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Title: The role of zonal flows and predator–prey oscillations in triggering the formation of edge and core transport barriers

Journal Article · · Nuclear Fusion
 [1];  [1];  [1];  [2];  [1];  [3];  [3];  [4];  [4];  [5];  [6]; ;  [1];  [7];  [5];  [8];  [7];  [1]
  1. Univ. of California, Los Angeles, CA (United States)
  2. EURATOM/CCFE Fusion Assoc., Oxon (United Kingdom)
  3. General Atomics, San Diego, CA (United States)
  4. Univ. of Wisconsin, Madison, WI (United States)
  5. Univ. of California San Diego, La Jolla, CA (United States)
  6. Univ. of California San Diego, La Jolla, CA (United States); WCI Center for Fusion Theory, Daejeon (Korea)
  7. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  8. Univ. of Texas, Austin, TX (United States)
+ Show Author Affiliations

Here, we present direct evidence of low frequency, radially sheared, turbulence-driven flows (zonal flows (ZFs)) triggering edge transport barrier formation preceding the L- to H-mode transition via periodic turbulence suppression in limit-cycle oscillations (LCOs), consistent with predator–prey dynamics. The final transition to edge-localized mode-free H-mode occurs after the equilibrium E × B flow shear increases due to ion pressure profile evolution. ZFs are also observed to initiate formation of an electron internal transport barrier (ITB) at the q = 2 rational surface via local suppression of electron-scale turbulence. Multi-channel Doppler backscattering (DBS) has revealed the radial structure of the ZF-induced shear layer and the E × B shearing rate, ωE×B, in both barrier types. During edge barrier formation, the shearing rate lags the turbulence envelope during the LCO by 90°, transitioning to anti-correlation (180°) when the equilibrium shear dominates the turbulence-driven flow shear due to the increasing edge pressure gradient. The time-dependent flow shear and the turbulence envelope are anti-correlated (180° out of phase) in the electron ITB. LCOs with time-reversed evolution dynamics (transitioning from an equilibrium-flow dominated to a ZF-dominated state) have also been observed during the H–L back-transition and are potentially of interest for controlled ramp-down of the plasma stored energy and pressure (normalized to the poloidal magnetic field) $$\beta_{\theta} =2\mu_{0} n{( {T_{{\rm e}} +T_{{\rm i}}})}/{B_{\theta}^{2}}$$ in ITER.

Research Organization:
General Atomics, San Diego, CA (United States)
Sponsoring Organization:
USDOE Office of Nuclear Energy (NE)
Grant/Contract Number:
FC02-04ER54698
OSTI ID:
1352935
Journal Information:
Nuclear Fusion, Vol. 54, Issue 7; ISSN 0029-5515
Publisher:
IOP ScienceCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 32 works
Citation information provided by
Web of Science

References (33)

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Cited By (2)

A theory of self-organized zonal flow with fine radial structure in tokamak journal December 2017
Poloidal asymmetries of flows in the Tore Supra tokamak journal February 2018

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
tokamak
DIII-D
L-H transition
zonal flows
internal transport barriers
predator-prey oscillations