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  • 201.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, S
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Braking torque due to external perturbations in EXTRAP T2R2013Ingår i: Joint 19th ISHW and 16th IEA-RFP workshop: Padova, Italy, 16-20 September, 2013, 2013Konferensbidrag (Refereegranskat)
  • 202.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    The tearing mode locking-unlocking mechanism to an external resonant field in EXTRAP T2R2014Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, nr 10, s. 104001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The tearing mode (TM) locking and unlocking process due to an external resonant magnetic perturbation (RMP) is experimentally studied in EXTRAP T2R. The RMP produces a reduction of the natural TM velocity and ultimately the TM locking if a threshold in the RMP amplitude is exceeded. During the braking process, the TM slows down via a mechanism composed of deceleration and acceleration phases. During the acceleration phases, the TM can reach velocities higher than the natural velocity. Once the TM locking occurs, the RMP must be reduced to a small amplitude to obtain the TM unlocking, showing that the unlocking threshold is significantly smaller than the locking threshold and that the process is characterized by hysteresis. Experimental results are in qualitative agreement with a model that describes the locking-unlocking process via the balance of the electromagnetic torque produced by the RMP that acts to brake the TM and the viscous torque that tends to re-establish the unperturbed velocity.

  • 203.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Drake, James
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    A Technique for the Estimation of the Wall Diffusion Time2012Ingår i: 54th Meeting of the APS Division of Plasma Physics, November 2012,  Providence, USA, 2012Konferensbidrag (Refereegranskat)
    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.

  • 204.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Izzo, V.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Screening effect of plasma flow on resonant magnetic perturbations in EXTRAP T2R2012Ingår i: EPS Conf. Plasma Phys., EPS Int. Congr. Plasma Phys., 2012, s. 365-368Konferensbidrag (Refereegranskat)
  • 205.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Joffrin, E.
    Tamain, P.
    Maget, P.
    Saarelma, S.
    Boom, J. E.
    Flanagan, J.
    Giroud, C.
    Delabie, E.
    Kempenaars, M.
    Lomas, P.
    Maggi, C.
    Menes, L.
    Nunes, I.
    Effect of the divertor geometry on the pedestal confinement in JET-ILW2014Ingår i: 41st EPS Conference on Plasma Physics, EPS 2014, 2014Konferensbidrag (Refereegranskat)
  • 206.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Maggi, C
    Dependence of pedestal structure and stability on beta and comparison with power/gas scans2016Ingår i: EUROfusion Science Meeting on Pedestal Studies, Sept 15, 2016, 2016Konferensbidrag (Övrigt vetenskapligt)
  • 207.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resonant magnetic perturbation penetration and locking threshold in EXTRAP T2R2013Ingår i: 40th EPS Conference on Plasma Physics: Espoo, Finland, 1-5 July, 2013, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In a tokamak or reversed field pinch plasma with rotating tearing modes (TM), the penetration of resonant magnetic perturbations (RMPs) and/or error-fields can lead to braking of the TM rotation velocity and eventually to wall locking of the TM. The TM rotation braking may occur via the electromagnetic torque that acts locally near the rational surface [1, 2, 3]. At a critical RMP amplitude, a transition from a fast rotating TM to a slowly rotating or wall locked TM occurs. This critical RMP amplitude is referred to as the error-field penetration threshold or the TM locking threshold. In this work, the threshold is experimentally studied in the EXTRAP T2R reversed-field pinch. The experimental results are compared with a model for the non-linear TM dynamics, which incorporates the balance between the electromagnetic braking torque and the viscous drag of the rotating plasma [3].

  • 208.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Khan, Waqas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    The effect of external control fields on tearing mode dynamics2011Ingår i: Proceedings of the 38th European Physical Society Conference on Plasma Physics, 2011, s. 1220-1223Konferensbidrag (Refereegranskat)
  • 209.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tearing mode velocity braking due to resonant magnetic perturbations2012Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 52, nr 10, s. 103014-Artikel i tidskrift (Refereegranskat)
    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.

  • 210.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, E
    Brunsell, P
    Menmuir, S
    Drake, J
    Screening Effect of Plasma Flow on RMP Penetration in EXTRAP T2R2011Ingår i: 53rd Meeting of the APS Division of Plasma Physics, November 2011,  Salt Lake City, USA, 2011Konferensbidrag (Refereegranskat)
  • 211.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, E
    KTH, Skolan för elektro- och systemteknik (EES).
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES).
    Drake, J
    KTH, Skolan för elektro- och systemteknik (EES).
    EXTRAP Coils and Tearing Mode Dynamics2011Ingår i: 16th Workshop on MHD stability control, November 20 - 22, 2011 San Diego, CA, USA, 2011Konferensbidrag (Övrigt vetenskapligt)
  • 212.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Olofsson, Erik
    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.
    Implementation of advanced feedback control algorithms for controlled resonant magnetic perturbation physics studies on EXTRAP T2R2011Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 51, nr 6, s. 063018-Artikel i tidskrift (Refereegranskat)
    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.

