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  • 1. Antoni, V
    et al.
    Cavanazza, R
    Martines, E
    Serianni, G
    Spada, E
    Spolaore, M
    Vianello, N
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Bergsåker, Henric
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, Per R
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Regnoli, G
    Turbulent transport and plasma flow in the reversed field pinch2004In: IAEA-CN-116, 2004Conference paper (Refereed)
  • 2. Antoni, V.
    et al.
    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.
    Spada, E.
    Spolaore, M.
    Vianello, N.
    Bergsåker, Henric
    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.
    Cavazzana, R.
    Cecconello, Marco
    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.
    Martines, E.
    Serianni, G.
    Coherent structures and anomalous transport in reversed field pinch plasmas2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T122, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The results leading to the identification of coherent structures emerging from the background turbulence in the edge region of the reversed field pinch experiments EXTRAP-T2R and RFX are reviewed. These structures have traits of vortices in velocity field and blobs in density, and the reconstruction of their spatial structure and of their time evolution is discussed focusing on the analysis tools applied. The role of these structures in the particle anomalous transport is addressed, showing that their collisions can contribute up to 50% the total particle losses. This process is shown to be responsible for bursts in particle flux and it is found to set a characteristic collision time, which is in agreement with the statistical properties of laminar times for particle flux bursts.

  • 3.
    Brunsell, Per
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Bergsåker, Henric
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Gravestijn, Robert
    KTH, Superseded Departments, Physics.
    Hedqvist, Anders
    KTH, Superseded Departments, Physics.
    Malmberg, Jenny A.
    KTH, Superseded Departments, Alfvén Laboratory.
    Initial results from the rebuilt EXTRAP T2R RFP device2001In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 43, no 11, p. 1457-1470Article in journal (Refereed)
    Abstract [en]

    The EXTRAP T2R thin shell reversed-field pinch (RFP) device has recently resumed operation after a major rebuild including the replacement of the graphite armour with molybdenum limiters, a fourfold increase of the shell time constant, and the replacement of the helical coil used for the toroidal field with a conventional solenoid-type coil. Wall-conditioning using hydrogen glow discharge cleaning was instrumental for successful RFP operation. Carbon was permanently removed from the walls during the first week of operation. The initial results from RFP operation with relatively low plasma currents in the range I-p = 70-100 kA are reported. RFP discharges are sustained for more than three shell times. Significant improvements in plasma parameters are observed, compared to operation before the rebuild. There is a substantial reduction in the carbon impurity level. The electron density behaviour is more shot-to-shot reproducible. The typical density is n(e) = 0.5-1 x 10(19) m(-3). Monitors of H-alpha line radiation indicate that the plasma wall interaction is more toroidally symmetric and that there is less transient gas release from the wall. The minimum loop voltage is in the range V-t = 28-35 V, corresponding to a reduction by a factor of two to three compared to the value before the rebuild.

  • 4.
    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, p. 544-547Conference 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.

  • 5.
    Brunsell, Per R.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Yadikin, Dimitry
    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), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R2006In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 11, p. 904-913Article in journal (Refereed)
    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.

  • 6.
    Brunsell, Per. R.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny-Ann
    KTH, Superseded Departments, Alfvén Laboratory.
    Yadikin, Dimitry
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Resistive wall modes in the EXTRAP T2R reversed-field pinch2003In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 10, p. 3823-Article in journal (Refereed)
    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.

  • 7.
    Brunsell, Per R.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Yadikin, Dmitriy
    KTH, Superseded Departments, Alfvén Laboratory.
    Gregoratto, D.
    Bolzonella, T.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Luchetta, A.
    Malmberg, Jenny-Ann
    KTH, Superseded Departments, Alfvén Laboratory.
    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 pinch2004In: Europhysics Conf. Abstracts Vol 29C, 2004, p. P-5.190-Conference paper (Refereed)
  • 8.
    Brunsell, Per
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Yadikin, Dimitry
    KTH, Superseded Departments, Alfvén Laboratory.
    Gregoratto, D.
    Paccagnella, R.
    Bolzonella, T.
    Cavinato, M.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    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 Modes2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 22, p. 225001-Article in journal (Refereed)
    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.

  • 9.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    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), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Marchiori, Giuseppe
    Feedback stabilization of resistive wall modes in a reversed-field pinch2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 9, p. 092508-Article in journal (Refereed)
    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.

