Change search
Refine search result
1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Setiadi, Agung Chris
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Resistive Wall Mode Studies utilizing External Magnetic Perturbations2014In: Proceeding of the 25th IAEA Fusion Energy Conference, 2014, Paper EX/P4-20Conference paper (Other academic)
  • 2.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Setiadi, Agung Chris
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Resistive Wall Mode Studies utilizing External Magnetic PerturbationsManuscript (preprint) (Other academic)
  • 3.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Yadikin, D.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabethth
    KTH, School of Engineering Sciences (SCI), Physics.
    Resistive wall mode feedback control experiments in EXTRAP T2R2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, 544-547 p.Conference paper (Refereed)
    Abstract [en]

    Experiments in EXTRAP T2R on RWM stabilization using intelligent shell feedback with a P-controller showed that mode suppression improves with increasing gain up to the system stability limit. A PD-controller gives faster response and allows operation with higher gain. The PI-controller is useful for suppression of modes driven by external resonant field error. Best mode suppression was in the present study achieved with a PID-controller.

  • 4.
    Cecconello, Marco
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Khan, Muhammad Waqas Mehmood
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Resistive tearing modes dynamics with plasma control in a reversed field pinch2008In: 35th EPS Conference on Plasma Physics 2008, EPS 2008 - Europhysics Conference Abstracts: Volume 32, Issue 1, 2008, 429-432 p.Conference paper (Refereed)
  • 5.
    Drake, James Robert
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bolzonella, T.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Baruzzo, T. M.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Guo, S. C.
    Igochine, V.
    Liu, Y. Q.
    Marchiori, G.
    Paccagnella, R.
    Rubinacci, G.
    Soppelsa, A.
    Villone, F.
    Yadikin, D.
    Martin, P.
    Zohm, H.
    Reversed-Field Pinch Contributions to Resistive Wall Mode Physics and Control2008Conference paper (Refereed)
    Abstract [en]

    Optimal feedback control of resistive-wall modes (RWM) is of common interest for toroidal fusionconcepts that use conducting walls for stabilization of ideal MHD modes. From the RWM control point of view,the RFP situation is in many respects similar to the advanced tokamak situation in the presence of very lowplasma rotation, where the most effective stabilizing mechanism is the feedback action of a set of active coils.Results from EXTRAP T2R (Sweden) and RFX-mod (Italy) RFP experiments have shown that full feedbackcontrol of multiple RWMs is possible and their deleterious effects can be completely suppressed. However it isnow important to optimize the RWM control systems both for the RFP and tokamak configuration for futureimplementation. Important aspects of optimization are effective mode identification and tracking capability,avoidance of the harmful effects of sideband modes (aliasing) in the control spectrum, minimized powerrequirements and robust controller stability. The paper describes collaborative work carried out on the two RFPexperiments. Controller models based on the mode harmonic control concept and on a state-space multipleinputmultiple-output intelligent shell concept are studied. Progress in development of optimal control schemesare presented both through experimental studies and simulations.

  • 6.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Khan, Muhammad Waqas Mehmood
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Active feedback control of QSH in EXTRAP-T2R2008Conference paper (Refereed)
  • 7.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fridström, Rickard
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Setiadi, Agung Chris
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Drake, James
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A Technique for the Estimation of the Wall Diffusion Time2012In: 54th Meeting of the APS Division of Plasma Physics, November 2012,  Providence, USA, 2012Conference paper (Refereed)
    Abstract [en]

    Feedback systems are important tools for an advanced control of the MHD instabilities in fusion plasmas, both for the suppression of undesired modes, such as RWMs, and for the generation of external perturbations for ELM suppression. A good knowledge of the diffusion time through the machine wall of each external harmonics is necessary for reaching optimal performances of the feedback algorithms.A correct theoretical estimation is not easy due the presence of three-dimensional mechanical structures in the devices, such as shell cuts and external conductive structures that need to be considered. Identification of differences in the vertical and horizontal diffusion time are not simple from a theoretical point of view.This work will present a relatively simple technique to experimentally estimate the diffusion time for each harmonic. The technique is based on the generation of rotating external magnetic perturbations in vacuum and on the quantification of the wall screening from the measured field inside the wall. The technique will be able to quantify possible differences among the horizontal and vertical diffusion time. In the final part of the work, the comparison with the results obtained with a closed-loop identification algorithm of the machine plant will be discussed.

  • 8.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Izzo, V.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Screening effect of plasma flow on resonant magnetic perturbations in EXTRAP T2R2012In: EPS Conf. Plasma Phys., EPS Int. Congr. Plasma Phys., 2012, 365-368 p.Conference paper (Refereed)
  • 9.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Khan, Waqas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    The effect of external control fields on tearing mode dynamics2011In: Proceedings of the 38th European Physical Society Conference on Plasma Physics, 2011, 1220-1223 p.Conference paper (Refereed)
  • 10.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tearing mode velocity braking due to resonant magnetic perturbations2012In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 52, no 10, 103014- p.Article in journal (Refereed)
    Abstract [en]

    The effect of resonant magnetic perturbations (RMPs) on the tearing mode (TM) velocity is studied in EXTRAP T2R. Experimental results show that the RMP produces TM braking until a new steady velocity or wall locking is reached. The braking is initially localized at the TM resonance and then spreads to the other TMs and to the rest of the plasma producing a global velocity reduction via the viscous torque. The process has been used to experimentally estimate the kinematic viscosity profile, in the range 2-40 m 2 s -1, and the electromagnetic torque produced by the RMP, which is strongly localized at the TM resonance. Experimental results are then compared with a theoretical model which gives a reasonable qualitative explanation of the entire process.

  • 11.
    Frassinetti, Lorenzo
    et al.
    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.
    Olofsson, Erik
    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.
    Brunsell, Per
    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.
    Drake, James robert
    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.
    Implementation of advanced feedback control algorithms for controlled resonant magnetic perturbation physics studies on EXTRAP T2R2011In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 51, no 6, 063018- p.Article in journal (Refereed)
    Abstract [en]

    The EXTRAP T2R feedback system (active coils, sensor coils and controller) is used to study and develop new tools for advanced control of the MHD instabilities in fusion plasmas. New feedback algorithms developed in EXTRAP T2R reversed-field pinch allow flexible and independent control of each magnetic harmonic. Methods developed in control theory and applied to EXTRAP T2R allow a closed-loop identification of the machine plant and of the resistive wall modes growth rates. The plant identification is the starting point for the development of output-tracking algorithms which enable the generation of external magnetic perturbations. These algorithms will then be used to study the effect of a resonant magnetic perturbation (RMP) on the tearing mode (TM) dynamics. It will be shown that the stationary RMP can induce oscillations in the amplitude and jumps in the phase of the rotating TM. It will be shown that the RMP strongly affects the magnetic island position.

  • 12.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Resonant magnetic perturbation effect on tearing mode dynamics2010In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, no 3, 035005- p.Article in journal (Refereed)
    Abstract [en]

    The effect of a resonant magnetic perturbation (RMP) on the tearing mode (TM) dynamics is experimentally studied in the EXTRAP T2R device. EXTRAP T2R is equipped with a set of sensor coils and active coils connected by a digital controller allowing a feedback control of the magnetic instabilities. The recently upgraded feedback algorithm allows the suppression of all the error field harmonics but keeping a selected harmonic to the desired amplitude, therefore opening the possibility of a clear study of the RMP effect on the corresponding TM. The paper shows that the RMP produces two typical effects: (1) a weak oscillation in the TM amplitude and a modulation in the TM velocity or (2) a strong modulation in the TM amplitude and phase jumps. Moreover, the locking mechanism of a TM to a RMP is studied in detail. It is shown that before the locking, the TM dynamics is characterized by velocity modulation followed by phase jumps. Experimental results are reasonably explained by simulations obtained with a model.