  • 213.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resonant magnetic perturbation effect on tearing mode dynamics2010Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 3, s. 035005-Artikel i tidskrift (Refereegranskat)
    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.

  • 214.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Khan, Muhammad Waqas Mehmood
    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 R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Controlled Resonant Magnetic Perturbation Physics Studies on EXTRAP T2R2010Ingår i: Proc. 23 rd IAEA Fusion Energy Conference, IAEA , 2010Konferensbidrag (Refereegranskat)
  • 215.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, F. A.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    A method for the estimate of the wall diffusion for non-axisymmetric fields using rotating external fields2013Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, nr 8, s. 084001-Artikel i tidskrift (Refereegranskat)
    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.

  • 216.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik. J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Khan, Muhammad Waqas Mehmood
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Experimental Studies of the Plasma Response to Applied Nonaxisymmetric External Magnetic Perturbations in EXTRAP T2R2012Ingår i: 24th IAEA Fusion Energy Conference, 2012, s. EX/P4-21-Konferensbidrag (Refereegranskat)
  • 217.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Saarelma, S.
    Imbeaux, F.
    Verdoolaege, G.
    Bilkova, P.
    Bohm, P.
    Fridström, R.
    Giovannozzi, E.
    Owsiak, M.
    Dunne, M.
    Labit, B.
    Scannell, R.
    Hillesheim, J. C.
    The EUROfusion JET-ILW pedestal database2018Ingår i: 45th EPS Conference on Plasma Physics, EPS 2018, European Physical Society (EPS) , 2018, s. 1056-1059Konferensbidrag (Refereegranskat)
  • 218.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Saarelma, S
    Lomas, P
    Nunes, I
    Beurskens, M
    Dimensionless scans in low δ baseline JET-ILW plasmas and comparison with JET-C2016Ingår i: 43rd European Physical Society Conference on Plasma Physics, EPS 2016, 2016Konferensbidrag (Refereegranskat)
  • 219.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Saarelma, S.
    Lomas, P.
    Nunes, I.
    Rimini, F.
    Beurskens, M. N. A.
    Bilkova, P.
    Boom, J. E.
    de la Luna, E.
    Delabie, E.
    Drewelow, P.
    Flanagan, J.
    Garzotti, L.
    Giroud, C.
    Hawks, N.
    Joffrin, E.
    Kempenaars, M.
    Kim, Hyun-Tae
    Kruezi, U.
    Loarte, A.
    Lomanowski, B.
    Lupelli, I.
    Meneses, L.
    Maggi, C. F.
    Menmuir, S.
    Peterka, M.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Romanelli, M.
    Stefanikova, E.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Dimensionless scalings of confinement, heat transport and pedestal stability in JET-ILW and comparison with JET-C2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 1, artikel-id 014014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three dimensionless scans in the normalized Larmor radius rho*, normalized collisionality nu* and normalized plasma pressure beta have been performed in JET with the ITER-like wall (JET-ILW). The normalized energy confinement and the thermal diffusivity exhibit a scaling with rho* consistent with the earlier results obtained in the carbon wall JET (JET-C) and with a gyro-Bohm scaling. In the pedestal, experimental results show that the stability is not dependent on rho*, qualitatively in agreement with the peeling-ballooning (P-B) model. The nu* dimensionless scaling shows that JET-ILW normalized confinement has a stronger dependence on collisionality than JET-C. This leads to a reduction of the difference in the confinement between JET-ILW and JET-C to approximate to 10% at low nu*. The pedestal stability shows an improvement with decreasing nu*. This is ascribed to the increase of the bootstrap current, to the reduction of the pedestal width and to the reduction of the relative shift between pedestal density and temperature position. The beta dimensionless scan shows that, at low collisionality, JET-ILW normalized confinement has no clear dependence with beta, in agreement with part of the earlier scalings. At high collisionality, a reduction of the normalized confinement with increasing beta is observed. This behaviour is driven mainly by the pedestal where the stability is reduced with increasing beta. The P-B analysis shows that the stability reduction with increasing beta at high nu* is due to the destabilizing effect of the increased relative shift.

  • 220.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vektoranalys2019 (uppl. 1)Bok (Refereegranskat)
    Abstract [sv]

    Läroböcker i vektoranalys är ofta kortfattade. Denna bok, som kan användas för såväl grundläggande som mer avancerade kurser, behandlar ämnet mer utförligt.

    Bokens pedagogiska idé skiljer sig markant från liknande böcker. Återkommande inslag är tydligt formulerade problem som fångar det centrala i vektoranalysen. Syftet med problemen är dels att väcka intresse för den teori och de metoder som behandlas, dels att stimulera till aktivt lärande. 

