The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport

N. Hawkes, Y. Andrew, C. Challis, R. DeAngelis, V. Drozdov, J. Hobirk, E. Joffrin, P. Lotte, D. Mazon, E. Rachlew, S. Reyes-Cortes, F. Sattin, E. Solano, B. Stratton, Tuomas Tala, M. Valisa, Contributors to the EFDA-JET Work Programme

    Research output: Contribution to journalArticleScientificpeer-review

    26 Citations (Scopus)

    Abstract

    In JET discharges where lower hybrid heating and current drive (LHCD) is applied early during the current ramp, a region of the plasma with zero current density is formed near the axis. At the boundary of this region the current density is large and B increases rapidly over a small distance. In the central region the safety factor, q, is effectively infinite, but this falls steeply in the boundary region. Outside the boundary region q reaches a minimum, where the magnetic shear sr/q (dq/dr) becomes zero. The formation of this region of zero current is dependent on both the heating and the current drive effects of the LHCD. When LHCD is switched off the current profile begins to relax towards the resistive peaked current distribution of fully inductive tokamak operation. If LHCD is not used in the current rise then these current profiles are not established. Although the physical mechanism exists to drive the central plasma current below zero, in most cases it appears to be prevented from going negative. At least one MHD mechanism has been identified which could be responsible for this. The presence of the zero central current is closely linked to the periodic relaxation events seen in these discharges. In these discharges, internal transport barriers have been observed with additional heating powers substantially below the values required to obtain barriers in monotonic q profile cases.
    Original languageEnglish
    Pages (from-to)1105-1125
    JournalPlasma Physics and Controlled Fusion
    Volume44
    Issue number7
    DOIs
    Publication statusPublished - 2002
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    shear
    Heating
    heating
    Current density
    Plasmas
    Safety factor
    Magnetohydrodynamics
    Hot Temperature
    profiles
    current density
    safety factors
    plasma currents
    current distribution
    ramps

    Keywords

    • JET
    • plasma
    • fusion energy
    • fusion reactors
    • tokamak
    • internal transport barriers
    • lower hybrid current drive

    Cite this

    Hawkes, N., Andrew, Y., Challis, C., DeAngelis, R., Drozdov, V., Hobirk, J., ... Programme, C. T. T. EFDA-JET. W. (2002). The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport. Plasma Physics and Controlled Fusion, 44(7), 1105-1125. https://doi.org/10.1088/0741-3335/44/7/304
    Hawkes, N. ; Andrew, Y. ; Challis, C. ; DeAngelis, R. ; Drozdov, V. ; Hobirk, J. ; Joffrin, E. ; Lotte, P. ; Mazon, D. ; Rachlew, E. ; Reyes-Cortes, S. ; Sattin, F. ; Solano, E. ; Stratton, B. ; Tala, Tuomas ; Valisa, M. ; Programme, Contributors to the EFDA-JET Work. / The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport. In: Plasma Physics and Controlled Fusion. 2002 ; Vol. 44, No. 7. pp. 1105-1125.
    @article{af4b744e412e4b858e5b11ee784c486c,
    title = "The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport",
    abstract = "In JET discharges where lower hybrid heating and current drive (LHCD) is applied early during the current ramp, a region of the plasma with zero current density is formed near the axis. At the boundary of this region the current density is large and B increases rapidly over a small distance. In the central region the safety factor, q, is effectively infinite, but this falls steeply in the boundary region. Outside the boundary region q reaches a minimum, where the magnetic shear sr/q (dq/dr) becomes zero. The formation of this region of zero current is dependent on both the heating and the current drive effects of the LHCD. When LHCD is switched off the current profile begins to relax towards the resistive peaked current distribution of fully inductive tokamak operation. If LHCD is not used in the current rise then these current profiles are not established. Although the physical mechanism exists to drive the central plasma current below zero, in most cases it appears to be prevented from going negative. At least one MHD mechanism has been identified which could be responsible for this. The presence of the zero central current is closely linked to the periodic relaxation events seen in these discharges. In these discharges, internal transport barriers have been observed with additional heating powers substantially below the values required to obtain barriers in monotonic q profile cases.",
    keywords = "JET, plasma, fusion energy, fusion reactors, tokamak, internal transport barriers, lower hybrid current drive",
    author = "N. Hawkes and Y. Andrew and C. Challis and R. DeAngelis and V. Drozdov and J. Hobirk and E. Joffrin and P. Lotte and D. Mazon and E. Rachlew and S. Reyes-Cortes and F. Sattin and E. Solano and B. Stratton and Tuomas Tala and M. Valisa and Programme, {Contributors to the EFDA-JET Work}",
    note = "HUO: This paper is an extended version of a contribution to the 28th EPS Conf. on Controlled Fusion and Plasma Physics (Madeira, June 2001).",
    year = "2002",
    doi = "10.1088/0741-3335/44/7/304",
    language = "English",
    volume = "44",
    pages = "1105--1125",
    journal = "Plasma Physics and Controlled Fusion",
    issn = "0741-3335",
    publisher = "Institute of Physics IOP",
    number = "7",

    }

    Hawkes, N, Andrew, Y, Challis, C, DeAngelis, R, Drozdov, V, Hobirk, J, Joffrin, E, Lotte, P, Mazon, D, Rachlew, E, Reyes-Cortes, S, Sattin, F, Solano, E, Stratton, B, Tala, T, Valisa, M & Programme, CTTEFDA-JETW 2002, 'The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport', Plasma Physics and Controlled Fusion, vol. 44, no. 7, pp. 1105-1125. https://doi.org/10.1088/0741-3335/44/7/304

    The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport. / Hawkes, N.; Andrew, Y.; Challis, C.; DeAngelis, R.; Drozdov, V.; Hobirk, J.; Joffrin, E.; Lotte, P.; Mazon, D.; Rachlew, E.; Reyes-Cortes, S.; Sattin, F.; Solano, E.; Stratton, B.; Tala, Tuomas; Valisa, M.; Programme, Contributors to the EFDA-JET Work.

    In: Plasma Physics and Controlled Fusion, Vol. 44, No. 7, 2002, p. 1105-1125.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport

    AU - Hawkes, N.

    AU - Andrew, Y.

    AU - Challis, C.

    AU - DeAngelis, R.

    AU - Drozdov, V.

    AU - Hobirk, J.

    AU - Joffrin, E.

    AU - Lotte, P.

    AU - Mazon, D.

    AU - Rachlew, E.

    AU - Reyes-Cortes, S.

    AU - Sattin, F.

    AU - Solano, E.

    AU - Stratton, B.

    AU - Tala, Tuomas

    AU - Valisa, M.

    AU - Programme, Contributors to the EFDA-JET Work

    N1 - HUO: This paper is an extended version of a contribution to the 28th EPS Conf. on Controlled Fusion and Plasma Physics (Madeira, June 2001).

    PY - 2002

    Y1 - 2002

    N2 - In JET discharges where lower hybrid heating and current drive (LHCD) is applied early during the current ramp, a region of the plasma with zero current density is formed near the axis. At the boundary of this region the current density is large and B increases rapidly over a small distance. In the central region the safety factor, q, is effectively infinite, but this falls steeply in the boundary region. Outside the boundary region q reaches a minimum, where the magnetic shear sr/q (dq/dr) becomes zero. The formation of this region of zero current is dependent on both the heating and the current drive effects of the LHCD. When LHCD is switched off the current profile begins to relax towards the resistive peaked current distribution of fully inductive tokamak operation. If LHCD is not used in the current rise then these current profiles are not established. Although the physical mechanism exists to drive the central plasma current below zero, in most cases it appears to be prevented from going negative. At least one MHD mechanism has been identified which could be responsible for this. The presence of the zero central current is closely linked to the periodic relaxation events seen in these discharges. In these discharges, internal transport barriers have been observed with additional heating powers substantially below the values required to obtain barriers in monotonic q profile cases.

    AB - In JET discharges where lower hybrid heating and current drive (LHCD) is applied early during the current ramp, a region of the plasma with zero current density is formed near the axis. At the boundary of this region the current density is large and B increases rapidly over a small distance. In the central region the safety factor, q, is effectively infinite, but this falls steeply in the boundary region. Outside the boundary region q reaches a minimum, where the magnetic shear sr/q (dq/dr) becomes zero. The formation of this region of zero current is dependent on both the heating and the current drive effects of the LHCD. When LHCD is switched off the current profile begins to relax towards the resistive peaked current distribution of fully inductive tokamak operation. If LHCD is not used in the current rise then these current profiles are not established. Although the physical mechanism exists to drive the central plasma current below zero, in most cases it appears to be prevented from going negative. At least one MHD mechanism has been identified which could be responsible for this. The presence of the zero central current is closely linked to the periodic relaxation events seen in these discharges. In these discharges, internal transport barriers have been observed with additional heating powers substantially below the values required to obtain barriers in monotonic q profile cases.

    KW - JET

    KW - plasma

    KW - fusion energy

    KW - fusion reactors

    KW - tokamak

    KW - internal transport barriers

    KW - lower hybrid current drive

    U2 - 10.1088/0741-3335/44/7/304

    DO - 10.1088/0741-3335/44/7/304

    M3 - Article

    VL - 44

    SP - 1105

    EP - 1125

    JO - Plasma Physics and Controlled Fusion

    JF - Plasma Physics and Controlled Fusion

    SN - 0741-3335

    IS - 7

    ER -