  • 13.
    Frassinetti, Lorenzo
    et al.
    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.
    Olofsson, Erik
    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.
    Khan, Muhammad Waqas Mehmood
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Brunsell, Per
    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.
    Drake, James R.
    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.
    Controlled Resonant Magnetic Perturbation Physics Studies on EXTRAP T2R2010In: Proc. 23 rd IAEA Fusion Energy Conference, IAEA , 2010Conference paper (Refereed)
  • 14.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fridström, Richard
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Setiadi, Agung Chris
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Volpe, F. A.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A method for the estimate of the wall diffusion for non-axisymmetric fields using rotating external fields2013In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, no 8, 084001- p.Article in journal (Refereed)
    Abstract [en]

    A new method for the estimate of the wall diffusion time of non-axisymmetric fields is developed. The method based on rotating external fields and on the measurement of the wall frequency response is developed and tested in EXTRAP T2R. The method allows the experimental estimate of the wall diffusion time for each Fourier harmonic and the estimate of the wall diffusion toroidal asymmetries. The method intrinsically considers the effects of three-dimensional structures and of the shell gaps. Far from the gaps, experimental results are in good agreement with the diffusion time estimated with a simple cylindrical model that assumes a homogeneous wall. The method is also applied with non-standard configurations of the coil array, in order to mimic tokamak-relevant settings with a partial wall coverage and active coils of large toroidal extent. The comparison with the full coverage results shows good agreement if the effects of the relevant sidebands are considered.