    Boken innehåller genomarbetade och lättillgängliga teoriavsnitt - som börjar med grundläggande vektoralgebra och slutar med kartesiska tensorer och en härledning av vektoranalysens huvudsats. Dessutom ingår ett stort antal konkreta exempel och många tillämpningar. Sist i varje kapitel finns en sammanfattning av den viktigaste teorin och övningsuppgifter med svar. Ledningar och fullständiga lösningar finns på Libers webbplats. Där finns även ett Appendix med tillämpningar.

  • 221.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, E
    Loarte, A
    Effect of relative on pedestal stability in JET-ILW and comparison with JET-C2016Ingår i: ITPA-PEP meeting, 24-26 October 2016, 2016Konferensbidrag (Övrigt vetenskapligt)
  • 222.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sun, Y.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. E. J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Khan, M. W. M.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Liang, Y.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Braking due to non-resonant magnetic perturbations and comparison with neoclassical toroidal viscosity torque in EXTRAP T2R2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 11, artikel-id 112003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The non-resonant magnetic perturbation (MP) braking is studied in the EXTRAP T2R reversed-field pinch (RFP) and the experimental braking torque is compared with the torque expected by the neoclassical toroidal viscosity (NTV) theory. The EXTRAP T2R active coils can apply magnetic perturbations with a single harmonic, either resonant or non-resonant. The non-resonant MP produces velocity braking with an experimental torque that affects a large part of the core region. The experimental torque is clearly related to the plasma displacement, consistent with a quadratic dependence as expected by the NTV theory. The work show a good qualitative agreement between the experimental torque in a RFP machine and NTV torque concerning both the torque density radial profile and the dependence on the non-resonant MP harmonic.

  • 223.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sun, Y.
    Khan, Muhammad Waqas Mehmood
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Flow braking due to non-resonant external perturbations in EXTRAP T2R and comparison   with neoclassical toroidal viscosity torque2012Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics, 2012, s. 1190-1193Konferensbidrag (Refereegranskat)
  • 224.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sun, Y
    Khan, Muhammad Waqas Mehmood
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Screening effect of plasma flow on RMPs in EXTRAP T2R2012Ingår i: 39th European Physical Society (EPS) Conference on Plasma Physics, 2012, s. P1.067-Konferensbidrag (Refereegranskat)
  • 225. Fridström, R.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Piron, L.
    Piovesan, P.
    Zaniol, B.
    Brunsell, P.
    Plasma flow braking due to non-resonant and resonant magnetic perturbations in RFX-mod2013Ingår i: Joint 19th ISHW and 16th IEA-RFP workshop, Sept 2013, Padova, Italy, 2013Konferensbidrag (Övrigt vetenskapligt)
  • 226. Fridström, R
    et al.
    Munaretto, S
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, B
    Brunsell, P.R.
    Sarff, J
    Measuring viscosity with a resonant magnetic perturbation in the MST RFP2016Ingår i: 21th workshop on MHD stability control, November 2016, S.Diego, USA, 2016Konferensbidrag (Övrigt vetenskapligt)
  • 227. Fridström, R
    et al.
    Munaretto, S
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, B
    Brunsell, P.R.
    Sarff, J
    Measuring viscosity with a resonant magnetic perturbation in the MST RFP2016Ingår i: 58th Annual Meeting of the APS Division of Plasma Physics, 31-oct / 4Nov 2016 San Jose, California, 2016Konferensbidrag (Övrigt vetenskapligt)
  • 228.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resonant magnetic perturbation effect on the tearing mode dynamics: Novel measurements and modeling of magnetic fluctuation induced momentum transport in the reversed-field pinch2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode.

    In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity.

    In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science.

