Transport barrier and current profile studies on the JET Tokamak: Dissertation

    Research output: ThesisDissertationCollection of Articles

    Abstract

    One of the crucial problems in fusion research is the understanding of heat and particle transport in plasmas relevant for energy production. The neo-classical theory of tokamak transport is well-established, but it cannot explain experimental results. Instead, the micro-turbulence driven anomalous transport has been found to be dominant in present tokamak experiments. There are several mechanisms that can locally suppress micro-turbulence and reduce significantly the anomalous transport. These regions of reduced transport are called transport barriers. The presence of Internal Transport Barriers (ITBs) is one of the bases in 'Advanced Tokamak Scenarios'. One of the principal goals in the 'Advanced Tokamak Scenarios' is to improve the fusion power density and confinement with internal transport barriers by controlling the current density profile and maximising the bootstrap current - and ultimately rendering the tokamak compatible with continuous operation. This thesis reports on studies and modelling of internal transport barriers and current density profiles in the Joint European Torus (JET) tokamak with a fluid transport code. Explanations for the following open questions are sought: what are the mechanisms that govern the formation and dynamics of the ITBs in JET and secondly, how can the current density profile be modified and further, how does it affect ITBs and plasma performance? On the basis of the empirical study at the ITB transition, the wE B flow shear and magnetic shear appear as strong candidates in determining the onset time, the radial location and the dynamics of the ITBs in JET. This ITB threshold condition, employed in the semi-empirical Bohm/GyroBohm transport model, has been found to be in good agreement with experimental results in predictive transport simulations. On the other hand, the simulation results from the predictive transport modelling with a theory-based quasi-linear fluid transport model strongly emphasise the importance of the density gradient in the ITB formation. According to the current density modelling studies, lower hybrid and electron cyclotron current drive are the most versatile current drive methods in terms of the produced q-profile in the preheating phase in JET. With lower hybrid preheating, a core current hole has been found and a physics-based explanation, confirmed by the transport modelling, is given. The predictive transport simulations indicate that application of lower hybrid current drive during the high performance phase can enhance the fusion performance significantly by increasing the ITB radius.
    Original languageEnglish
    QualificationDoctor Degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Salomaa, Rainer, Supervisor, External person
    Award date7 Jun 2002
    Place of PublicationEspoo
    Publisher
    Print ISBNs951-38-5988-6
    Electronic ISBNs951-38-5989-4
    Publication statusPublished - 2002
    MoE publication typeG5 Doctoral dissertation (article)

    Fingerprint

    Joint European Torus
    profiles
    current density
    fusion
    turbulence
    heating
    simulation
    theses
    fluids
    shear flow
    cyclotrons
    radiant flux density

    Keywords

    • nuclear fusion
    • JET tokamak
    • plasma transport
    • heat transport
    • internal transport barriers
    • current density
    • modelling
    • transport models
    • flow shear
    • magnetic shear

    Cite this

    Tala, T. (2002). Transport barrier and current profile studies on the JET Tokamak: Dissertation. Espoo: VTT Technical Research Centre of Finland.
    Tala, Tuomas. / Transport barrier and current profile studies on the JET Tokamak : Dissertation. Espoo : VTT Technical Research Centre of Finland, 2002. 173 p.
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    abstract = "One of the crucial problems in fusion research is the understanding of heat and particle transport in plasmas relevant for energy production. The neo-classical theory of tokamak transport is well-established, but it cannot explain experimental results. Instead, the micro-turbulence driven anomalous transport has been found to be dominant in present tokamak experiments. There are several mechanisms that can locally suppress micro-turbulence and reduce significantly the anomalous transport. These regions of reduced transport are called transport barriers. The presence of Internal Transport Barriers (ITBs) is one of the bases in 'Advanced Tokamak Scenarios'. One of the principal goals in the 'Advanced Tokamak Scenarios' is to improve the fusion power density and confinement with internal transport barriers by controlling the current density profile and maximising the bootstrap current - and ultimately rendering the tokamak compatible with continuous operation. This thesis reports on studies and modelling of internal transport barriers and current density profiles in the Joint European Torus (JET) tokamak with a fluid transport code. Explanations for the following open questions are sought: what are the mechanisms that govern the formation and dynamics of the ITBs in JET and secondly, how can the current density profile be modified and further, how does it affect ITBs and plasma performance? On the basis of the empirical study at the ITB transition, the wE B flow shear and magnetic shear appear as strong candidates in determining the onset time, the radial location and the dynamics of the ITBs in JET. This ITB threshold condition, employed in the semi-empirical Bohm/GyroBohm transport model, has been found to be in good agreement with experimental results in predictive transport simulations. On the other hand, the simulation results from the predictive transport modelling with a theory-based quasi-linear fluid transport model strongly emphasise the importance of the density gradient in the ITB formation. According to the current density modelling studies, lower hybrid and electron cyclotron current drive are the most versatile current drive methods in terms of the produced q-profile in the preheating phase in JET. With lower hybrid preheating, a core current hole has been found and a physics-based explanation, confirmed by the transport modelling, is given. The predictive transport simulations indicate that application of lower hybrid current drive during the high performance phase can enhance the fusion performance significantly by increasing the ITB radius.",
    keywords = "nuclear fusion, JET tokamak, plasma transport, heat transport, internal transport barriers, current density, modelling, transport models, flow shear, magnetic shear",
    author = "Tuomas Tala",
    year = "2002",
    language = "English",
    isbn = "951-38-5988-6",
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    Transport barrier and current profile studies on the JET Tokamak : Dissertation. / Tala, Tuomas.

