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  • 1.
    Brunsell, Per R.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Hedqvist, Anders
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Yadikin, Dimitry
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R2006Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 11, s. 904-913Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size.

  • 2.
    Brunsell, Per. R.
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, Jenny-Ann
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, Dimitry
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Resistive wall modes in the EXTRAP T2R reversed-field pinch2003Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 10, s. 3823-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Resistive wall modes (RWM) in the reversed field pinch are studied and a detailed comparison of experimental growth rates and linear magnetohydrodynamic (MHD) theory is made. RWM growth rates are experimentally measured in the thin shell device EXTRAP T2R [P. R. Brunsell , Plasma Phys. Controlled Fusion 43, 1 (2001)]. Linear MHD calculations of RWM growth rates are based on experimental equilibria. Experimental and linear MHD RWM growth rate dependency on the equilibrium profiles is investigated experimentally by varying the pinch parameter Theta=B-theta(a)/<B-phi> in the range Theta=1.5-1.8. Quantitative agreement between experimental and linear MHD growth rates is seen. The dominating RWMs are the internal on-axis modes (having the same helicity as the central equilibrium field). At high Theta, external nonresonant modes are also observed. For internal modes experimental growth rates decrease with Theta while for external modes, growth rates increase with Theta. The effect of RWMs on the reversed-field pinch plasma performance is discussed.

  • 3.
    Brunsell, Per R.
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gregoratto, D.
    Bolzonella, T.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Luchetta, A.
    Malmberg, Jenny-Ann
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Manduchi, G.
    Marchiori, G.
    Liu, Y.
    Ortolani, S.
    Paccagnella, R.
    First results from intelligent shell experiments with partial coil coverage in the EXTRAP T2R reversed field pinch2004Ingår i: Europhysics Conf. Abstracts Vol 29C, 2004, s. P-5.190-Konferensbidrag (Refereegranskat)
  • 4.
    Brunsell, Per
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, Dimitry
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gregoratto, D.
    Paccagnella, R.
    Bolzonella, T.
    Cavinato, M.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Luchetta, A.
    Manduchi, G.
    Marchiori, G.
    Marrelli, L.
    Martin, P.
    Masiello, A.
    Milani, F.
    Ortolani, S.
    Spizzo, G.
    Zanca, P.
    Feedback Stabilization of Multiple Resistive Wall Modes2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, nr 22, s. 225001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Active feedback stabilization of multiple independent resistive wall modes is experimentally demonstrated in a reversed-field pinch plasma. A reproducible simultaneous suppression of several nonresonant resistive wall modes is achieved. Coupling of different modes due to the limited number of the feedback coils is observed in agreement with theory. The feedback stabilization of nonresonant RWMs also has an effect on tearing modes that are resonant in the central plasma, leading to a significant prolongation of the discharge pulse.

  • 5.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Marchiori, Giuseppe
    Feedback stabilization of resistive wall modes in a reversed-field pinch2005Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, nr 9, s. 092508-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An array of saddle coils having Nc =16 equally spaced positions along the toroidal direction has been installed for feedback control of resistive wall modes (RWMs) on the EXTRAP T2R reversed-field pinch [P. R. Brunsell, H. Bergsaker, M. Cecconello, Plasma Phys. Controlled Fusion 43, 1457 (2001)]. Using feedback, multiple nonresonant RWMs are simultaneously suppressed for three to four wall times. Feedback stabilization of RWMs results in a significant prolongation of the discharge duration. This is linked to a better sustainment of the plasma and tearing mode toroidal rotation with feedback. Due to the limited number of coils in the toroidal direction, pairs of modes with toroidal mode numbers n, n′ that fulfill the condition ∫n- n′ ∫ = Nc are coupled by the feedback action from the discrete coil array. With only one unstable mode in a pair of coupled modes, the suppression of the unstable mode is successful. If two modes are unstable in a coupled pair, two possibilities exist: partial suppression of both modes or, alternatively, complete stabilization of one target mode while the other is left unstable.

