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First evidence of the role of zonal flows for the L-H transition at marginal input power in the EAST tokamak.

  • Author(s): Xu, GS
  • Wan, BN
  • Wang, HQ
  • Guo, HY
  • Zhao, HL
  • Liu, AD
  • Naulin, V
  • Diamond, PH
  • Tynan, GR
  • Xu, M
  • Chen, R
  • Jiang, M
  • Liu, P
  • Yan, N
  • Zhang, W
  • Wang, L
  • Liu, SC
  • Ding, SY
  • et al.
Abstract

A quasiperiodic Er oscillation at a frequency of <4 kHz, much lower than the geodesic-acoustic-mode frequency, with a modulation in edge turbulence preceding and following the low-to-high (L-H) confinement mode transition, has been observed for the first time in the EAST tokamak, using two toroidally separated reciprocating probes. Just prior to the L-H transition, the Er oscillation often evolves into intermittent negative Er spikes. The low-frequency Er oscillation, as well as the Er spikes, is strongly correlated with the turbulence-driven Reynolds stress, thus providing first evidence of the role of the zonal flows in the L-H transition at marginal input power. These new findings not only shed light on the underlying physics mechanism for the L-H transition, but also have significant implications for ITER operations close to the L-H transition threshold power.

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