    Espoo : VTT Technical Research Centre of Finland, 2002. 173 p.

    Research output: ThesisDissertationCollection of Articles

    TY - THES

    T1 - Transport barrier and current profile studies on the JET Tokamak

    T2 - Dissertation

    AU - Tala, Tuomas

    PY - 2002

    Y1 - 2002

    N2 - One of the crucial problems in fusion research is the understanding of heat and particle transport in plasmas relevant for energy production. The neo-classical theory of tokamak transport is well-established, but it cannot explain experimental results. Instead, the micro-turbulence driven anomalous transport has been found to be dominant in present tokamak experiments. There are several mechanisms that can locally suppress micro-turbulence and reduce significantly the anomalous transport. These regions of reduced transport are called transport barriers. The presence of Internal Transport Barriers (ITBs) is one of the bases in 'Advanced Tokamak Scenarios'. One of the principal goals in the 'Advanced Tokamak Scenarios' is to improve the fusion power density and confinement with internal transport barriers by controlling the current density profile and maximising the bootstrap current - and ultimately rendering the tokamak compatible with continuous operation. This thesis reports on studies and modelling of internal transport barriers and current density profiles in the Joint European Torus (JET) tokamak with a fluid transport code. Explanations for the following open questions are sought: what are the mechanisms that govern the formation and dynamics of the ITBs in JET and secondly, how can the current density profile be modified and further, how does it affect ITBs and plasma performance? On the basis of the empirical study at the ITB transition, the wE B flow shear and magnetic shear appear as strong candidates in determining the onset time, the radial location and the dynamics of the ITBs in JET. This ITB threshold condition, employed in the semi-empirical Bohm/GyroBohm transport model, has been found to be in good agreement with experimental results in predictive transport simulations. On the other hand, the simulation results from the predictive transport modelling with a theory-based quasi-linear fluid transport model strongly emphasise the importance of the density gradient in the ITB formation. According to the current density modelling studies, lower hybrid and electron cyclotron current drive are the most versatile current drive methods in terms of the produced q-profile in the preheating phase in JET. With lower hybrid preheating, a core current hole has been found and a physics-based explanation, confirmed by the transport modelling, is given. The predictive transport simulations indicate that application of lower hybrid current drive during the high performance phase can enhance the fusion performance significantly by increasing the ITB radius.

    AB - One of the crucial problems in fusion research is the understanding of heat and particle transport in plasmas relevant for energy production. The neo-classical theory of tokamak transport is well-established, but it cannot explain experimental results. Instead, the micro-turbulence driven anomalous transport has been found to be dominant in present tokamak experiments. There are several mechanisms that can locally suppress micro-turbulence and reduce significantly the anomalous transport. These regions of reduced transport are called transport barriers. The presence of Internal Transport Barriers (ITBs) is one of the bases in 'Advanced Tokamak Scenarios'. One of the principal goals in the 'Advanced Tokamak Scenarios' is to improve the fusion power density and confinement with internal transport barriers by controlling the current density profile and maximising the bootstrap current - and ultimately rendering the tokamak compatible with continuous operation. This thesis reports on studies and modelling of internal transport barriers and current density profiles in the Joint European Torus (JET) tokamak with a fluid transport code. Explanations for the following open questions are sought: what are the mechanisms that govern the formation and dynamics of the ITBs in JET and secondly, how can the current density profile be modified and further, how does it affect ITBs and plasma performance? On the basis of the empirical study at the ITB transition, the wE B flow shear and magnetic shear appear as strong candidates in determining the onset time, the radial location and the dynamics of the ITBs in JET. This ITB threshold condition, employed in the semi-empirical Bohm/GyroBohm transport model, has been found to be in good agreement with experimental results in predictive transport simulations. On the other hand, the simulation results from the predictive transport modelling with a theory-based quasi-linear fluid transport model strongly emphasise the importance of the density gradient in the ITB formation. According to the current density modelling studies, lower hybrid and electron cyclotron current drive are the most versatile current drive methods in terms of the produced q-profile in the preheating phase in JET. With lower hybrid preheating, a core current hole has been found and a physics-based explanation, confirmed by the transport modelling, is given. The predictive transport simulations indicate that application of lower hybrid current drive during the high performance phase can enhance the fusion performance significantly by increasing the ITB radius.

    KW - nuclear fusion

    KW - JET tokamak

    KW - plasma transport

    KW - heat transport

    KW - internal transport barriers

    KW - current density

    KW - modelling

    KW - transport models

    KW - flow shear

    KW - magnetic shear

    M3 - Dissertation

    SN - 951-38-5988-6

    T3 - VTT Publications

    PB - VTT Technical Research Centre of Finland

    CY - Espoo

    ER -

    Tala T. Transport barrier and current profile studies on the JET Tokamak: Dissertation. Espoo: VTT Technical Research Centre of Finland, 2002. 173 p.