Study of turbulent fluctuations driven by the electron temperature gradient in the National Spherical Torus Experiment

Journal Article · Thu Jan 01 00:00:00 EST 2009 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/49/5/055001· OSTI ID:1018276

Mazzucato, E. ^[1]; Bell, R. E. ^[1]; Ethier, Stephane ^[1]; Ryan, Philip Michael ^[2]

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1. Princeton Plasma Physics Laboratory (PPPL)
2. ORNL

Various theories and numerical simulations support the conjecture that the ubiquitous problem of anomalous electron transport in tokamaks may arise from a short-scale turbulence driven by the electron temperature gradient. To check whether this turbulence is present in plasmas of the National Spherical Torus Experiment, measurements of turbulent fluctuations were performed with coherent scattering of electromagnetic waves. Results from plasmas heated by high harmonic fast waves show the existence of density fluctuations in the range of wave numbers k(perpendicular to)rho(e) = 0.1-0.4, corresponding to a turbulence scale length of the order of the collisionless skin depth. Experimental observations and agreement with numerical results from the linear gyro-kinetic GS2 code indicate that the observed turbulence is driven by the electron temperature gradient. These turbulent fluctuations were not observed at the location of an internal transport barrier driven by a negative magnetic shear.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1018276
• Journal Information: Nuclear Fusion, Vol. 49, Issue 5; ISSN 0029--5515
• Country of Publication: United States
• Language: English