  • 6.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Zanca, P.
    Active control of multiple resistive wall modes2005Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, nr 12 B, s. B25-B36Artikel i tidskrift (Refereegranskat)
    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.

  • 7. Cavinato, M.
    et al.
    Gregoratto, D.
    Marchiori, G.
    Paccagnella, R.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Comparison of strategies and regulator design for active control of MHD modes2005Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 74, nr 1-4, s. 549-553Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A system of evenly spaced poloidal arrays of saddle coils was recently installed on the reversed field pinch device EXTRAP T2R to perform experiments on the active control of MHD modes. The implementation of different control strategies, such as "intelligent shell" and "mode control", was made possible by a flexible digital control system. After giving some results on the performances of the innermost coil current control loop, two versions of "mode control" recently tested on the machine are presented. In the "wise shell" approach, equilibrium related modes are ruled out and a systematic increase of the pulse length is obtained. In a second, more model based, approach, a mode estimator/controller is designed aiming at a full state feedback by including modes, which are not directly measurable due to the limited number of available real-time signals.

  • 8.
    Cecconello, Marco
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Rotation evolution of tearing modes during feedback stabilization of resistive wall modes in a reversed field pinch2005Konferensbidrag (Refereegranskat)
  • 9.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hedqvist, Anders
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Experiments on feedback control of multiple resistive wall modes comparing different active coil arrays and sensor types2006Ingår i: IAEA-F1-CN-149, 2006, s. Paper EX/P8-11-Konferensbidrag (Refereegranskat)
  • 10.
    Drake, James Robert
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Brunsell, Per R
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, Jenny-A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gregoratto, D
    Paccagnella, R
    Bolzonella, T
    Manduchi, G
    Marrelli, L
    Ortolani, S
    Spizzo, G
    Zanca, P
    Bondeson, A
    Liu, Y Q
    Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch2004Ingår i: IAEA-CN-116, 2004, s. Paper EX/P2-20-Konferensbidrag (Refereegranskat)
  • 11.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Yadikin, Dimitry
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Malmberg, Jenny
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Liu, Y.
    Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch2005Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, nr 7, s. 557-564Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Active feedback control of resistive wall modes (RWMs) has been demonstrated in the EXTRAP T2R reversed-field pinch experiment. The control system includes a sensor consisting of an array of magnetic coils (measuring mode harmonics) and an actuator consisting of a saddle coil array (producing control harmonics). Closed-loop (feedback) experiments using a digital controller based on a real time Fourier transform of sensor data have been studied for cases where the feedback gain was constant and real for all harmonics (corresponding to an intelligent-shell) and cases where the feedback gain could be set for selected harmonics, with both real and complex values (targeted harmonics). The growth of the dominant RWMs can be reduced by feedback for both the intelligent-shell and targeted-harmonic control systems. Because the number of toroidal positions of the saddle coils in the array is half the number of the sensors, it is predicted and observed experimentally that the control harmonic spectrum has sidebands. Individual unstable harmonics can be controlled with real gains. However if there are two unstable mode harmonics coupled by the sideband effect, control is much less effective with real gains. According to the theory, complex gains give better results for (slowly) rotating RWMs, and experiments support this prediction. In addition, open loop experiments have been used to observe the effects of resonant field errors applied to unstable, marginally stable and robustly stable modes. The observed effects of field errors are consistent with the thin-wall model, where mode growth is proportional to the resonant field error amplitude and the wall penetration time for that mode harmonic.

