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Title: Fast response of electron-scale turbulence to auxiliary heating cessation in National Spherical Torus Experiment

In this letter, we report the first observation of the fast response of electron-scale turbulence to auxiliary heating cessation in National Spherical Torus eXperiment [Ono et al., Nucl. Fusion 40, 557 (2000)]. The observation was made in a set of RF-heated L-mode plasmas with toroidal magnetic field of 0.55 T and plasma current of 300 kA. It is observed that electron-scale turbulence spectral power (measured with a high-k collective microwave scattering system) decreases significantly following fast cessation of RF heating that occurs in less than 200 μs. The large drop in the turbulence spectral power has a short time delay of about 1–2 ms relative to the RF cessation and happens on a time scale of 0.5–1 ms, much smaller than the energy confinement time of about 10 ms. Power balance analysis shows a factor of about 2 decrease in electron thermal diffusivity after the sudden drop of turbulence spectral power. Measured small changes in equilibrium profiles across the RF cessation are unlikely able to explain this sudden reduction in the measured turbulence and decrease in electron thermal transport, supported by local linear stability analysis and both local and global nonlinear gyrokinetic simulations. The observations imply that nonlocal flux-driven mechanism may be important for the observedmore » turbulence and electron thermal transport.« less
Authors:
; ; ; ; ; ; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
  2. National Fusion Research Institute, Daejeon 305-806 (Korea, Republic of)
  3. University of California at Davis, Davis, California 95616 (United States)
  4. University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
  5. Nova Photonics, Inc., Princeton, New Jersey 08540 (United States)
Publication Date:
OSTI Identifier:
22489815
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 11; 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; AUXILIARY HEATING; COMPUTERIZED SIMULATION; CONFINEMENT TIME; ELECTRIC CURRENTS; ELECTRONS; L-MODE PLASMA CONFINEMENT; MAGNETIC FIELDS; MICROWAVE RADIATION; NONLINEAR PROBLEMS; NSTX DEVICE; PLASMA; RF SYSTEMS; SPHERICAL CONFIGURATION; THERMAL DIFFUSIVITY; TIME DELAY; TOROIDAL CONFIGURATION; TURBULENCE