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Active control of multiple resistive wall modes
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
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.
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.
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2005 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, no 12 B, B25-B36 p.Article in journal (Refereed) Published
Abstract [en]

 A two-dimensional array of saddle coils at M-c poloidal and N-c toroidal positions is used on the EXTRAP T2R reversed-field pinch (Brunsell P R et al 2001 Plasma Phys. Control. Fusion 43 1457) to study active control of resistive wall modes (RWMs). Spontaneous growth of several RWMs with poloidal mode number m = 1 and different toroidal mode number n is observed experimentally, in agreement with linear MHD modelling. The measured plasma response to a controlled coil field and the plasma response computed using the linear circular cylinder MHD model are in quantitive agreement. Feedback control introduces a linear coupling of modes with toroidal mode numbers n, n' that fulfil the condition vertical bar n - n'vertical bar = N-c. Pairs of coupled unstable RWMs are present in feedback experiments with an array of Mc x Nc = 4 x 16 coils. Using intelligent shell feedback, the coupled modes are generally not controlled even though the field is suppressed at the active coils. A better suppression of coupled modes may be achieved in the case of rotating modes by using the mode control feedback scheme with individually set complex gains. In feedback with a larger array of Mc x Nc = 4 x 32 coils, the coupling effect largely disappears, and with this array, the main internal RWMs n = -11, -10, +5, +6 are all simultaneously suppressed throughout the discharge (7-8 wall times). With feedback there is a two-fold extension of the pulse length, compared to discharges without feedback.

Place, publisher, year, edition, pages
2005. Vol. 47, no 12 B, B25-B36 p.
Keyword [en]
Electric coils; Feedback control; Growth (materials); Magnetohydrodynamics; Mathematical models; Plasmas
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5428DOI: 10.1088/0741-3335/47/12B/S03ISI: 000234420700005Scopus ID: 2-s2.0-27744525924OAI: oai:DiVA.org:kth-5428DiVA: diva2:9790
Note
QC 20100826Available 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
2. Visible spectroscopy as a sensitive diagnostic tool for fusion plasmas
Open this publication in new window or tab >>Visible spectroscopy as a sensitive diagnostic tool for fusion plasmas
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

To further the understanding and knowledge about fusion plasmas and their behaviour during different conditions, it is important to be able to collect information about the plasma and the processes occurring within it. Visible spectroscopy, or the study of the visible wavelength light emitted by the plasma, is a useful tool in this search for knowledge.

This thesis is based on experiments where visible wavelength light has been measured and analysed in order to determine quantities about the emitting source. Doppler shift measurements of spectral lines have been utilised to determine the toroidal rotation velocities of plasma impurity ions and to study the correlation with mode rotation and the effect of active feedback control of the resistive wall modes. Information on the impurities present in the plasma has been determined and the calibrated intensities of spectral lines has yielded impurity concentrations, particle fluxes and electron temperature and densities. Ion temperatures have been determined from Doppler broadening measurements.

The measured vibrational and rotational band structure of deuterium molecular spectra has been analysed in order to calculate rotational and vibrational temperatures, relative populations and molecular particle fluxes. The effect of the molecular flux on simple calculations of atomic flux has also been studied. Specific molecular states and transitions of deuterium have also been probed with synchrotron radiation to study the level and transition energies.

The measurement and analysis of visible wavelength light has been demonstrated to be a sensitive diagnostic tool in the quest for increased knowledge about fusion plasmas and molecular structure.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 29 p.
Series
Trita-FYS, ISSN 0280-316X ; 2005:64
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-572 (URN)91-7178-222-2 (ISBN)
Presentation
2005-12-06, Sal FA31, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20101215Available from: 2005-12-23 Created: 2005-12-23 Last updated: 2010-12-15Bibliographically approved

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Publisher's full textScopushttp://www.iop.org/EJ/abstract/0741-3335/47/12B/S03

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Brunsell, PerRachlew, Elisabeth

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