  • 12.
    Yadikin, Dimitry
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Feedback control of resistive wall modes in the reversed field pinch2004Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    A wide range of unstable current driven MHD modes is present in the re- versed τeld pinch (RFP) conτguration. An ideally conducting wall facing the plasma can stabilize the ideal MHD modes. In the presence of a resistive wall characterized by the wall time τw, fast mode rotation with the frequency exceeding the inverse wall time gives stabilization for resistive MHD modes. The ideal MHD modes in the RFP are non-rotating modes and can not be stabilized by the resistive wall. Instead they are converted into resistive wall modes (RWM) growing with a growth rate proportional to the inverse of the wall time τw. EXTRAP T2R is an RFP device equipped with a thin resistive wall having the wall time shorter than the plasma pulse duration τw < τp. This feature allows the study of non-resonant non-rotating resistive wall modes. Resistive wall modes dynamics has been studied in EXTRAP T2R . RWM growth rates has been measured and compared with linear MHD stability calculations. Quantitative agreement is observed. In the case τw < τp the RWM can cause discharge degradation and should be stabilized. Active feedback is the way to stabilize the RWM in the RFP. An intelligent shell scheme is one possible feedback scenario. An active feed- back system including a set of sensors and discrete active coils is installed in EXTRAP T2R. The intelligent shell tries to keep the magnetic flux zero at the positions of the sensor. The analog PID controller for the intelligent shell feedback scheme has been studied. A model of the active control system was developed and comparison with the experimental results showed good agree- ment. Encouraging experimental results on the active feedback stabilization of multiple RWMs in the RFP plasmas were obtained.

  • 13.
    Yadikin, Dimitry
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Paccagnella, R.
    Advanced feedback control methods in EXTRAP T2R2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 7, s. 072109-Artikel i tidskrift (Refereegranskat)
    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.

  • 14.
    Yadikin, Dimitry
    et al.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Brunsell, Per. R.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Malmberg, Jenny-Ann
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Martin, P.
    Milani, F.
    Marrelli, L.
    Drake, James Robert
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Marchiori, G.
    Feedback controller for saddle coils for suppression of resistive wall modes in EXTRAP T2R2004Ingår i: 31st European Physical Society Conference on Controlled Fusion and Plasma Physics, 2004Konferensbidrag (Refereegranskat)
  • 15.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Resistive Wall Mode Stability and Control in the Reversed Field Pinch2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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

  • 16.
    Yadikin, Dmitriy
    et al.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Comparision of experimental resistive wall mode growth rates in the EXTRAP T2R reversed field pinch with linear theory2003Ingår i: 30th Eruopean Physical Society Conference on Controlled Fusion and Plasma Physics: St. Petersburg 2003, 2003Konferensbidrag (Refereegranskat)
  • 17.
    Yadikin, Dmitriy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Intelligent shell feedback control in EXTRAP T2R reversed field pinch with partial coverage of the toroidal surface by a discrete active coil array2006Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr 1, s. 1-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An active feedback system is required for long pulse operation of the reversed field pinch (RFP) device to suppress resistive wall modes (RWMs). A general feature of a feedback system using a discrete active coil array is a coupling effect which arises when a set of side band modes determined by the number of active coils is produced. Recent results obtained on the EXTRAP T2R RFP demonstrated the suppression of independent m ≤ 1 RWMs using an active feedback system with a two-dimensional array of discrete active coils in the poloidal and toroidal directions. One of the feedback algorithms used is the intelligent shell feedback scheme. Active feedback systems having different number of active coils in the poloidal (Mc) and toroidal (N c) directions (Mc × Nc ≤ 2 × 32 and Mc × Nc ≤ 4 × 16) are studied. Different side band effects are seen for these configurations. A significant prolongation of the plasma discharge is achieved for the intelligent shell feedback scheme using the 2 × 32 active coil configuration. This is attributed to the side band sets including only one of the dominant unstable RWMs and avoiding coupling to resonant modes. Analog proportional-integral- derivative controllers are used in the feedback system. Regimes with different values of the proportional gain are studied. The requirement of the proportional-integral control for low proportional gain and proportional- derivative control for high proportional gain is seen in the experiments.

  • 18.
    Yadikin, Dmitriy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Intelligent shell feedback control of resistive wall modes in EXTRAP T2R2005Ingår i: 32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets: Europhysics Conference Abstracts, 2005, s. 1602-1605Konferensbidrag (Refereegranskat)
1 - 18 av 18
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