  • 15.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik. J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Khan, Muhammad Waqas Mehmood
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Experimental Studies of the Plasma Response to Applied Nonaxisymmetric External Magnetic Perturbations in EXTRAP T2R2012In: 24th IAEA Fusion Energy Conference, 2012, EX/P4-21- p.Conference paper (Refereed)
  • 16.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sun, Y.
    Khan, Muhammad Waqas Mehmood
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Flow braking due to non-resonant external perturbations in EXTRAP T2R and comparison   with neoclassical toroidal viscosity torque2012In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics, 2012, 1190-1193 p.Conference paper (Refereed)
  • 17.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sun, Y
    Khan, Muhammad Waqas Mehmood
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Screening effect of plasma flow on RMPs in EXTRAP T2R2012In: 39th European Physical Society (EPS) Conference on Plasma Physics, 2012, P1.067- p.Conference paper (Refereed)
  • 18.
    Khan, Muhammad Waqas Mehmood
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Braking of Plasma Rotation by Non-axisymmetric Magnetic Fields in EXTRAP T2R2011In: Proceedings of the 38th European Physical Society Conference on Plasma Physics, 2011, 841-844 p.Conference paper (Refereed)
  • 19. Martin, P.
    et al.
    Puiatti, M. E.
    Agostinetti, P.
    Agostini, M.
    Alonso, J. A.
    Antoni, V.
    Apolloni, L.
    Auriemma, F.
    Avino, F.
    Barbalace, A.
    Barbisan, M.
    Barbui, T.
    Barison, S.
    Barp, M.
    Baruzzo, M.
    Bettini, P.
    Bigi, M.
    Bilel, R.
    Boldrin, M.
    Bolzonella, T.
    Bonfiglio, D.
    Bonomo, F.
    Brombin, M.
    Buffa, A.
    Bustreo, C.
    Canton, A.
    Cappello, S.
    Carralero, D.
    Carraro, L.
    Cavazzana, R.
    Chacon, L.
    Chapman, B.
    Chitarin, G.
    Ciaccio, G.
    Cooper, W. A.
    Dal Bello, S.
    Dalla Palma, M.
    Delogu, R.
    De Lorenzi, A.
    Delzanno, G. L.
    De Masi, G.
    De Muri, M.
    Dong, J. Q.
    Escande, D. F.
    Fantini, F.
    Fasoli, A.
    Fassina, A.
    Fellin, F.
    Ferro, A.
    Fiameni, S.
    Finn, J. M.
    Finotti, C.
    Fiorentin, A.
    Fonnesu, N.
    Framarin, J.
    Franz, P.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Furno, I.
    Furno Palumbo, M.
    Gaio, E.
    Gazza, E.
    Ghezzi, F.
    Giudicotti, L.
    Gnesotto, F.
    Gobbin, M.
    Gonzales, W. A.
    Grando, L.
    Guo, S. C.
    Hanson, J. D.
    Hidalgo, C.
    Hirano, Y.
    Hirshman, S. P.
    Ide, S.
    In, Y.
    Innocente, P.
    Jackson, G. L.
    Kiyama, S.
    Liu, S. F.
    Liu, Y. Q.
    Lòpez Bruna, D.
    Lorenzini, R.
    Luce, T. C.
    Luchetta, A.
    Maistrello, A.
    Manduchi, G.
    Mansfield, D. K.
    Marchiori, G.
    Marconato, N.
    Marcuzzi, D.
    Marrelli, L.
    Martini, S.
    Matsunaga, G.
    Martines, E.
    Mazzitelli, G.
    McCollam, K.
    Momo, B.
    Moresco, M.
    Munaretto, S.
    Novello, L.
    Okabayashi, M.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Paccagnella, R.
    Pasqualotto, R.
    Pavei, M.
    Peruzzo, S.
    Pesce, A.
    Pilan, N.
    Piovan, R.
    Piovesan, P.
    Piron, C.
    Piron, L.
    Pomaro, N.
    Predebon, I.
    Recchia, M.
    Rigato, V.
    Rizzolo, A.
    Roquemore, A. L.
    Rostagni, G.
    Ruzzon, A.
    Sakakita, H.
    Sanchez, R.
    Sarff, J. S.
    Sartori, E.
    Sattin, F.
    Scaggion, A.
    Scarin, P.
    Schneider, W.
    Serianni, G.
    Sonato, P.
    Spada, E.
    Soppelsa, A.
    Spagnolo, S.
    Spolaore, M.
    Spong, D. A.
    Spizzo, G.
    Takechi, M.
    Taliercio, C.
    Terranova, D.
    Theiler, C.
    Toigo, V.
    Trevisan, G. L.
    Valente, M.
    Valisa, M.
    Veltri, P.
    Veranda, M.
    Vianello, N.
    Villone, F.
    Wang, Z. R.
    White, R. B.
    Xu, X. Y.
    Zaccaria, P.
    Zamengo, A.
    Zanca, P.
    Zaniol, B.
    Zanotto, L.
    Zilli, E.
    Zollino, G.
    Zuin, M.
    Overview of the RFX-mod fusion science programme2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 10, 104018- p.Article, review/survey (Refereed)
    Abstract [en]

    This paper reports the highlights of the RFX-mod fusion science programme since the last 2010 IAEA Fusion Energy Conference. The RFX-mod fusion science programme focused on two main goals: exploring the fusion potential of the reversed field pinch (RFP) magnetic configuration and contributing to the solution of key science and technology problems in the roadmap to ITER. Active control of several plasma parameters has been a key tool in this endeavour. New upgrades on the system for active control of magnetohydrodynamic (MHD) stability are underway and will be presented in this paper. Unique among the existing fusion devices, RFX-mod has been operated both as an RFP and as a tokamak. The latter operation has allowed the exploration of edge safety factor q edge < 2 with active control of MHD stability and studies concerning basic energy and flow transport mechanisms. Strong interaction has continued with the stellarator community in particular on the physics of helical states and on three-dimensional codes.

  • 20.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Closed-loop control and identification of resistive shell magnetohydrodynamics for the reversed-field pinch2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    It is demonstrated that control software updates for the magnetic confinement fusion experiment EXTRAP T2R can enable novel studies of plasma physics. Specifically, it is shown that the boundary radial magnetic field in T2R can be maintained at finite levels by feedback. System identification methods to measure in situ magnetohydrodynamic stability are developed and applied with encouraging results. Subsequently, results from closed-loop identification are used for retooling the T2R regulator. The track of research here pursued could possibly be relevant for future thermonuclear fusion reactors.