  • 10.
    Brunsell, Per
    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.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    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.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Zanca, P.
    Active control of multiple resistive wall modes2005In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, no 12 B, p. B25-B36Article in journal (Refereed)
    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.

  • 11.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Electron density and transport in EXTRAP T2R2002In: Proceedings of the 29th European Physical Society Conference on ControlledFusion and Plasma Physics, Montreux, 2002Conference paper (Other academic)
  • 12.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Experimental studies of confinement in the EXTRAP T2 and T2R reversed field pinches2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The confinement properties of fusion plasmas are affected bymagnetic and electrostatic fluctuations. The determination ofthe plasma confinement properties requires the measurement ofseveral global and local quantities such as the ion andelectron temperatures, the electron and neutral densityprofiles, the radiation emissivity profiles, the ohmic inputpower and the particle and heat diffusivities. The focus ofthis thesis is the study of the plasma confinement propertiesbased on measurements of these quantities under differentexperimental conditions.

    The studies have been carried out on the reversed fieldpinch experiments EXTRAP T2 and T2R at the AlfvénLaboratory, Royal Institute of Technology (KTH) in Stockholm.Studies carried out in EXTRAP T2 were focused on dynamoactivity and on the effect of phase alignment and locking tothe wall of magnetic instabilities. These were observed with adedicated imaging system. The experimental studies in EXTRAPT2R were focused on the measurement of the confinementproperties of different configurations. To this aim, a set ofdiagnostics were used some of which were upgraded, such as theinterferometer, while others were newly installed, such as aneutral particle energy analyser and a bolometer array.

    The dynamo, which is responsible for the plasma sustainment,involves resistive magnetohydrodynamic instabilities thatenhance stochastic transport. Furthermore, the plasmaconfinement properties are in general improved in the presenceof mode rotation. The possibility of reducing the stochastictransport and thereby further improving the confinement hasbeen demonstrated in a current profile control experiment.These results indicate that long pulse operations with aresisitive shell and current profile control are indeedfeasible.

    KeywordsEXTRAP T2, T2R, reversed field pinch, dynamo,energy confinement time, transport, CCD, bolometer,interferometer, neutral particle energy analyser, PPCD, MonteCarlo

  • 13.
    Cecconello, Marco
    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.
    Brunsell, Per 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.
    Yadikin, Dmitriy
    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.
    Rotation evolution of tearing modes during feedback stabilization of resistive wall modes in a reversed field pinch2005Conference paper (Refereed)
  • 14.
    Cecconello, Marco
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Brzozowski, Jerzy
    KTH, Superseded Departments, Alfvén Laboratory.
    Gravestijn, Robert
    KTH, Superseded Departments, Physics.
    Murari, A
    Total radiation losses studies in EXTRAP T2R2001In: Proceedings of the 28th European Physical Society Conference on Controlled Fusion and Plasma Physics, Madeira, 2001Conference paper (Other academic)
  • 15.
    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, p. 429-432Conference paper (Refereed)
  • 16.
    Cecconello, Marco
    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.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Brunsell, Per 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.
    Current profile modifications with active feedback stabilization of resistive wall modes in a reversed field pinch2006In: Proceedings of the 33rd European Physical Society Conference on Plasma Physics, 2006, p. 1680-1683Conference paper (Refereed)
  • 17.
    Cecconello, Marco
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny A.
    KTH, Superseded Departments, Alfvén Laboratory.
    Spizzo, G.
    Chapman, B. E.
    Gravestjin, Robert M.
    KTH, Superseded Departments, Physics.
    Franz, P.
    Piovesan, P.
    Martin, P.
    Drake, James R.
    KTH, Superseded Departments, Alfvén Laboratory.
    Current profile modification experiments in EXTRAP T2R2004In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 46, no 1, p. 145-161Article in journal (Refereed)
    Abstract [en]

    Pulsed poloidal current drive (PPCD) experiments have been conducted in the resistive shell EXTRAP T2R reversed-field pinch experiment. During the current profile modification phase, the fluctuation level of the m = 1 internally resonant tearing modes decreases, and the velocity of these modes increases. The m = 0 modes are not affected during PPCD, although termination occurs with a burst in the m = 0 amplitude. The PPCD phase is characterized by an increase in the central electron temperature (up to 380 eV) and in the soft x-ray signal. Spectroscopic observations confirm an increase in the central electron temperature. During PPCD, the plasma poloidal beta increases to 14%, and the estimated energy confinement time doubles, reaching 380 mus. The reduction in the fluctuation level and the corresponding increase in the energy confinement time are qualitatively consistent with a reduction in parallel transport along stochastic magnetic field lines.

