Ändra sökning
Avgränsa sökresultatet
1 - 26 av 26
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Blanken, T. C.
    et al.
    Eindhoven Univ Technol, Control Syst Technol Grp, Dept Mech Engn, POB 513, NL-5600 MB Eindhoven, Netherlands.;Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, T.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Dori, V
    Univ Split, Fac Elect Engn Mech Engn & Naval Architecture, R Boskovica 32, Split 21000, Croatia..
    Real-time plasma state monitoring and supervisory control on TCV2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 2, artikel-id 026017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In ITER and DEMO, various control objectives related to plasma control must be simultaneously achieved by the plasma control system (PCS), in both normal operation as well as off-normal conditions. The PCS must act on off-normal events and deviations from the target scenario, since certain sequences (chains) of events can precede disruptions. It is important that these decisions are made while maintaining a coherent prioritization between the real-time control tasks to ensure high-performance operation. In this paper, a generic architecture for task-based integrated plasma control is proposed. The architecture is characterized by the separation of state estimation, event detection, decisions and task execution among different algorithms, with standardized signal interfaces. Central to the architecture are a plasma state monitor and supervisory controller. In the plasma state monitor, discrete events in the continuous-valued plasma state arc modeled using finite state machines. This provides a high-level representation of the plasma state. The supervisory controller coordinates the execution of multiple plasma control tasks by assigning task priorities, based on the finite states of the plasma and the pulse schedule. These algorithms were implemented on the TCV digital control system and integrated with actuator resource management and existing state estimation algorithms and controllers. The plasma state monitor on TCV can track a multitude of plasma events, related to plasma current, rotating and locked neoclassical tearing modes, and position displacements. In TCV experiments on simultaneous control of plasma pressure, safety factor profile and NTMs using electron cyclotron heating (ECI I) and current drive (ECCD), the supervisory controller assigns priorities to the relevant control tasks. The tasks are then executed by feedback controllers and actuator allocation management. This work forms a significant step forward in the ongoing integration of control capabilities in experiments on TCV, in support of tokamak reactor operation.

  • 2.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive Wall Mode Studies utilizing External Magnetic Perturbations2014Ingår i: Proceeding of the 25th IAEA Fusion Energy Conference, 2014, artikel-id Paper EX/P4-20Konferensbidrag (Övrigt vetenskapligt)
  • 3.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive Wall Mode Studies utilizing External Magnetic PerturbationsManuskript (preprint) (Övrigt vetenskapligt)
  • 4.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, C
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Khan, W
    Drake, J
    TM locking and unlocking mechanism to an external resonant field2014Ingår i: Meeting of the Nordic Research Units in EUROfusion, 2014Konferensbidrag (Övrigt vetenskapligt)
  • 5.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, P.R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, R
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, C
    Khan, W
    EXTEAP T2R overview2015Ingår i: 17th IEA/RFP Workshop, 26-29 october 2015, 2015Konferensbidrag (Övrigt vetenskapligt)
  • 6.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, R
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, P. R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Experimental study on the physical mechanism related to the hysteresis  of the  TM locking‐unlocking process to an external  field in EXTRAP T2R2014Ingår i: 19th workshop on MHD stability control, 2014Konferensbidrag (Övrigt vetenskapligt)
  • 7.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Men, S
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tearing mode locking and unlocking to an error field in EXTRAP T2R2013Ingår i: 18th Workshop on MHD Stability Control: Santa Fe, New Mexico, USA, 18-20 November, 2013, 2013Konferensbidrag (Övrigt vetenskapligt)
  • 8.
    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)
  • 9.
    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.

  • 10.
    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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    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.

  • 14.
    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.

  • 15.
    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)
  • 16.
    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.

  • 17.
    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)
  • 18.
    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)
  • 19.
    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)

  • 20.
    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)
  • 21.
    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.

  • 22. Joffrin, E.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Moon, Sunwoo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zhou, Yushan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zychor, I
    et al.,
    Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 11, artikel-id 112021Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.