  • 21.
    Olofsson, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Controlled magnetohydrodynamic mode sustainment in the reversed-field pinch: Theory, design and experiments2009In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 84, no 7-11, 1455-1459 p.Article in journal (Refereed)
    Abstract [en]

    A novel control system design for magnetohydrodynamic (MHD) resistive-wall mode (RWM) stabilization is developed from the viewpoint of process control. The engineering approach assumed consists of system identification, selection of feedback interconnections, and subsequently, associated feedback gain tuning. A design for general output tracking is devised, implemented and experimentally verified to be capable of sustaining MHD modes in the reversed-field pinch (RFP) machine EXTRAP-T2R. In principle, by active feedback. the plasma column boundary is forced to 'user-specified' helicities of prescribed amplitudes and phases. Experimental success is mainly attributed to careful identification of local magnetic field diffusion time-constants, and individual actuator channel peripheral dynamics. Addition of functionality and key features of this new MHD feedback system software might provide a versatile tool for experimental plasma dynamics and innovative MHD stability research.

  • 22.
    Olofsson, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Closed-loop direct parametric identification of magnetohydrodynamic normal modes spectra in EXTRAP-T2R reversed-field pinch2009In: 2009 IEEE CONTROL APPLICATIONS CCA & INTELLIGENT CONTROL, 2009, 1449-1454 p.Conference paper (Refereed)
    Abstract [en]

    The reversed-field pinch (RFP) EXTRAP-T2R (T2R) is a plasma physics experiment with particular relevance for magnetic confinement fusion (MCF) research. T2R is very well equipped for investigations of magnetohydrodynamic (MHD) instabilities known as resistive-wall modes (RWMs), growing on a time-scale set by a surrounding non-perfectly conducting shell. The RWM instability is also subject of intense research in tokamak experiments (another MCF configuration). Recently, multiple RWMs have been stabilized in T2R using arrays of active (current-carrying) and sensor (voltage-measuring) coils equidistributed on the shell. In this paper, the MHD normal modes dynamics is probed in the required feedback operation by simultaneously, and pseudo-randomly, exciting the spectrum in the spatial sense. Spectra are then extracted by prediction-error minimization based on an observer that tracks dynamically aliased modes and the results thus obtained are related, and compared, to established linear MHD stability theory. This pioneer study at T2R is, arguably, appealling both to plasma physicists and automatic control staff.

  • 23.
    Olofsson, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Closed-loop identification and controller reconfiguration for EXTRAP T2R reversed-field pinch2009In: 2009 23RD IEEE/NPSS SYMPOSIUM ON FUSION ENGINEERING, NEW YORK: IEEE , 2009, 229-232 p.Conference paper (Refereed)
    Abstract [en]

    We briefly summarize a supposedly efficient novel method for measuring the external plasma response as applied to the inherently unstable reversed-field pinch EXTRAP T2R. The set of parameters estimated with this particular method is then harvested and fed as input to a discrete-time fixed-order fast fourier transform decoupled multi-input-multi-output controller synthesis. The thus reconfigured feedback system is implemented and experimentally tested on the real plant T2R. A particular and intended behaviour is observed, it seems, from these first-deployment results.

  • 24.
    Olofsson, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Closed-Loop System Identification and Controller Reconfiguration for EXTRAP T2R Reversed-Field Pinch2010In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, no 3, 365-370 p.Article in journal (Refereed)
    Abstract [en]

    We first briefly summarize a supposedly efficient novel method for measuring the external plasma response as applied to the inherently unstable reversed-field pinch EXTRAP T2R. Second, the set of parameters estimated with this particular method is harvested and fed as input to a discrete-time fixed-order fast-Fourier-transform-decoupled multi-input-multioutput controller synthesis. The thus reconfigured feedback system is implemented and experimentally tested on the real plant T2R. The recorded first-deployment results are encouraging. The overall methodology followed throughout this paper is emphasized and strongly exemplifies applied process control thinking for the stabilization of magnetically confined toroidal plasmas.

