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- Frassinetti, Lorenzo, et al.
(author)
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A method for the estimate of the wall diffusion for non-axisymmetric fields using rotating external fields
- 2013
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 55:8, s. 084001-
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Journal article (peer-reviewed)abstract
- A new method for the estimate of the wall diffusion time of non-axisymmetric fields is developed. The method based on rotating external fields and on the measurement of the wall frequency response is developed and tested in EXTRAP T2R. The method allows the experimental estimate of the wall diffusion time for each Fourier harmonic and the estimate of the wall diffusion toroidal asymmetries. The method intrinsically considers the effects of three-dimensional structures and of the shell gaps. Far from the gaps, experimental results are in good agreement with the diffusion time estimated with a simple cylindrical model that assumes a homogeneous wall. The method is also applied with non-standard configurations of the coil array, in order to mimic tokamak-relevant settings with a partial wall coverage and active coils of large toroidal extent. The comparison with the full coverage results shows good agreement if the effects of the relevant sidebands are considered.
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| 4. |
- Frassinetti, Lorenzo, et al.
(author)
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A Technique for the Estimation of the Wall Diffusion Time
- 2012
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In: 54th Meeting of the APS Division of Plasma Physics, November 2012, Providence, USA.
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Conference paper (peer-reviewed)abstract
- Feedback systems are important tools for an advanced control of the MHD instabilities in fusion plasmas, both for the suppression of undesired modes, such as RWMs, and for the generation of external perturbations for ELM suppression. A good knowledge of the diffusion time through the machine wall of each external harmonics is necessary for reaching optimal performances of the feedback algorithms.A correct theoretical estimation is not easy due the presence of three-dimensional mechanical structures in the devices, such as shell cuts and external conductive structures that need to be considered. Identification of differences in the vertical and horizontal diffusion time are not simple from a theoretical point of view.This work will present a relatively simple technique to experimentally estimate the diffusion time for each harmonic. The technique is based on the generation of rotating external magnetic perturbations in vacuum and on the quantification of the wall screening from the measured field inside the wall. The technique will be able to quantify possible differences among the horizontal and vertical diffusion time. In the final part of the work, the comparison with the results obtained with a closed-loop identification algorithm of the machine plant will be discussed.
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| 7. |
- Setiadi, Agung Chris, et al.
(author)
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Design and operation of fast model predictive controller for stabilization of magnetohydrodynamic modes in a fusion device
- 2016
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In: Proceedings of the IEEE Conference on Decision and Control. - : IEEE conference proceedings. - 9781479978861 ; , s. 7347-7352
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Conference paper (peer-reviewed)abstract
- Magnetic confinement fusion (MCF) devices suffer from magnetohydrodynamic (MHD) instabilities. A particular unstable mode, known as the resistive wall mode (RWM), is treated in this work. The RWM perturbs the plasma globally and can degrade the confinement or even terminate the plasma if not stabilized. This paper presents a control design approach to stabilize the RWM in the reversed-field pinch (RFP). The approach consists of: closed-loop system identification of the RFP, design of a fast model predictive controller and experimental validation of the controller. Experimental results shows that the proposed controller manages to stabilize the RWM in plasma.
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| 8. |
- Setiadi, Agung Chris, 1986-, et al.
(author)
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Graybox Modelling of EXTRAP T2R with Vacuum-Plasma Separation and Optimal Control Design of Resistive Wall Modes
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Journal article (peer-reviewed)abstract
- This paper presents a graybox methodology to model the Resistive Wall Mode instability by combining first principle approach and system identification technique. In particular we propose a separate vacuum and plasma modeling with cascade interconnection. The shell is modeled using CARIDDI code which solves the 3D integral formulation of eddy current problem, whereas the plasma response is obtained empirically by system identification. Furthermore the resulting model is used to design an optimal feedback control. The model and feedback control is validated experimentally in EXTRAP T2R reversed-field pinch, where RWMs stabilization and non-axisymmetric mode sustainment is considered.
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| 9. |
- Setiadi, Agung Chris, et al.
(author)
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Implementation of model predictive control for resistive wall mode stabilization on EXTRAP T2R
- 2015
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In: Plasma Physics and Controlled Fusion. - : Institute of Physics Publishing (IOPP). - 0741-3335 .- 1361-6587. ; 57:10
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Journal article (peer-reviewed)abstract
- A model predictive control (MPC) method for stabilization of the resistive wall mode (RWM) in the EXTRAP T2R reversed-field pinch is presented. The system identification technique is used to obtain a linearized empirical model of EXTRAP T2R. MPC employs the model for prediction and computes optimal control inputs that satisfy performance criterion. The use of a linearized form of the model allows for compact formulation of MPC, implemented on a millisecond timescale, that can be used for real-time control. The design allows the user to arbitrarily suppress any selected Fourier mode. The experimental results from EXTRAP T2R show that the designed and implemented MPC successfully stabilizes the RWM.
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| 10. |
- Setiadi, Agung Chris, 1986-, et al.
(author)
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Improved model predictive control of resistive wall modes by error field estimator in EXTRAP T2R
- 2016
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In: Plasma Physics and Controlled Fusion. - : Institute of Physics (IOP). - 0741-3335 .- 1361-6587. ; 58:12
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Journal article (peer-reviewed)abstract
- Many implementations of a model-based approach for toroidal plasma have shown better control performance compared to the conventional type of feedback controller. One prerequisite of model-based control is the availability of a control oriented model. This model can be obtained empirically through a systematic procedure called system identification. Such a model is used in this work to design a model predictive controller to stabilize multiple resistive wall modes in EXTRAP T2R reversed-field pinch. Model predictive control is an advanced control method that can optimize the future behaviour of a system. Furthermore, this paper will discuss an additional use of the empirical model which is to estimate the error field in EXTRAP T2R. Two potential methods are discussed that can estimate the error field. The error field estimator is then combined with the model predictive control and yields better radial magnetic field suppression.
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