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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. Furthermore, the observations imply that nonlocal flux-drivenmore » mechanism may be important for the observed turbulence and electron thermal transport.« less
ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ;  [1] ;  [2] ; ORCiD logo [3] ;  [1] ;  [4] ;  [5]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. National Fusion Research Institute, Daejeon (South Korea)
  3. Univ. of California, Davis, CA (United States)
  4. Univ. of Wisconsin-Madison, Madison, WI (United States)
  5. Nova Photonics, Inc., Princeton, NJ (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1070-664X; PHPAEN
Grant/Contract Number:
AC02-76CH03073; FG03-95ER54295; FG03-99ER54518
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 11; Journal ID: ISSN 1070-664X
American Institute of Physics (AIP)
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamaks; NSTX; transport phenomena; turbulence; turbulence measurement; RF heating; electronic transport; plasma turbulence; turbulent transport processes
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1224930