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Reduced Order Modelling of Resistive Wall Modes in EXTRAP T2R Reversed-Field Pinch
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
DIEI, Università di Cassino e del Lazio Meridionale, Italy.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0002-5259-0458
DIEI, Università di Cassino e del Lazio Meridionale, Italy.
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2016 (English)In: 43rd European Physical Society Conference on Plasma Physics, EPS 2016, European Physical Society , 2016Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, we study the Resistive Wall Mode (RWM) instability in the EXTRAP T2R Reversed-Field Pinch. The RWM is a kink-like instability that grows in the time scale of magnetic field diffusion time through the conducting structures. The RWMs are highly affected by the complex three-dimensional conducting structures surrounding the plasma. The first part of the paper will describe the RWM modelling process in EXTRAP T2R using the CarMa computational tool. The code can rigorously take into account the complex geometry of the conducting structures in the solution of the plasma stability problem. The resulting model can be cast into a state space form, with the number of state variables up to several thousands. In the time scale of magnetic field diffusion time, it is possible to stabilize the RWMs by using feedback-controlled external magnetic perturbation to counteract the growing magnetic field caused by the RWMs. Hence, the final suppression level of the RWM is highly dependent on the features of the feedback controller; thus its careful design is needed. Advanced feedback control design method requires an accurate model and the CarMa computational tool can be used in this respect. However, handling such a complex model may pose severe problems both in the design phase and when implemented in real-time due to the computational load. Several model reduction techniques will be employed to address this issue, with the aim of getting to a simpler approximation of RWM response without neglecting the crucial physics information

Place, publisher, year, edition, pages
European Physical Society , 2016.
Keywords [en]
Reduced order model, reversed-field pinch, magnetohydrodynamic
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-200826Scopus ID: 2-s2.0-85013927660OAI: oai:DiVA.org:kth-200826DiVA, id: diva2:1070897
Conference
43rd European Physical Society Conference on Plasma Physics, EPS 2016, KU Leuven, Leuven, Belgium, 4 July 2016 through 8 July 2016
Note

QC 20170203

Available from: 2017-02-02 Created: 2017-02-02 Last updated: 2018-03-06Bibliographically approved
In thesis
1. Model based approach to resistive wall magnetohydrodynamic instability control: Experimental modeling and optimal control for the reversed-field pinch
Open this publication in new window or tab >>Model based approach to resistive wall magnetohydrodynamic instability control: Experimental modeling and optimal control for the reversed-field pinch
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The primary objective of fusion research is to realize a thermonuclear fusion power plant. The main method to confine the hot plasma is by using a magnetic field. The reversed-field pinch is a type of magnetic confinement device which suffers from variety of magnetohy- drodynamic (MHD) instabilities. A particular unstable mode that is treated in this work is the resistive wall mode (RWM), which occurs due to the current gradient in the RFP and has growth rates of the order of the magnetic diffusion time of the wall. Application of control engineering tools appears to allow a robust and stable RFP operation.A model-based approach to stabilize the RWMs is pursued in this thesis. The approach consists of empirical modeling of RWMs using a class of subspace identification methodology. The obtained model is then used as a basis for a model based controller. In particular the first experimental results of using a predictive control for RWM stabilization are obtained. It is shown that the formulation of the model based controller allows the user to incorporate several physics relevant phenomena along with the stabilization of RWM. Another use of the model is shown to estimate and compensate the inherent error field. The results are encouraging, and the methods appear to be generically useful as research tools in controlled magnetic confinement fusion.

Abstract [sv]

Fusionsforskningens primära mål är att förverkliga en ny typ av kraftverk baserade på termonukleär fusion. Den viktigaste metoden för att innesluta det heta plasmat är användandet av  magnetfält. ”Reverserat-fält pinch” (RFP) är en typ av anläggning för magnetisk inneslutning av fusionsplasma som uppvisar ett flertal magneto-hydrodynamiska instabiliteter. En specifik instabil mod som behandlas i detta arbete är”resistiv-vägg” moden (RWM). Den orsakas av strömgradienten i RFPn och tillväxer med en tidskonstant som är av samma storleksordning som magnetfältets diffusionstid i det omgivande metallskalet.  Tillämpning av verktyg från reglerteknikområdet förefaller tillåta en robust och stabil RFP drift. I detta arbete används ett modell-baserat tillvägagångssätt för kompensering av RWM. Det innefattar empirisk modellering av RWM med användning av ”subspace” system-identifieringsmetoder. Den erhållna modellen används sedan som grund för en modell-baserad regulator. De första experimentella resultaten från modell-prediktiv kompensering av RWM har erhållits.  I detta arbete har också visats att formuleringen av den modellbaserade regulatorn tillåter användaren att integrera flera relevanta fysikaliska aspekter förutom RWM. Ytterligare en användning av modellen är för att göra uppskattning och kompensering av avvikelser i anläggningens magnetfält, så kallade fält-fel. Resultaten är uppmuntrande, och det förefaller som om de undersökta metoderna är allmänt användbara som verktyg för forskning om magnetisk inneslutning av fusionsplasma.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. p. 59
Series
TRITA-EE, ISSN 1653-5146 ; 2016:192
Keywords
magnetohydrodynamic, model based control, reversed-field pinch
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-200817 (URN)978-91-7729-228-9 (ISBN)
Public defence
2017-02-09, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Supervisors
Note

QC 20170202

Available from: 2017-02-02 Created: 2017-02-02 Last updated: 2017-02-02Bibliographically approved

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Scopushttp://ocs.ciemat.es/EPS2016PAP/pdf/P2.047.pdf

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Brunsell, PerFrassinetti, Lorenzo

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