  • 25.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Extended benchmark results for impulse response estimation2013In: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, 7168-7173 p.Conference paper (Refereed)
    Abstract [en]

    Recent attention has been given to the use of regularised least-squares methods for improving the quality of classical impulse response estimates from short/noisy datasets. This paper significantly augments and contextualises previously reported benchmark results by inclusion of a larger set of standard and non-standard methods in the comparison. The numerical experiments are summarised using several metrics. There is no obvious winner method.

  • 26.
    Olofsson, K Erik J
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Nonaxisymmetric experimental modal analysis and control of resistive wall MHD in RFPs: System identification and feedback control for the reversed-field pinch2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The reversed-field pinch (RFP) is a device for magnetic confinement of fusion plasmas. The main objective of fusion plasma research is to realise cost-effective thermonuclear fusion power plants. The RFP is highly unstable as can be explained by the theory of magnetohydrodynamics (MHD). Feed-back control technology appears to enable a robustly stable RFP operation.  Experimental control and identification of nonaxisymmetric multimode MHD is pursued in this thesis. It is shown that nonparametric multivariate identification methods can be utilised to estimate MHD spectral characteristics from plant-friendly closed-loop operational input-output data. It is also shown that accurate tracking of the radial magnetic field boundary condition is experimentally possible in the RFP. These results appear generically useful as tools in both control and physics research in magnetic confinement fusion.

  • 27.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Initial reference-spectrum resistive wall mode feedback control simulation and multivariable design2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, 728-731 p.Conference paper (Refereed)
  • 28.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Experimental modal analysis of resistive wall toroidal pinch plasma dynamics2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 7, 072003- p.Article in journal (Refereed)
    Abstract [en]

    The linearized magnetofluid dynamics of a magnetically confined reversed-field pinch plasma is extracted from a set of perturbative randomized nondestructive experiments. The spectrum of the generically estimated linear time-invariant system is compared to solutions of the corresponding eigenvalue problems formed by the ideal magnetohydrodynamic model. Stable and unstable nonresonant resistive wall modes are accurately identified.

  • 29.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Measurements of the vacuum-plasma response in EXTRAP T2R using generic closed-loop subspace system identification2012In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 87, no 12, 1926-1929 p.Article in journal (Refereed)
    Abstract [en]

    A multibatch formulation of a multi-input multi-output closed-loop subspace system identification method is employed for the purpose of obtaining control-relevant models of the vacuum-plasma response in the magnetic confinement fusion experiment EXTRAP T2R. The accuracy of the estimate of the plant dynamics is estimated by computing bootstrap replication statistics of the dataset. It is seen that the thus identified models exhibit both predictive capabilities and physical spectral properties.

  • 30.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A first attempt at few coils and low-coverage resistive wall mode stabilization of EXTRAP T2R2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 9, 094005- p.Article in journal (Refereed)
    Abstract [en]

    The reversed-field pinch features resistive-shell-type instabilities at any (vanishing and finite) plasma pressure. An attempt to stabilize the full spectrum of these modes using both (i) incomplete coverage and (ii) few coils is presented. Two empirically derived model-based control algorithms are compared with a baseline guaranteed suboptimal intelligent-shell-type (IS) feedback. Experimental stabilization could not be achieved for the coil array subset sizes considered by this first study. But the model-based controllers appear to significantly outperform the decentralized IS method.