  • 18.
    Cecconello, Marco
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny-Ann
    KTH, Superseded Departments, Alfvén Laboratory.
    Nielsen, P
    Pasqualotto, R
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling2002In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 44, no 8, p. 1625-1638Article in journal (Refereed)
    Abstract [en]

    An extensive investigation of the global confinement properties in different operating scenarios in the rebuilt EXTRAP T2R reversed-field pinch (RFP) experiment is reported here. In particular, the role of a fast gas puff valve system, used to control plasma density, on confinement is studied. Without gas puffing, the electron density decays below 0.5 x 10(19) M-3. The poloidal beta varies between 5% and 15%, decreasing at large I/N. The energy confinement time ranges from 70 to 225 mus. With gas puffing, the density is sustained at n(e) approximate to 1.5 x 10(19) m(-3). However, a general slight deterioration of the plasma performances is observed for the same values of I/N: the plasma becomes cooler and more radiative. The poloidal beta is comparable to that in the scenarios without puff but the energy confinement time drops ranging from 60 to 130 mus. The fluctuation level and the energy confinement time have been found to scale with the Lundquist number as S-0.05+/-0.07 and S0.5+/-0.1, respectively. Mode rotation is typical for all the discharges and rotation velocity is observed to increase with increasing electron diamagnetic velocity.

  • 19.
    Cecconello, Marco
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny-Ann
    KTH, Superseded Departments, Alfvén Laboratory.
    Sallander, Eva
    KTH, Superseded Departments, Alfvén Laboratory.
    Drake, Drake James
    KTH, Superseded Departments, Alfvén Laboratory.
    Self-organisation and intermittent coherent oscillations in the EXTRAP T2 reversed field pinch2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 65, no 1, p. 69-75Article in journal (Refereed)
    Abstract [en]

    Many reversed-field pinch (RFP) experiments exhibit a coherent oscillatory behaviour that is characteristic of discrete dynamo events and is associated with intermittent current profile self-organisation phenomena. However, in the vast majority of the discharges in the resistive shell RFP experiment EXTRAP T2, the dynamo activity does not show global, coherent oscillatory behaviour, The internally resonant tearing modes are phase-aligned and wall-locked resulting in a large localised magnetic perturbation. Equilibrium and plasma parameters have a level of high frequency fluctuations but the average values are quasi-steady. For some discharges, however, the equilibrium parameters exhibit the oscillatory behaviour characteristic of the discrete dynamo events. For these discharges, the trend observed in the tearing mode spectra, associated with the onset of the discrete relaxation event behaviour, is a relative higher amplitude of m = 0 mode activity and relative lower amplitude of the m = 1 mode activity compared with their average values. Global plasma parameters and model profile calculations for sample discharges representing the two types of relaxation dynamics are presented.

  • 20.
    Cecconello, Marco
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny-Ann
    KTH, Superseded Departments, Alfvén Laboratory.
    Spizzo, G
    Gravestijn, Robert
    KTH, Superseded Departments, Physics.
    Franz, P
    Martin, P
    Chapman, B
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Current profile control experiments in EXTRAP T2RManuscript (preprint) (Other academic)
  • 21.
    Cecconello, Marco
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Rotation in a reversed field pinch with active feedback stabilization of resistive wall modes2006In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, no 9, p. 1311-1331Article in journal (Refereed)
    Abstract [en]

