| 1. |
- Olofsson, K. Erik J., et al.
(författare)
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Cascade and multibatch subspace system identification for multivariate vacuum-plasma response characterisation
- 2011
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Ingår i: Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC11). ; , s. 2614-2619
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Konferensbidrag (refereegranskat)abstract
- A particular cascade structure system identification problem is formulated for the purpose of characterizing the vacuum-plasma response for a magnetic confinement fusion experiment. A predictor-form closed-loop subspace system identification approach is advocated due to (i) plant instability (ii) sizes of input-output vectors and (iii) inherent multivariate eigenmodes of the physical system. Since experiment data come in relatively short batches, specialised means for data merging for subspace identification are developed. A batchwise deletegroup jackknife procedure is utilised to estimate the standard error of the estimate of the dominant unstable empirical plasma response eigenvalue.
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| 2. |
- Olofsson, K. Erik J., et al.
(författare)
-
Closed-loop MIMO ARX estimation of concurrent external plasma response eigenmodes in magnetic confinement fusion
- 2010
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Ingår i: Proceedings of the 49th Conference on Decision and Control (CDC’10). ; , s. 2954-2959
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Konferensbidrag (refereegranskat)abstract
- Detailed experimental MIMO models of plasma stability behaviour are becoming increasingly important in magnetic confinement fusion (MCF) energy research as an assortment of magnetohydrodynamic (MHD) instabilities develop when fusion performance is pushed. Some of these problems could perhaps be handled by magnetic feedback. We here show a practical method for experimental closed-loop multi-input multi-output (MIMO) characterisation of the macroscopic stability of toroidal MCF devices. It is demonstrated, by application to the MCF experiment EXTRAP T2R, that MHD eigenmodes can be detected using the workhorse MIMO autoregressive exogeneous (ARX) model structure. Plausibly, the presented methodology could significantly improve highly-desired magnetic feedback accuracy in MCF.
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| 3. |
- Olofsson, K. Erik J., et al.
(författare)
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Predictor-based multivariable closed-loop system identification of the EXTRAP T2R reversed field pinch external plasma response
- 2011
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 53:8, s. 084003-
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Tidskriftsartikel (refereegranskat)abstract
- The usage of computationally feasible overparametrized and nonregularized system identification signal processing methods is assessed for automated determination of the full reversed-field pinch external plasma response spectrum for the experiment EXTRAP T2R. No assumptions on the geometry of eigenmodes are imposed. The attempted approach consists of high-order autoregressive exogenous estimation followed by Markov block coefficient construction and Hankel matrix singular value decomposition. It is seen that the obtained 'black-box' state-space models indeed can be compared with the commonplace ideal magnetohydrodynamics (MHD) resistive thin-shell model in cylindrical geometry. It is possible to directly map the most unstable autodetected empirical system pole to the corresponding theoretical resistive shell MHD eigenmode.
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| 4. |
- Olofsson, K. Erik J., et al.
(författare)
-
Vector dither experiment design and direct parametric identification of reversed-field pinch normal modes
- 2009
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 9781424438716 ; , s. 1348-1353
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Konferensbidrag (refereegranskat)abstract
- Magnetic confinement fusion (MCF) research ambitiously endeavours to develop a major future energy source. MCF power plant designs, typically some variation on the tokamak, unfortunately suffer from magnetohydrodynamic (MHD) instabilities. One unstable mode is known as the resistive-wall mode (RWM) which is a macroscopically global type of perturbation that can degrade or even terminate the plasma in the reactor if not stabilized. In this work the topic of RWMs is studied for the reversed-field pinch (RFP), another toroidal MCF concept, similar to the tokamak. The problem of identifying RWM dynamics during closed-loop operation is tackled by letting physics-based parametric modeling join forces with convex programming experiment design. An established MHD normal modes description is assessed for the RFP by synthesizing a multivariable dither signal where spatial fourier modes are spectrally shaped, with regard to real experiment constraints, to yield minimum variance parameter estimates in the prediction-error framework. The dithering is applied to the real RFP plant EXTRAP-T2R, and experimental MHD spectra are obtained by an automated procedure.
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