  • 31.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Predictor-based multivariable closed-loop system identification of the EXTRAP T2R reversed field pinch external plasma response2011In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 53, no 8, 084003- p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 32.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Witrant, Emmanuel
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Synthesis and operation of an FFT-decoupled fixed-order reversed-field pinch plasma control system based on identification data2010In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, no 10, 104005- p.Article in journal (Refereed)
    Abstract [en]

    Recent developments and applications of system identification methods for the reversed-field pinch (RFP) machine EXTRAP T2R have yielded plasma response parameters for decoupled dynamics. These data sets are fundamental for a real-time implementable fast Fourier transform (FFT) decoupled discrete-time fixed-order strongly stabilizing synthesis as described in this work. Robustness is assessed over the data set by bootstrap calculation of the sensitivity transfer function worst-case H(infinity)-gain distribution. Output tracking and magnetohydrodynamic mode m = 1 tracking are considered in the same framework simply as two distinct weighted traces of a performance channel output-covariance matrix as derived from the closed-loop discrete-time Lyapunov equation. The behaviour of the resulting multivariable controller is investigated with dedicated T2R experiments.

  • 33.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vector dither experiment design and direct parametric identification of reversed-field pinch normal modes2009In: Proceedings of the IEEE Conference on Decision and Control, 2009, 1348-1353 p.Conference paper (Refereed)
    Abstract [en]

    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.

  • 34.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A practical approach to input design for modal analysis using subspace methods2012In: 16th IFAC Symposium on System Identification, IFAC , 2012, 362-367 p.Conference paper (Refereed)
    Abstract [en]

    A basic class of multivariate system identification input design methods is proposed. Only reliable numerical linear algebra is used. The underlying idea is to inject energy into the invariant eigenspace for a subset of preestimated plant eigenvalues. Standard Schur pseudotriangular factorisation is used to pretarget a subsequent singular value decomposition. Explicit state-space formulas are given. Examples indicate that the approach may be useful in some practical applications. The approach may be considered user-friendly.

  • 35.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Cascade and multibatch subspace system identification for multivariate vacuum-plasma response characterisation2011In: Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC11), 2011, 2614-2619 p.Conference paper (Refereed)
    Abstract [en]

    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.

     

  • 36.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Closed-loop MIMO ARX estimation of concurrent external plasma response eigenmodes in magnetic confinement fusion2010In: Proceedings of the 49th Conference on Decision and Control (CDC’10), 2010, 2954-2959 p.Conference paper (Refereed)
    Abstract [en]

    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.

  • 37.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Soppelsa, Anton
    Bolzonella, Tommaso
    Marchiori, Giuseppe
    Subspace identification analysis of RFX and T2R reversed-field pinches2013In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 21, no 7, 917-929 p.Article in journal (Refereed)
    Abstract [en]

    Input-output datasets from two magnetic confinement fusion (MCF) experiments of the reversed-field pinch (RFP) type are examined. The RFP datasets, which are samples of the distributed magnetic field dynamics, are naturally divided into many smaller batches due to the pulsed-plasma operation of the experiments. The two RFP experiments considered are (i) EXTRAP T2R (T2R) with 64 inputs and 64 outputs and (ii) RFX-mod (RFX) with 192 inputs and 192 outputs. Both T2R and RFX are magnetohydrodynamically unstable and operates under magnetic feedback with optional dither injection. Using subspace system identification techniques and randomised cross-validation (CV) methods to minimise the generalisation error, state-space orders of the empirical systems are suggested. These system orders are compared to "stabilisation diagrams" commonly used in experimental modal analysis practice. The relation of the CV system order to the decay of the singular values from the subspace method is observed. Both (i) stable vacuum diffusion and (ii) unstable plasma response datasets are analysed. Apparent simulation and prediction errors are quantified for both cases using a deviation-accounted-for index. These results are purely data-driven. A simple approach towards exploitation of the subspace techniques for finite-element model refinement and data confrontation is presented.