    Active feedback stabilization of multiple resistive wall modes (RWMs) has been successfully proven in the EXTRAP T2R reversed field pinch. One of the features of plasma discharges operated with active feedback stabilization, in addition to the prolongation of the plasma discharge, is the sustainment of the plasma rotation. Sustained rotation is observed both for the internally resonant tearing modes (TMs) and the intrinsic impurity oxygen ions. Good quantitative agreement between the toroidal rotation velocities of both is found: the toroidal rotation is characterized by an acceleration phase followed, after one wall time, by a deceleration phase that is slower than in standard discharges. The TMs and the impurity ions rotate in the same poloidal direction with also similar velocities. Poloidal and toroidal velocities have comparable amplitudes and a simple model of their radial profile reproduces the main features of the helical angular phase velocity. RWMs feedback does not qualitatively change the TMs behaviour and typical phenomena such as the dynamo and the `slinky' are still observed. The improved sustainment of the plasma and TMs rotation occurs also when feedback only acts on internally non- resonant RWMs. This may be due to an indirect positive effect, through non- linear coupling between TMs and RWMs, of feedback on the TMs or to a reduced plasma- wall interaction affecting the plasma flow rotation. Electromagnetic torque calculations show that with active feedback stabilization the TMs amplitude remains well below the locking threshold condition for a thick shell. Finally, it is suggested that active feedback stabilization of RWMs and current profile control techniques can be employed simultaneously thus improving both the plasma duration and its confinement properties.

  • 22.
    Drake, James Robert
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Experiments on feedback control of multiple resistive wall modes comparing different active coil arrays and sensor types2006In: IAEA-F1-CN-149, 2006, p. Paper EX/P8-11-Conference paper (Refereed)
  • 23.
    Drake, James Robert
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, Per R
    KTH, Superseded Departments, Alfvén Laboratory.
    Yadikin, Dmitriy
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, Jenny-A.
    KTH, Superseded Departments, Alfvén Laboratory.
    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 pinch2004In: IAEA-CN-116, 2004, p. Paper EX/P2-20-Conference paper (Refereed)
  • 24.
    Drake, James Robert
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dimitry
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Malmberg, Jenny
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Liu, Y.
    Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch2005In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, no 7, p. 557-564Article in journal (Refereed)
    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.

  • 25.
    Frassinetti, L.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Brunsell, Per R.
    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.
    Menmuir, S.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch2007In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, no 11Article in journal (Refereed)
  • 26.
    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)
  • 27.
    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.
    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.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Cecconello, Marco
    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.
    Spontaneous QSH in the EXTRAP T2R reversed-field pinch2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, p. 579-582Conference paper (Refereed)
  • 28.
    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.
    Brunsell, Per 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.
    Cecconello, Marco
    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.
    Heat transport modelling in EXTRAP T2R2009In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 49, no 2Article in journal (Refereed)
    Abstract [en]

    A model to estimate the heat transport in the EXTRAP T2R reversed field pinch (RFP) is described. The model, based on experimental and theoretical results, divides the RFP electron heat diffusivity chi(e) into three regions, one in the plasma core, where chi(e) is assumed to be determined by the tearing modes, one located around the reversal radius, where chi(e) is assumed not dependent on the magnetic fluctuations and one in the extreme edge, where high chi(e) is assumed. The absolute values of the core and of the reversal chi(e) are determined by simulating the electron temperature and the soft x-ray and by comparing the simulated signals with the experimental ones. The model is used to estimate the heat diffusivity and the energy confinement time during the flat top of standard plasmas, of deep F plasmas and of plasmas obtained with the intelligent shell.

  • 29. Gregoratto, D.
    et al.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Yadikin, D.
    Liu, Y. Q.
    Paccagnella, R.
    Brunsell, Per R.
    Bolzonella, T.
    Marchiori, G.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Studies on the response of resistive-wall modes to applied magnetic perturbations in the EXTRAP T2R reversed field pinch2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 9Article in journal (Refereed)
  • 30. Hokin, S
    et al.
    Bergsåker, Henric
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, Per
    KTH, Superseded Departments, Alfvén Laboratory.
    Brzozowski, Jerzy
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Drake, James Robert
    KTH, Superseded Departments, Alfvén Laboratory.
    Hedin, G
    Hedqvist, A
    Larsson, D
    Möller, A
    Sallander, Eva
    KTH, Superseded Departments, Alfvén Laboratory.
    Sätherblom, Hans-Erik
    KTH, Superseded Departments, Alfvén Laboratory.
    Locked modes and plasma-wall interaction in a reversed-field pinch with aresistive shell and carbon first wall1999In: Proceedings of the 17th International Conference on Fusion Energy, Vienna: International Atomic Energy Agency , 1999Conference paper (Other academic)
  • 31. Ingesson, L. C.
    et al.
    Campbell, D. J.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ciattaglia, E.
    Dirken, P.
    Hawkes, N.
    Walsh, M.
    von Hellermann, M.
    Kalvin, S.
    McCarthy, P.
    Neubauer, O.
    Petrizzi, L.
    Progress on common aspects of the EU-supplied ITER diagnostics and prediction of diagnostic performance2006In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 77, no 10, p. 10F502-Article in journal (Refereed)
    Abstract [en]

