543 research outputs found
New applications of Equinox code for real-time plasma equilibrium and profile reconstruction for tokamaks
Recent development of real-time equilibrium code Equinox [1] using a
fixed-point algorithm [2] allow major plasma magnetic parameters to be
identified in real-time, using rigorous analytical method. The code relies on
the boundary flux code providing flux values on the first wall of vacuum
vessel. By means of least-square minimization of differences between magnetic
field obtained from previous solution and the next measurements the code
identifies the source term of the non-linear Grad-Shafranov equation [3]. The
strict use of analytical equations together with a flexible algorithm offers an
opportunity to include new measurements into stable magnetic equilibrium code
and compare the results directly between several tokamaks while maintaining the
same physical model (i.e. no iron model is necessary inside the equilibrium
code). The successful implementation of this equilibrium code for JET and Tore
Supra have been already published [1], in this paper, we show the preliminary
results of predictive runs of the Equinox code using the ITER geometry.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Reconstruction of the equilibrium of the plasma in a Tokamak and identification of the current density profile in real time
The reconstruction of the equilibrium of a plasma in a Tokamak is a free
boundary problem described by the Grad-Shafranov equation in axisymmetric
configuration. The right-hand side of this equation is a nonlinear source,
which represents the toroidal component of the plasma current density. This
paper deals with the identification of this nonlinearity source from
experimental measurements in real time. The proposed method is based on a fixed
point algorithm, a finite element resolution, a reduced basis method and a
least-square optimization formulation. This is implemented in a software called
Equinox with which several numerical experiments are conducted to explore the
identification problem. It is shown that the identification of the profile of
the averaged current density and of the safety factor as a function of the
poloidal flux is very robust
A nudging-based data assimilation method: the Back and Forth Nudging (BFN) algorithm
International audienceThis paper deals with a new data assimilation algorithm, called Back and Forth Nudging. The standard nudging technique consists in adding to the equations of the model a relaxation term that is supposed to force the observations to the model. The BFN algorithm consists in repeatedly performing forward and backward integrations of the model with relaxation (or nudging) terms, using opposite signs in the direct and inverse integrations, so as to make the backward evolution numerically stable. This algorithm has first been tested on the standard Lorenz model with discrete observations (perfect or noisy) and compared with the variational assimilation method. The same type of study has then been performed on the viscous Burgers equation, comparing again with the variational method and focusing on the time evolution of the reconstruction error, i.e. the difference between the reference trajectory and the identified one over a time period composed of an assimilation period followed by a prediction period. The possible use of the BFN algorithm as an initialization for the variational method has also been investigated. Finally the algorithm has been tested on a layered quasi-geostrophic model with sea-surface height observations. The behaviours of the two algorithms have been compared in the presence of perfect or noisy observations, and also for imperfect models. This has allowed us to reach a conclusion concerning the relative performances of the two algorithms
A new method for data assimilation: the back and forth nudging algorithm
International audienceIn this paper, we propose an improvement to the Back and Forth Nudging algorithm for handling diffusion in the context of geophysical data assimilation. We detail the Diffusive Back and Forth Nudging algorithm, in which the sign of the diffusion term is changed in the backward integrations. We study the convergence of this algorithm, in particular for linear transport equations
An easy-to-implement and efficient data assimilation method for the identification of the initial condition: the Back and Forth Nudging (BFN) algorithm
International audienceThis paper deals with a new data assimilation algorithm called the Back and Forth Nudging. The standard nudging technique consists in adding to the model equations a relaxation term, which is supposed to force the model to the observations. The BFN algorithm consists of repeating forward and backward resolutions of the model with relaxation (or nudging) terms, that have opposite signs in the direct and inverse resolutions, so as to make the backward evolution numerically stable. We then applied the Back and Forth Nudging algorithm to a simple non-linear model: the 1D viscous Burgers' equations. The tests were carried out through several cases relative to the precision and density of the observations. These simulations were then compared with both the variational assimilation (VAR) and quasi-inverse (QIL) algorithms. The comparisons deal with the programming, the convergence, and time computing for each of these three algorithms
A new method for data assimilation: the back and forth nudging algorithm
International audienceIn this paper, we propose an improvement to the Back and Forth Nudging algorithm for handling diffusion in the context of geophysical data assimilation. We detail the Diffusive Back and Forth Nudging algorithm, in which the sign of the diffusion term is changed in the backward integrations. We study the convergence of this algorithm, in particular for linear transport equations
Real-Time Equilibrium Reconstruction in a Tokamak
This paper deals with the numerical reconstruction of the plasma current
density in a Tokamak and of its equilibrium. The problem consists in the
identification of a non-linear source in the 2D Grad-Shafranov equation, which
governs the axisymmetric equilibrium of a plasma in a Tokamak. The experimental
measurements that enable this identification are the magnetics on the vacuum
vessel, but also polarimetric and interferometric measures on several chords,
as well as motional Stark effect or pressure measurements. The reconstruction
can be obtained in real-time using a finite element method, a non-linear
fixed-point algorithm and a least-square optimization procedure
EQUILIBRIUM RECONSTRUCTION FROM DISCRETE MAGNETIC MEASUREMENTS IN A TOKAMAK
International audienceWe describe an algorithm for the reconstruction of the equilibrium in a Tokamak from discrete magnetic measurements. In order to solve this inverse problem we first use toroidal harmonics to compute Cauchy boundary conditions on a fixed closed contour. Then we use these Cauchy boundary conditions to solve a non-linear source identification problem
- …