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

Journal Article · Sun Nov 15 04:00:00 EST 2015 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4935113· OSTI ID:22489815

Ren, Y.; Wang, W. X.; LeBlanc, B. P.; Guttenfelder, W.; Kaye, S. M.; Ethier, S.; Mazzucato, E.; Bell, R. ^[1]; Lee, K. C. ^[2]; Domier, C. W. ^[3]; Smith, D. R. ^[4]; Yuh, H. ^[5]

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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)

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 observed turbulence and electron thermal transport.

• OSTI ID: 22489815
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 11 Vol. 22; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

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