    The European Union will supply a number of diagnostics for ITER. Significant progress has been made on the design and integration of these diagnostics. Specific topics, in common for several of the diagnostics, discussed are port-plug integration, simplification of labyrinths against neutron streaming, and design measures to protect and to be able to replace sensitive optical components. Performance analysis to predict the likely capability of the diagnostics to meet the ITER measurement requirements will be an important aspect of the design process. The interpretation of the measurement requirements, specifically of spatial resolution in the case of indirect measurements, is discussed on the basis of two examples, and methods of performance analysis are compared.

  • 32. Kiptily, V. G.
    et al.
    Borba, D.
    Cecil, F. E.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Darrow, D.
    Goloborod'Ko, V.
    Hill, K.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Murari, A.
    Nabais, F.
    Pinches, S. D.
    Reich, M.
    Sharapov, S. E.
    Yavorskij, V.
    Chugunov, I. N.
    Gin, D. B.
    Gorini, G.
    Shevelev, A. E.
    Syme, D. B.
    Zoita, V.
    Fast ion JET diagnostics: Confinement and losses2008In: BURNING PLASMA DIAGNOSTICS, 2008, Vol. 988, p. 283-290Conference paper (Refereed)
    Abstract [en]

    A study of magnetically confined fast ions in tokamaks plays an important role in burning plasma research. To reach ignition and steady burning of a reactor plasma an adequate confinement of energetic ions produced by NBI heating, accelerated with ICRF and born in fusion reactions is essential to provide efficient heating of the bulk plasma. Thus, investigation of the fast ion behaviour is an immediate task for present-day large machines, such as JET, in order to understand the main mechanisms of slowing down, redistribution and losses, and to develop optimal plasma scenarios. Today's JET has an enhanced suite of fast ion diagnostics both of confined and lost ions that enable to significantly contribute to this important area of research. Fast ion populations of p, d, t, 3He and 4He, made with ICRF, NBI, and fusion reactions have been investigated in experiments on JET with sophisticated diagnostics in conventional and shear-reversed plasmas, exploring a wide range of effects. This paper will introduce to the JET fast-ion diagnostic techniques and will give an overview of recent observations. A synergy of the unique diagnostic set was utilised in JET, and studies of the response of fast ions to MHD modes (e.g. tornado modes, sawtooth crashes), fast 3He-ions behaviour in shear-reversed plasmas are impressive examples of that. Some results on fast ion losses in JET experiments with various levels of the toroidal field ripple will be demonstrated.

  • 33.
    Kuldkepp, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Dux, R.
    Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Measurements and modeling of transport and impurity radial profiles in the EXTRAP T2R reversed field pinch2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 9, p. 092506-Article in journal (Refereed)
    Abstract [en]

    Radial impurity profiles of oxygen in the rebuilt reversed field pinch EXTRAP T2R [P. R. Brunsell , Plasma Phys. Control. Fusion 43, 1457 (2001)] have been measured with a multichannel spectrometer. Absolute ion densities for oxygen peak between 1-4x10(10) cm(-3) for a central electron density of 1x10(13) cm(-3). Transport simulations with the one-dimensional transport code STRAHL with a diffusion coefficient of 20 m(2) s(-1) yield density profiles similar to those measured. Direct measurement of the ion profile evolution during pulsed poloidal current drive suggests that the diffusion coefficient is reduced by a factor similar to 2 in the core but remains unaffected toward the edge. Core transport is not significantly affected by the radial magnetic field growth seen at the edge in discharges without feedback control. This indicates that the mode core amplitude remains the same while the mode eigenfunction increases at the edge.