  • 229.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tearing mode dynamics in the presence of resonant magnetic perturbations2016Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Magnetically confined fusion (MCF) plasmas are typically subject to several unstable modes. The growth of one mode can limit the plasma energy confinement and might cause a termination of the plasma. Externally applied resonant magnetic perturbations (RMPs) are used to control and to mitigate some of the unstable modes. Examples are, mitigation of edge localized modes and steering of neoclassical tearing mode position for stabilization by electron cyclotron current drive. Consequently, use of RMPs are considered necessary in planned future fusion machines. There are however negative consequences, the RMP interaction with a tearing mode (TM) of the same resonance can cause deceleration of the TM and possibly wall-locking. If a TM is non-rotating relative the machine-wall, it can grow and degrade fusion plasma performance and lead to a plasma disruption. Thus, all fusion confinement machines want to avoid wall-locked modes. Resonant magnetic fields can also be present in the form of machine-error-fields, which can produce the same effects. Clearly, it is of importance to understand the TM-RMP interaction. Typically, the modes with long wavelength are described by magnetohydrodynamic (MHD) theory. Considering the finite plasma resistivity, MHD predicts a mode that tears and reconnects magnetic field lines, called a tearing mode (TM). TMs occur at surfaces where the magnetic field lines close on themselves after a number of (m) toroidal and (n)poloidal turns. These surfaces are resonant in the sense that magnetic field and helical current perturbation has the same helicity, which minimize stabilizing effect of magnetic field line bending. In this thesis, the mechanisms of TM locking and unlocking due to external resonant magnetic perturbations (RMPs) are experimentally studied. The studies are conducted in two MCF machines of the type reversed-field pinch (RFP): EXTRAP T2R and Madison Symmetric Torus (MST). The studied machines exhibit multiple rotating TMs under normal operation. In EXTRAP T2R TM locking and unlocking are studied by application of a single harmonic RMP. Observations show that after the TM is locked, RMP amplitude has to be reduced significantly in order to unlock the TM. In similar studies in MST unlocking is not observed at all after turn-off of the RMP. Hence, in both machines, there is hysteresis in the locking and subsequent unlocking of a tearing mode. Results show qualitative agreement with a theoretical model of the TM evolution when subjected to an RMP. It is shown that the RMP cause a reduction of TM and plasma rotation at the resonant surface. The velocity reduction is opposed by a viscous torque from surrounding plasma. After TM locking, relaxation of the whole plasma rotation is observed, due to the transfer of velocity reduction via viscosity. This results in a reduced viscous resorting torque, which explains the observed hysteresis. The hysteresis is further deepened by the increase in amplitude of a locked mode.

  • 230.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Multiple-harmonics RMP effect on tearing modes in EXTRAP T2R2017Konferensbidrag (Övrigt vetenskapligt)
  • 231.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, B. E.
    Univ Wisconsin, Dept Phys, 1150 Univ Ave, Madison, WI 53706 USA..
    Almagri, A. F.
    Univ Wisconsin, Dept Phys, 1150 Univ Ave, Madison, WI 53706 USA..
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Nishizawa, T.
    Univ Wisconsin, Dept Phys, 1150 Univ Ave, Madison, WI 53706 USA..
    Sarff, J. S.
    Univ Wisconsin, Dept Phys, 1150 Univ Ave, Madison, WI 53706 USA..
    Dependence of Perpendicular Viscosity on Magnetic Fluctuations in a Stochastic Topology2018Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, nr 22, artikel-id 225002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In a magnetically confined plasma with a stochastic magnetic field, the dependence of the perpendicular viscosity on the magnetic fluctuation amplitude is measured for the first time. With a controlled, similar to tenfold variation in the fluctuation amplitude, the viscosity increases similar to 100-fold, exhibiting the same fluctuation-amplitude-squared dependence as the predicted rate of stochastic field line diffusion. The absolute value of the viscosity is well predicted by a model based on momentum transport in a stochastic field, the first in-depth test of this model.

  • 232.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, Brett
    Almagri, Abdulgader
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Nishizawa, Takashi
    Sarff, John
    Dependence of perpendicular viscosity on magnetic fluctuations in a stochastic topologyManuskript (preprint) (Övrigt vetenskapligt)
  • 233.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, Brett E.
    Almagri, Abdulgader F.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Nishizawa, Takashi
    Sarff, John S.
    Modeled and measured magnetic fluctuation induced momentum transport in the reversed-field pinchManuskript (preprint) (Övrigt vetenskapligt)
  • 234.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hysteresis in the tearing mode locking/unlocking due to resonant magnetic perturbations in EXTRAP T2R2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 10, artikel-id 104008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The physical mechanisms behind the hysteresis in the tearing mode locking and unlocking to a resonant magnetic perturbation (RMP) are experimentally studied in EXTRAP T2R reversed-field pinch. The experiments show that the electromagnetic and the viscous torque increase with increasing perturbation amplitude until the mode locks to the wall. At the wall-locking, the plasma velocity reduction profile is peaked at the radius where the RMP is resonant. Thereafter, the viscous torque drops due to the relaxation of the velocity in the central plasma. This is the main reason for the hysteresis in the RMP locking and unlocking amplitude. The increased amplitude of the locked tearing mode produces further deepening of the hysteresis. Both experimental results are in qualitative agreement with the model in Fitzpatrick et al (2001 Phys. Plasmas 8 4489)

