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Title: Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermal diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.
Authors:
 [1] ;  [2] ;  [2] ;  [1] ;  [1] ;  [3] ;  [1] ;  [2] ;  [4] ;  [2]
  1. National Inst. for Fusion Science, Toki (Japan); Graduate Univ. for Advanced Studies, Toki (Japan)
  2. National Inst. for Fusion Science, Toki (Japan)
  3. General Atomics, San Diego, CA (United States)
  4. Kyushu Univ., Kasuga (Japan). Research Inst. for Applied Mechanics
Publication Date:
Grant/Contract Number:
FC02-04ER54698; FG03-97ER54415; AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 9; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE; National Institute for Fusion Science (NIFS-NINS)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; stochasticity; magnetic island; bifurcation; heat pulse propagation
OSTI Identifier:
1375943