  • 34.
    Kuldkepp, Mattias
    et al.
    KTH, Superseded Departments, Physics.
    Gravestijn, Robert
    KTH, Superseded Departments, Physics.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Rachlew, E.lisabeth
    KTH, Superseded Departments, Physics.
    A Spectroscopic Method To Determine Changes In The Temperature Profile2003In: 30th EPS Conference on Contr. Fusion and Plasma Phys / [ed] R. Koch, S. Lebedev, Mulhouse: European Physical Society , 2003Conference paper (Refereed)
  • 35.
    Kuldkepp, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    First Results The Radial 5-Channel Spectrometer On EXTRAP T2RManuscript (preprint) (Other academic)
  • 36.
    Kuldkepp, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Corre, Yann
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Oxygen impurity profile studies in the EXTRAP T2R reversed field pinch2005In: 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, p. 413-416Conference paper (Refereed)
  • 37.
    Malmberg, Jenny A.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Brzozowski, Jerzy H.
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, Per R.
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Drake, James R.
    KTH, Superseded Departments, Alfvén Laboratory.
    Mode- and plasma rotation in a resistive shell reversed-field pinch2004In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 11, no 2, p. 647-658Article in journal (Refereed)
    Abstract [en]

    Mode rotation studies in a resistive shell reversed-field pinch, EXTRAP T2R [P. R. Brunsell , Plasma Phys. Control. Fusion 43, 1 (2001)] are presented. The phase relations and nonlinear coupling of the resonant modes are characterized and compared with that expected from modeling based on the hypothesis that mode dynamics can be described by a quasi stationary force balance including electromagnetic and viscous forces. Both m=0 and m=1 resonant modes are studied. The m=1 modes have rotation velocities corresponding to the plasma flow velocity (20-60 km/s) in the core region. The rotation velocity decreases towards the end of the discharge, although the plasma flow velocity does not decrease. A rotating phase locked m=1 structure is observed with a velocity of about 60 km/s. The m=0 modes accelerate throughout the discharges and reach velocities as high as 150-250 km/s. The observed m=0 phase locking is consistent with theory for certain conditions, but there are several conditions when the dynamics are not described. This is not unexpected because the assumption of quasi stationarity for the mode spectra is not fulfilled for many conditions. Localized m=0 perturbations are formed in correlation with highly transient discrete dynamo events. These perturbations form at the location of the m=1 phase locked structure, but rotate with a different velocity as they spread out in the toroidal direction. (C) 2004 American Institute of Physics.

  • 38.
    Menmuir, Sheena
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Brunsell, Per
    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), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Ion and mode rotation in the EXTRAP T2R device during discharges with and without the application of feedback control2005Conference paper (Refereed)
  • 39. Regnoli, G.
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tennfors, E.
    Zonca, F.
    Martines, E.
    Serianni, G.
    Spolaore, M.
    Vianello, N.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Antoni, V.
    Cavazzana, R.
    Malmberg, J. A.
    Observations of toroidicity-induced Alfven eigenmodes in a reversed field pinch plasma2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 4Article in journal (Refereed)
    Abstract [en]

    High frequency peaks in the spectra of magnetic field signals have been detected at the edge of Extrap-T2R [P. R. Brunsell, H. Bergshker, M. Cecconello, J. R. Drake, R. M. Gravestijn, A. Hedqvist, and J-A. Malmberg, Plasma Phys. Controlled Fusion, 43, 1457 (2001)]. The measured fluctuation is found to be mainly polarized along the toroidal direction, with high toroidal periodicity n and Alfvenic scaling (f proportional to B / root m(i)n(i)). Calculations for, a reversed field pinch plasma predict the existence of an edge resonant, high frequency, high-n number toroidicity-induced Alfven eigenmode with the,observed frequency scaling. In addition, gas puffing experiments show that edge density fluctuations are responsible for the rapid. changes of mode frequency. Finally a coupling with the electron drift turbulence is proposed as drive mechanism for the eigenmode.