  • 235.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Munaretto, S
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, B
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sarff, J.S.
    Estimation of anomalous viscosity based on modeling of experimentally observed plasma rotation braking induced by applied resonant magnetic perturbations2016Ingår i: 43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016, European Physical Society (EPS) , 2016Konferensbidrag (Refereegranskat)
  • 236.
    Fridström, Richard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Munaretto, Stefano
    Lorenzo, Frassinetti
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Chapman, Brett E.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sarff, John
    Tearing mode dynamics and locking in the presence of external magnetic perturbations2016Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, s. 062504-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In normal operation, Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch plasmas exhibit several rotating tearing modes (TMs). Application of a resonant magnetic perturbation (RMP) results in braking of mode rotation and, if the perturbation amplitude is sufficiently high, in a wall-locked state. The coils that produce the magnetic perturbation in MST give rise to RMPs with several toroidal harmonics. As a result, simultaneous deceleration of all modes is observed. The measured TM dynamics is shown to be in qualitative agreement with a magnetohydrodynamical model of the RMP interaction with the TM [R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)] adapted to MST. To correctly model the TM dynamics, the electromagnetic torque acting on several TMs is included. Quantitative agreement of the TM slowing-down time was obtained for a kinematic viscosity in the order of ν≈10–20 m2/s. Analysis of discharges with different plasma densities shows an increase of the locking threshold with increasing density. Modeling results show good agreement with the experimental trend, assuming a density-independent kinematic viscosity. Comparison of the viscosity estimates in this paper to those made previously with other techniques in MST plasmas suggests the possibility that the RMP technique may allow for estimates of the viscosity over a broad range of plasmas in MST and other devices.

  • 237. Frigione, D.
    et al.
    Challis, C.
    Garcia, J.
    Hobirk, J.
    Alper, B.
    Artaserse, G.
    Angioni, C.
    Baruzzo, M.
    Belonohy, E.
    Bilato, R.
    Brett, A.
    Buratti, P.
    Carvallho, I.
    Casson, F.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garzotti, L.
    Giovannozzi, E.
    Grist, D.
    Hawkes, N. C.
    Lerche, E.
    Mailloux, J.
    Mantica, P.
    Maslov, M.
    Morris, J.
    Pucella, G.
    Rachlew, E.
    Reich, M.
    Rimini, F.
    Sips, A. C. C.
    Stamp, M. F.
    Tamain, P.
    Tsalas, M.
    Valisa, M.
    Weisen, H.
    Overview of hybrid development in JET with ITER-Like Wall2015Ingår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferensbidrag (Refereegranskat)
  • 238.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Impact of material migration on plasma-facing components in tokamaks2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Plasma-wall interaction plays an essential role in the performance and safety of a fusion reactor. This thesis focuses on the impact of material migration on plasma-facing components. It is based on experiments performed in tokamaks: JET, TEXTOR and ASDEX Upgrade. The objectives of the experiments were to assess fuel and impurity removal under ion cyclotron wall conditioning (ICWC) and plasma impact on diagnostic mirrors.

    In wall conditioning studies, tracer techniques based on the injection of rare isotopes (15N, 18O) were used to determine conclusively the impact of the respective gases. For the first time, probe surfaces and wall components exposed to ICWC were examined by surface analysis methods. Discharges in hydrogen were the most efficient to erode carbon co-deposits, resulting in a reduction of the initial deuterium content by a factor of two. It was also found that impurities desorbed under ICWC are partly re-deposited on the wall.

    Plasma impact on diagnostic mirrors was determined by surface analysis of test mirrors exposed at JET. Reflectivity of mirrors from the divertor region was severely decreased due to deposits of beryllium, deuterium, carbon and other impurities. This result points out the need to develop mirror maintenance procedures. Neutron damage on mirrors was simulated by ion irradiation in an ion implanter. It was shown that damage levels similar to those expected in the first wall of a fusion reactor do not produce a significant change in reflectivity.

  • 239.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Investigation of probe surfaces after ion cyclotron wall conditioning in ASDEX UpgradeManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    For the first time, material analysis techniques have been applied to study the effect of ion cyclotron wall conditioning (ICWC) on probe surfaces in a metal-wall machine. ICWC is a technique envisaged to contribute to the removal of fuel and impurities from the first wall of ITER. The objective of this work was to assess impurity migration under the ICWC operation. Tungsten probes were exposed in ASDEX Upgrade to discharges in helium. After wall conditioning, the probes were covered with a co-deposited layer containing D, B, C, N, O and relatively high amount of He on virgin W substrates. The concentration ratio He/C+B was 0.7. The formation of the co-deposited layer indicates that a fraction of the impurities desorbed from the wall under ICWC operation are transported by plasma and deposited away from their original location.

  • 240.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Plasma impact on diagnostic mirrors in JETManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    All optical diagnostics in ITER will rely on metallic mirrors acting as plasma-facing components. This contribution provides a comprehensive account on plasma impact on diagnostic mirrors in JET with the ITER-Like Wall. Specimens from the First Mirror Test and the lithium-beam diagnostic have been studied by spectrophotometry, ion beam analysis and electron microscopy. Test mirrors made of molybdenum were retrieved from the main chamber and the divertor after exposure to the 2013-2014 experimental campaign. In the main chamber, only mirrors located at the entrance of the carrier lost reflectivity (Be deposition from the eroded limiters), while those located deeper in the carrier were only slightly affected. The performance of mirrors in the JET divertor was strongly degraded by deposition of beryllium, tungsten and other species. Mirrors from the lithium-beam diagnostic have been studied for the first time. Gold coatings were severely damaged by intense arcing. As a consequence, material mixing of the gold layer with the stainless steel substrate occurred. Total reflectivity dropped from over 90% to less than 60 %, i.e. to the level typical for stainless steel.

  • 241.
    Garcia Carrasco, Alvaro
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Möller, S.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Kreter, A.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Wauters, T.
    Impact of ion cyclotron wall conditioning on fuel removal from plasma-facing components at TEXTOR2014Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014017-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ion cyclotron wall conditioning (ICWC) is based on low temperature and low density plasmas produced and sustained by ion cyclotron resonance (ICR) pulses in reactive or noble gases. The technique is being developed for ITER. It is tested in tokamaks in the presence of toroidal magnetic field (0.2-3.8 T) and heating power of the order of 10(5) W. ICWC with hydrogen, deuterium and oxygen-helium mixture was studied in the TEXTOR tokamak. The exposed samples were pre-characterized limiter tiles mounted on specially designed probes. The objectives were to assess the reduction of deuterium content, the uniformity of the reduction and the retention of seeded oxygen. For the last objective oxygen-18 was used as a marker. ICWC in hydrogen caused a drop of deuterium content in the tile by a factor of more than 2: from 4.5x10(18) to 1.9x10(18) D cm(-2). A decrease of the fuel content by approximately 25% was achieved by the ICWC in oxygen, while no reduction of the fuel content was measured after exposure to discharges in deuterium. These are the first data ever obtained showing quantitatively the local decrease of deuterium in wall components treated by ICWC in a tokamak. The oxygen retention in the tiles exposed to ICWC with oxygen-helium was analyzed for different orientations and radial positions with respect to plasma. An average retention of 1.38x10(16) O-18 cm(-2) was measured. A maximum of the retention, 4.4x10(16) O-18 cm(-2), was identified on a sample surface near the plasma edge. The correlation with the gas inlet and antennae location has been studied.

  • 242.
    Garcia Carrasco, Alvaro
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Fortuna-Zalesna, E.
    Jachmich, S.
    Brix, M.
    Marot, L.
    Plasma impact on diagnostic mirrors in JET2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 506-512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metallic mirrors will be essential components of all optical systems for plasma diagnosis in ITER. This contribution provides a comprehensive account on plasma impact on diagnostic mirrors in JET with the ITER-Like Wall. Specimens from the First Mirror Test and the lithium-beam diagnostic have been studied by spectrophotometry, ion beam analysis and electron microscopy. Test mirrors made of molybdenum were retrieved from the main chamber and the divertor after exposure to the 2013-2014 experimental campaign. In the main chamber, only mirrors located at the entrance of the carrier lost reflectivity (Be deposition), while those located deeper in the carrier were only slightly affected. The performance of mirrors in the JET divertor was strongly degraded by deposition of beryllium, tungsten and other species. Mirrors from the lithium-beam diagnostic have been studied for the first time. Gold coatings were severely damaged by intense arcing. As a consequence, material mixing of the gold layer with the stainless steel substrate occurred. Total reflectivity dropped from over 90% to less than 60%, i.e. to the level typical for stainless steel.

  • 243.
    Garcia Carrasco, Alvaro
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Schwarz-Selinger, T.
    Wauters, T.
    Douai, D.
    Bobkov, V.
    Cavazzana, R.
    Krieger, K.
    Lyssoivan, A.
    Moeller, S.
    Spolaore, M.
    Rohde, V.
    Rubel, M.
    Investigation of probe surfaces after ion cyclotron wall conditioning in ASDEX upgrade2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 733-735Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the first time, material analysis techniques have been applied to study the effect of ion cyclotron wall conditioning (ICWC) on probe surfaces in a metal-wall machine. ICWC is a technique envisaged to contribute to the removal of fuel and impurities from the first wall of ITER. The objective of this work was to assess impurity migration under ICWC operation. Tungsten probes were exposed in ASDEX Upgrade to discharges in helium. After wall conditioning, the probes were covered with a co-deposited layer containing D, B, C, N, O and relatively high amount of He. The concentration ratio He/C+B was 0.7. The formation of the co-deposited layer indicates that a fraction of the impurities desorbed from the wall under ICWC operation are transported by plasma and deposited away from their original location.