  • 23. Saarelma, S.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bilkova, P.
    Challis, C. D.
    Chankin, A.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garzotti, L.
    Horvath, L.
    Maggi, C. F.
    Contributors, J E T
    Self-consistent pedestal prediction for JET-ILW in preparation of the DT campaign2019Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, nr 7, artikel-id 072501Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The self-consistent core-pedestal prediction model of a combination of EPED1 type pedestal prediction and a simple stiff core transport model is able to predict Type I ELMy (edge localized mode) pedestals of a large JET-ILW (ITER-like wall) database at the similar accuracy as is obtained when the experimental global plasma β is used as input. The neutral penetration model [R. J. Groebner et al., Phys. Plasmas 9, 2134 (2002)] with corrections that take into account variations due to gas fueling and plasma triangularity is able to predict the pedestal density with an average error of 15%. The prediction of the pedestal pressure in hydrogen plasma that has higher core heat diffusivity compared to a deuterium plasma with similar heating and fueling agrees with the experiment when the isotope effect on the stability, the increased diffusivity, and outward radial shift of the pedestal are included in the prediction. However, the neutral penetration model that successfully predicts the deuterium pedestal densities fails to predict the isotope effect on the pedestal density in hydrogen plasmas.

  • 24. Sweeney, R. M.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, F. A.
    Local measurement of error field using naturally rotating tearing mode dynamics in EXTRAP T2R2016Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, nr 12, artikel-id 124001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An error field (EF) detection technique using the amplitude modulation of a naturally rotating tearing mode (TM) is developed and validated in the EXTRAP T2R reversed field pinch. The technique was used to identify intrinsic EFs of m/n = 1/-12, where m and n are the poloidal and toroidal mode numbers. The effect of the EF and of a resonant magnetic perturbation (RMP) on the TM, in particular on amplitude modulation, is modeled with a first-order solution of the modified Rutherford equation. In the experiment, the TM amplitude is measured as a function of the toroidal angle as the TM rotates rapidly in the presence of an unknown EF and a known, deliberately applied RMP. The RMP amplitude is fixed while the toroidal phase is varied from one discharge to the other, completing a full toroidal scan. Using three such scans with different RMP amplitudes, the EF amplitude and phase are inferred from the phases at which the TM amplitude maximizes. The estimated EF amplitude is consistent with other estimates (e.g. based on the best EF-cancelling RMP, resulting in the fastest TM rotation). A passive variant of this technique is also presented, where no RMPs are applied, and the EF phase is deduced.

  • 25.
    Tierens, W.
    et al.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vallejos Olivares, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zuin, M.
    Consorzio RFX, Padua, Italy..
    et al.,
    Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 4, artikel-id 046001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we validate the finite element code RAPLICASOL, which models radiofrequency wave propagation in edge plasmas near ICRF antennas, against calculations with the TOPICA code. We compare the output of both codes for the ASDEX Upgrade 2-strap antenna, and for a 4-strap WEST-like antenna. Although RAPLICASOL requires considerably fewer computational resources than TOPICA, we find that the predicted quantities of experimental interest (including reflection coefficients, coupling resistances, S- and Z-matrix entries, optimal matching settings, and even radiofrequency electric fields) are in good agreement provided we are careful to use the same geometry in both codes.

  • 26.
    Trier, E.
    et al.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    ELM-induced cold pulse propagation in ASDEX Upgrade2019Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, nr 4, artikel-id 045003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In ASDEX Upgrade, the propagation of cold pulses induced by type-I edge localized modes (ELMs) is studied using electron cyclotron emission measurements, in a dataset of plasmas with moderate triangularity. It is found that the edge safety factor or the plasma current are the main determining parameters for the inward penetration of the T-e perturbations. With increasing plasma current the ELM penetration is more shallow in spite of the stronger ELMs. Estimates of the heat pulse diffusivity show that the corresponding transport is too large to be representative of the inter-ELM phase. Ergodization of the plasma edge during ELMs is a possible explanation for the observed properties of the cold pulse propagation, which is qualitatively consistent with non-linear magneto-hydro-dynamic simulations.

1 - 26 av 26
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf