Active control of multiple resistive wall modes
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
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.
Electric coils; Feedback control; Growth (materials); Magnetohydrodynamics; Mathematical models; Plasmas
IdentifiersURN: urn:nbn:se:kth:diva-5428DOI: 10.1088/0741-3335/47/12B/S03ISI: 000234420700005ScopusID: 2-s2.0-27744525924OAI: oai:DiVA.org:kth-5428DiVA: diva2:9790
QC 201008262006-03-082006-03-082012-03-22Bibliographically approved