  • 244.
    Garcia Carrasco, Alvaro
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Wauters, T.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drenik, A.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Crombé, K.
    Douai, D.
    Fortuna, E.
    Kogut, D.
    Kreter, A.
    Lyssoivan, A.
    Möller, S.
    Pisarek, M.
    Vervier, M.
    Nitrogen removal from plasma-facing components by ion cyclotron wall conditioning in TEXTOR2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 688-692Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The efficiency of ion cyclotron wall conditioning (ICWC) in the removal of nitrogen from plasma-facing components in TEXTOR was assessed. In two experiments the wall was loaded with nitrogen and subsequently cleaned by ICWC in deuterium and helium. The retention and removal of nitrogen was studied in-situ by means of mass spectrometry, and ex-situ by surface analysis of a set of graphite, tungsten and TZM plates installed on test limiter systems. N-15 rare isotope was used as a marker. The results from the gas balance showed that about 25% of the retained nitrogen was removed after ICWC cleaning, whereas surface analysis of the plates based on ToF-HIERDA showed an increase of the deposited species after the cleaning. This indicates that during ICWC operation on carbon devices, nitrogen is not only pumped out but also transported to other locations on the wall. Additionally, deuterium surface content was studied before and after ICWC cleaning.

  • 245.
    Garcia-Carrasco, Alvaro
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hallén, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Grzonka, J.
    Gilbert, M. R.
    Fortuna-Zalesna, E.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Impact of helium implantation and ion-induced damage on reflectivity of molybdenum mirrors2016Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molybdenum mirrors were irradiated with Mo and He ions to simulate the effect of neutron irradiation on diagnostic first mirrors in next-generation fusion devices. Up to 30 dpa were produced under molybdenum irradiation leading to a slight decrease of reflectivity in the near infrared range. After 3×1017 cm-2 of helium irradiation, reflectivity decreased by up to 20%. Combined irradiation by helium and molybdenum led to similar effects on reflectivity as irradiation with helium alone. Ion beam analysis showed that only 7% of the implanted helium was retained in the first 40nm layer of the mirror. The structure of the near-surface layer after irradiation was studied with scanning transmission electron microscopy and the extent and size distribution of helium bubbles was documented. The consequences of ion-induced damage on the performance of diagnostic components are discussed.

  • 246.
    Garcia-Munoz, M.
    et al.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Sharapov, S. E.
    Culham Sci Ctr, Abingdon, Oxon, England..
    Van Zeeland, M. A.
    Gen Atom, San Diego, CA USA..
    Ascasibar, E.
    CIEMAT, Madrid, Spain..
    Cappa, A.
    CIEMAT, Madrid, Spain..
    Chen, L.
    Zhejiang Univ, IFTS, Hangzhou, Zhejiang, Peoples R China.;Zhejiang Univ, Dept Phys, Hangzhou, Zhejiang, Peoples R China.;Univ Calif Irvine, Dept Phys & Astron, Irvine, CA USA..
    Ferreira, J.
    IST, Lisbon, Portugal..
    Galdon-Quiroga, J.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Geiger, B.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Gonzalez-Martin, J.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Heidbrink, W. W.
    Univ Calif Irvine, Dept Phys & Astron, Irvine, CA USA..
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Lauber, Ph
    Max Planck Inst Plasma Phys, Garching, Germany..
    Mantsinen, M.
    Barcelona Supercomp Ctr, Barcelona, Spain.;ICREA, Pg Lluis Companys 23, Barcelona, Spain..
    Melnikov, A. , V
    Nabais, F.
    Univ Calif Irvine, Dept Phys & Astron, Irvine, CA USA..
    Rivero-Rodriguez, J. F.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Sanchis-Sanchez, L.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Schneider, P.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Stober, J.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Suttrop, W.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Todo, Y.
    Natl Inst Fus Sci, Toki, Gifu, Japan..
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zonca, F.
    Zhejiang Univ, IFTS, Hangzhou, Zhejiang, Peoples R China.;Zhejiang Univ, Dept Phys, Hangzhou, Zhejiang, Peoples R China.;ENEA, Fus & Nucl Safety Dept, CR Frascati, Rome, Italy..
    Meyer, H.
    Active control of Alfven eigenmodes in magnetically confined toroidal plasmas2019Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, nr 5, artikel-id 054007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alfven waves are electromagnetic perturbations inherent to magnetized plasmas that can be driven unstable by a free energy associated with gradients in the energetic particles' distribution function. The energetic particles with velocities comparable to the Alfven velocity may excite Alfven instabilities via resonant wave-particle energy and momentum exchange. Burning plasmas with large population of fusion born super-Alfvenic alpha particles in magnetically confined fusion devices are prone to excite weakly-damped Alfven eigenmodes (AEs) that, if allowed to grow unabated, can cause a degradation of fusion performance and loss of energetic ions through a secular radial transport. In order to control the fast-ion distribution and associated Alfvenic activity, the fusion community is currently searching for external actuators that can control AEs and energetic ions in the harsh environment of a fusion reactor. Most promising control techniques are based on (i) variable fast-ion sources to modify gradients in the energetic particles' distribution, (ii) localized electron cyclotron resonance heating to affect the fast-ion slowing-down distribution, (iii) localized electron cyclotron current drive to modify the equilibrium magnetic helicity and thus the AE existence criteria and damping mechanisms, and (iv) externally applied 3D perturbative fields to manipulate the fast-ion distribution and thus the wave drive. Advanced simulations help to identify the key physics mechanisms underlying the observed AE mitigation and suppression and thus to develop robust control techniques towards future burning plasmas.