  • 38.
    Olofsson, K Erik J
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Witrant, Emmanuel
    UJF/INPG.
    Briat, Corentin
    UJF/INPG.
    Niculescu, Silviu-Iulian
    CNRS/Supelec Laboratoire des Signaux et Systemes, Gif-sur-Yvette, France.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stability analysis and model-based control in EXTRAP-T2R with time-delay compensation2008In: Proceedings of the 47th IEEE Conference on Decision and Control, Cancun, Mexico, Dec. 9-11, 2008, IEEE conference proceedings, 2008, 2044-2049 p.Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the stability problems and control issues that occur in a reversed-field pinch (RFP) device, EXTRAP-T2R (T2R), used for research in fusion plasma physics and general plasma (ionized gas) dynamics. The plant exhibits, among other things, magnetohydrodynamic instabilities known as resistive-wall modes (RWMs), growing on a time-scale set by a surrounding non-perfectly conducting shell.We propose a novel model that takes into account experimental constraints, such as the actuators dynamics and control latencies, which lead to a multivariable time-delay model of the system. The open-loop field-error characteristics are estimated and a stability analysis of the resulting closed-loop delay differential equation (DDE) emphasizes the importance of the delay effects. We then design a structurally constrained optimal PID controller by direct eigenvalue optimization (DEO) of this DDE. The presented results are substantially based on and compared with experimental data.

  • 39. Suttrop, W.
    et al.
    Hahn, D.
    Herrman, A.
    Rott, M.
    Streibl, B.
    Treutterer, W.
    Vierle, D.
    Yadikin, D.
    Zammuto, I.
    Gaio, E.
    Toigo, V.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Physical description of external circuitry for Resistive Wall Mode control in ASDEX Upgrade2009In: 36th European Physical Society Conference on Plasma Physics / [ed] M. Mateev, E. Benova, 2009, P-1.165- p.Conference paper (Refereed)
  • 40. Volpe, F. A.
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Error field assessment from driven rotation of stable external kinks at EXTRAP-T2R reversed field pinch2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 4, 043018- p.Article in journal (Refereed)
    Abstract [en]

    A new non-disruptive error field (EF) assessment technique not restricted to low density and thus low beta was demonstrated at the EXTRAP-T2R reversed field pinch. Stable and marginally stable external kink modes of toroidal mode number n = 10 and n = 8, respectively, were generated, and their rotation sustained, by means of rotating magnetic perturbations of the same n. Due to finite EFs, and in spite of the applied perturbations rotating uniformly and having constant amplitude, the kink modes were observed to rotate non-uniformly and be modulated in amplitude. This behaviour was used to precisely infer the amplitude and approximately estimate the toroidal phase of the EF. A subsequent scan permitted to optimize the toroidal phase. The technique was tested against deliberately applied as well as intrinsic EFs of n = 8 and 10. Corrections equal and opposite to the estimated error fields were applied. The efficacy of the error compensation was indicated by the increased discharge duration and more uniform mode rotation in response to a uniformly rotating perturbation. The results are in good agreement with theory, and the extension to lower n, to tearing modes and to tokamaks, including ITER, is discussed.

  • 41. Volpe, F
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, P
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, E
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Error Field Assessment from Driven Mode Rotation: Results from Extrap-T2R Reversed-Field-Pinch and Perspectives for ITER2012In: 54th Meeting of the APS Division of Plasma Physics, November 2012,  Providence, USA, 2012Conference paper (Refereed)
    Abstract [en]

    A new ITER-relevant non-disruptive error field (EF) assessment technique not restricted to low density and thus low beta was demonstrated at the Extrap-T2R reversed field pinch. Resistive Wall Modes (RWMs) were generated and their rotation sustained by rotating magnetic perturbations. In particular, stable modes of toroidal mode number n=8 and 10 and unstable modes of n=1 were used in this experiment. Due to finite EFs, and in spite of the applied perturbations rotating uniformly and having constant amplitude, the RWMs were observed to rotate non-uniformly and be modulated in amplitude (in the case of unstable modes, the observed oscillation was superimposed to the mode growth). This behavior was used to infer the amplitude and toroidal phase of n=1, 8 and 10 EFs. The method was first tested against known, deliberately applied EFs, and then against actual intrinsic EFs. Applying equal and opposite corrections resulted in longer discharges and more uniform mode rotation, indicating good EF compensation. The results agree with a simple theoretical model. Extensions to tearing modes, to the non-uniform plasma response to rotating perturbations, and to tokamaks, including ITER, will be discussed.

1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf