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

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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.
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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).",
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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 -