergence depends on the plant signal richness assumption, the state convergence is established using the Lyapunov approach. Since the estimator is infinite-dimensional, the Galerkin finite-dimensional technique is used to implement it. In silico simulations are provided to illustrate the performance of the proposed approach
Gaussian process tomography for soft x-ray spectroscopy at WEST without equilibrium information
International audienceGaussian process tomography (GPT) is a recently developed tomography method based on the Bayesian probability theory [J. Svensson, JET Internal Report EFDA-JET-PR(11)24, 2011 and Li et al., Rev. Sci. Instrum. 84, 083506 (2013)]. By modeling the soft X-ray (SXR) emissivity field in a poloidal cross section as a Gaussian process, the Bayesian SXR tomography can be carried out in a robust and extremely fast way. Owing to the short execution time of the algorithm, GPT is an important candidate for providing real-time reconstructions with a view to impurity transport and fast magnetohydrodynamic control. In addition, the Bayesian formalism allows quantifying uncertainty on the inferred parameters. In this paper, the GPT technique is validated using a synthetic data set expected from the WEST tokamak, and the results are shown of its application to the reconstruction of SXR emissivity profiles measured on Tore Supra. The method is compared with the standard algorithm based on minimization of the Fisher information
Adaptive Space-Time Distributed Parameter and Input Estimation in Heat Transport with Unknown Bounds
International audienceIn this paper, we discuss on-line adaptive estimation of distributed diffusion and source term coefficients for a non-homogeneous linear parabolic partial differential equation describing heat transport. An estimator is defined in the infinite-dimensional framework having the system state and the parameters' estimate as its states. Our scheme allows to estimate spatially distributed and space-time distributed parameters. While the parameters convergence depends on the plant signal richness assumption, the state convergence is established using the Lyapunov approach. Since the estimator is infinite- dimensional, the b-splines Galerkin finite element method is used to implement it. In silico simulations are provided to illustrate the performance of the proposed approach
Overview of the JET results in support to ITER
The 2014–2016 JET results are reviewed in the light of their significance for optimising
the ITER research plan for the active and non-active operation. More than 60 h of plasma
operation with ITER first wall materials successfully took place since its installation in
2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER
is supported by first principle modelling. ITER relevant disruption experiments and first
principle modelling are reported with a set of three disruption mitigation valves mimicking
the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given,
stressing the importance of the magnetic configurations and the recent measurements of
fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal
confinement provide new information to elucidate the importance of the first wall material on
the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at βN ~ 1.8 and n/nGW
~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated
on high performance experiments. Prospects for the coming D–T campaign and 14 MeV
neutron calibration strategy are reviewed.European Commission (EUROfusion 633053
ASCOT: solving the kinetic equation of minority particle species in tokamak plasmas
A comprehensive description of methods, suitable for solving the kinetic
equation for fast ions and impurity species in tokamak plasmas using Monte
Carlo approach, is presented. The described methods include Hamiltonian
orbit-following in particle and guiding center phase space, test particle or
guiding center solution of the kinetic equation applying stochastic
differential equations in the presence of Coulomb collisions, neoclassical
tearing modes and Alfv\'en eigenmodes as electromagnetic perturbations relevant
to fast ions, together with plasma flow and atomic reactions relevant to
impurity studies. Applying the methods, a complete reimplementation of the
well-established minority species code ASCOT is carried out as a response both
to the increase in computing power during the last twenty years and to the
weakly structured growth of the code, which has made implementation of
additional models impractical. Also, a benchmark between the previous code and
the reimplementation is accomplished, showing good agreement between the codes.Comment: 13 pages, 9 figures, submitted to Computer Physics Communication
Investigation of a Multiple-Timescale Turbulence-Transport Coupling Method in the Presence of Random Fluctuations
One route to improved predictive modeling of magnetically confined fusion
reactors is to couple transport solvers with direct numerical simulations (DNS)
of turbulence, rather than with surrogate models. An additional challenge
presented by coupling directly with DNS is that the inherent fluctuations in
the turbulence, which limit the convergence achievable in the transport solver.
In this article, we investigate the performance of one numerical coupling
method in the presence of turbulent fluctuations. To test a particular
numerical coupling method for the transport solver, we use an
autoregressive-moving-average model to efficiently generate stochastic
fluctuations with statistical properties resembling those of a gyrokinetic
simulation. These fluctuations are then added to a simple, solvable problem,
and we examine the behavior of the coupling method. We find that monitoring the
residual as a proxy for the error can be misleading. From a pragmatic point of
view, this study aids us in the full problem of transport coupled to DNS by
predicting the amount of averaging required to reduce the fluctuation error and
obtain a specific level of accuracy.Comment: 18 pages, 9 figure
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