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Title: Linking the micro and macro: L-H transition dynamics and threshold physics

The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions. Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by anmore » increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4]
  1. CASS and Department of Physics, University of California, San Diego, California 92093 (United States)
  2. JAEA, Kashiwa (Japan)
  3. Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139 (United States)
  4. Center for Momentum Transport and Flow Organization, University of California, San Diego, California 92093 (United States)
Publication Date:
OSTI Identifier:
22408207
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 3; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DAMPING; ELECTRIC FIELDS; ELECTRON TEMPERATURE; ELECTRON-ION COUPLING; EXCITATION; HEAT FLUX; HEAT TRANSFER; HEATING; H-MODE PLASMA CONFINEMENT; ION TEMPERATURE; L-MODE PLASMA CONFINEMENT; SHEAR; TURBULENCE