  • 40.
    Rubel, Marek J.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory.
    Malmberg, J. A.
    Sergienko, G.
    Biel, W.
    Drake, James R.
    KTH, Superseded Departments, Alfvén Laboratory.
    Hedqvist, A.
    Huber, A.
    Philipps, V.
    Dust particles in controlled fusion devices: morphology, observations in the plasma and influence on the plasma performance2001In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 41, no 8, p. 1087-1099Article in journal (Refereed)
  • 41. Schlatter, C
    et al.
    Testa, D
    Cecconello, Marco
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Murari, A
    Santala, M
    Error estimation and parameter dependence of the calculation of the fast ion distribution function, temperature, and density using data from the KF1 high energy neutral particle analyzer on Joint European Torus2004In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 75, no 10, p. 3547-3549Article in journal (Refereed)
    Abstract [en]

    Joint European Torus high energy neutral particle analyzer measures the flux of fast neutrals originating from the plasma core. From this data, the fast ion distribution function f(i)(fast), temperature T-i,perpendicular to(fast), and density n(i)(fast) are derived using knowledge of various plasma parameters and of the cross section for the required atomic processes. In this article, a systematic sensitivity study of the effect of uncertainties in these quantities on the evaluation of the neutral particle analyzer f(i)(fast), T-i,perpendicular to(fast), and n(i)(fast) is reported. The dominant parameter affecting n(i)(fast) is the impurity confinement time and therefore a reasonable estimate of this quantity is necessary to reduce the uncertainties in n(i)(fast) below 50%. On the other hand, T-i,perpendicular to(fast) is much less sensitive and can certainly be provided with an accuracy of better than 10%.

  • 42. Testa, D.
    et al.
    Cecconello, Marco
    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.
    Schlatter, C.
    The dependence of the proton-triton thermo-nuclear fusion reaction rate on the temperature and total energy content of the high-energy proton distribution function2009In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 49, no 6Article in journal (Refereed)
    Abstract [en]

    The endothermic nuclear reaction between thermal tritons and high-energy protons can represent an important contribution to the total neutron yield in tokamak plasmas heated by radio-frequency waves, as the first JET experiments have demonstrated (see Mantsinen et al 2001 Nucl. Fusion 41 1815). A further study based on more recent JET experiments was reported in Santala et al 2006 (Plasma Phys. Control. Fusion 48 1233). In this letter we supplement and complete the previous analysis by reporting the first systematic measurement of the scaling of the proton-triton (pT) thermo-nuclear fusion reaction rate as a function of the total energy content and perpendicular tail temperature of the fast protons heated by radio-frequency waves. It is found that the pT-neutron rate increases almost linearly with the fast proton temperature and the total energy content.

  • 43. Vianello, N.
    et al.
    Antoni, V.
    Spada, E.
    Spolaore, M.
    Serianni, G.
    Cavazzana, R.
    Bergsåker, Henric
    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.
    Reynolds and Maxwell stress measurements in the reversed field pinch experiment Extrap-T2R2005In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, no 8, p. 761-766Article in journal (Refereed)
  • 44. Vianello, N.
    et al.
    Antoni, V.
    Spada, E.
    Spolaore, M.
    Serianni, G.
    Cavazzana, R.
    Bergsåker, Henric
    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.
    Turbulence, flow and transport: hints from reversed field pinch2006In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, no 4, p. S193-S203Article in journal (Refereed)
  • 45. Yavorskij, V.
    et al.
    Cecconello, Marco
    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. Culham Science Centre, United Kingdom .
    Goloborod'ko, V.
    Brix, M.
    Challis, C.
    Gerasimov, S.
    Kiptily, V.
    Korotkov, A.
    Parail, V.
    Reznik, S.
    Santala, M.
    Schoepf, K.
    Sharapov, S. E.
    Surrey, E.
    De Vries, P.
    TF ripple effects on the NBI deuteron confinement in JET2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, no 2, p. 876-879Conference paper (Refereed)
    Abstract [en]

    Ripple induced reduction of the fluxes of deuterium neutrals in the 5-40 keV energy range from the plasma mid-plane was observed in recent JET experiments. The maximum observed reduction of D0 fluxes due to ripple is approximately 50 % and occurs at energies above 30 keV. In positive shear plasmas without ICRH ripple reduction of D0 fluxes vanishes at energies below 10 keV. However, in the case of plasmas with low or reversed shear core, increased D0 fluxes were observed for energies below 10-20 keV in the presence of additional ripple and ICRH heating. Interpretive modeling of the deuterium neutral emission that accounts for the superbanana ripple diffusion of NBI ions is in reasonable agreement with measurements at least for the scenarios without ICRH. Note that ripples may essentially effect the fast ion confinement in ITER where TF ripple magnitude at the outer separatrix is expected to be δ ∼ 0.5%.

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