  • 247.
    García Carrasco, Álvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Plasma-Facing Components in Tokamaks: Studies of Wall Conditioning Processes and Plasma Impact on Diagnostic Mirrors2014Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Understanding of material migration and its impact on the formation of co-deposited mixed material layers on plasma-facing components is essential for the development of fusion reactors. This thesis focuses on this topic. It is based on experiments performed at JET and TEXTOR tokamaks. The major objectives were to determine: (i) fuel and impurity removal from plasma-facing components by ICWC in different gas mixtures, (ii) fuel and impurity transport connected to ICWC operation, (iii) plasma impact on diagnostic mirrors. All these issues are in line with the ITER needs: mitigation of co-deposition and fuel inventory, and the performance of first mirrors in long-term operation. The novelty in research is demonstrated by several elements. In wall conditioning studies, tracer techniques based on injection of rare isotopes (N-15, O-18) were used to determine conclusively the impact of respective gases. Also, a new approach to ICWC was developed by combining global gas balance studies based on mass spectrometry and the use of multiple surface probes exposed to discharges and then studied ex-situ with accelerator-based techniques. Impact of plasma on diagnostic mirrors was determined after exposure to the entire first experimental campaign in JET-ILW.

  • 248. Gasior, P.
    et al.
    Badziak, J.
    Czarnecka, A.
    Parys, P.
    Wolowski, J.
    Rosinski, M.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Philipps, V.
    Characterization of laser-irradiated co-deposited layers on plasma facing components from a tokamak2006Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T123, s. 99-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental setup and ion diagnostic method for laser-induced fuel removal and decomposition of co-deposited layers on plasma facing components from tokamaks are described. Nd:YAG 3.5 ns pulse laser with a repetition rate of 10 Hz and single-pulse energy of up to 0.8J at 1.06 mu m has been used for irradiation of a graphite limiter tile from the TEXTOR tokamak. Comparative studies have been performed for a pure graphite plate as a reference target. Energy of emitted ions has been measured using a time-of-flight method. Early results show that laser pulses efficiently ablate the co-deposit removing both fuel species and heavy components such as Si, Ni, Cr, Fe and W present in the layers. Surface topography of the irradiated targets is also presented.

  • 249. Gasior, P.
    et al.
    Czarnecka, A.
    Parys, P.
    Rosinski, M.
    Wolowski, J.
    Hoffman, J.
    Szymanski, Z.
    Philipps, V.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Effective laser-induced removal of co-deposited layers from plasma-facing components in a tokamak2006Ingår i: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 56, s. B67-B72Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental set-up and spectroscopy diagnostic method for laser-induced fuel removal and decomposition of co-deposited layers on plasma-facing components from tokamaks are described. For irradiation of a graphite limiter tile from the TEXTOR tokamak Nd:YAG 3.5-ns pulse laser with a repetition rate of 10 Hz and single pulse energy of up to 0,8 J at 1,06 mu m has been used. The spectroscopy system allowed recording of spectra in the visible wavelength range including CII and D alpha spectral lines. The evolution of CII and Da spectral lines was observed pulse-by-pulse during the co-deposit removal. The efficient ablation of the 45 mu m thick co-deposit occured after approximately 50 laser pulses.

  • 250. Gasior, P.
    et al.
    Irrek, F.
    Petersson, P.
    Penkalla, Hj.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Schweer, B.
    Sundelin, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Wessel, E.
    Linke, J.
    Philipps, V.
    Emmoth, Birger
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Wolowski, J.
    Hirai, T.
    Laser-induced removal of co-deposits from graphitic plasma-facing components: Characterization of irradiated surfaces and dust particles2009Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 390-91, s. 585-588Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser-induced fuel desorption and ablation of co-deposited layers on limiter plates from the TEXTOR tokamak have been studied. Gas phase composition was monitored in situ, whereas the ex situ studies have been focused on the examination of irradiated surfaces and broad analysis of dust generated by ablation of co-deposits. The size of the dust grains is in the range of few nanometers to hundreds of micrometers. These are fuel-rich dust particles, as determined by nuclear reaction analysis. The presence of deuterium in dust indicates that not all fuel species are transferred to the gas phase during irradiation. This also suggests that photonic removal of fuel and the ablation of co-deposit from plasma-facing components may lead to the redistribution of fuel-containing dust to surrounding areas.

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