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Advanced feedback control methods in EXTRAP T2R
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0002-5259-0458
2006 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 7, 072109- p.Article in journal (Refereed) Published
Abstract [en]

Previous experiments in the EXTRAP T2R reversed field pinch device have shown the possibility of suppression of multiple resistive wall modes (RWM). A feedback system has been installed in EXTRAP T2R having 100% coverage of the toroidal surface by the active coil array. Predictions based on theory and the previous experimental results show that the number of active coils should be sufficient for independent stabilization of all unstable RWMs in the EXTRAP T2R. Experiments using different feedback schemes are performed, comparing the intelligent shell, the fake rotating shell, and the mode control with complex feedback gains. Stabilization of all unstable RWMs throughout the discharge duration of t(d)approximate to 10 tau(w) is seen using the intelligent shell feedback scheme. Mode rotation and the control of selected Fourier harmonics is obtained simultaneously using the mode control scheme with complex gains. Different sensor signals are studied. A feedback system with toroidal magnetic field sensors could have an advantage of lower feedback gain needed for the RWM suppression compared to the system with radial magnetic field sensors. In this study, RWM suppression is demonstrated, using also the toroidal field component as a sensor signal in the feedback system.

Place, publisher, year, edition, pages
2006. Vol. 13, no 7, 072109- p.
Keyword [en]
Electric discharges; Feedback control; Magnetic fields; Sensors; Stabilization; Surface properties
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5430DOI: 10.1063/1.2241980ISI: 000239424400010Scopus ID: 2-s2.0-33746926012OAI: oai:DiVA.org:kth-5430DiVA: diva2:9792
Note
QC 20100826. Ändrat från submitted till published (20100826)Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Resistive Wall Mode Stability and Control in the Reversed Field Pinch
Open this publication in new window or tab >>Resistive Wall Mode Stability and Control in the Reversed Field Pinch
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Control of MHD instabilities using a conducting wall together with external magnetic fields is an important route to improved performance and reliability in fusion devices. Active control of MHD modes is of interest for both the Advanced Tokamak and the Reversed Field Pinch (RFP) configurations. A wide range of unstable, current driven MHD modes is present in the RFP. An ideally conducting wall facing the plasma can in principle provide stabilization to these modes. However, a real, resistive wall characterized by a wall field diffusion time, cannot stabilize the ideal MHD modes unless they rotate with Alfvénic velocity, which is usually not the case. With a resistive wall, the ideal modes are converted into resistive wall modes (RWM) with growth rates comparable to the inverse wall time. Resistive wall modes have been studied in the EXTRAP T2R thin shell RFP device. Growth rates have been measured and found in agreement with linear MHD stability calculations. An advanced system for active control has been developed and installed on the EXTRAP T2R device. The system includes an array of 128 active saddle coils, fully covering the torus surface. Experiments on EXTRAP T2R have for the first time demonstrated simultaneous active suppression of multiple independent RWMs. In experiments with a partial array, coupling of different modes due to the limited number of feedback coils has been observed, in agreement with theory. Different feedback strategies, such as the intelligent shell, the rotating shell, and mode control have been studied. Further, feedback operation with different types of magnetic field sensors, measuring either the radial or the toroidal field components have been compared

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. viii, 46 p.
Series
Trita-EE, ISSN 1653-5146 ; 2006:005
Keyword
Resistive wall modes, RWM, active control, feedback, MHD modes, Reversed-Field pinch, RFP, intelligent shell, mode control
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-3867 (URN)91-7178-285-0 (ISBN)
Public defence
2006-03-17, H1, Teknikringen 33, Stockholm, 10:30
Opponent
Supervisors
Note
QC 20100929Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2010-09-29Bibliographically approved

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Brunsell, Per

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