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FIGURE 5: (a) Radial electric field (plasma gun not active); E× B shearing rate and decorrelation rate at (b) 220 μs, and (c) 340 μs; d) radial electric field (plasma gun active; shear maintained at 450 μs); E× B shearing rate and decorrelation rate at (e) 280 μs, and (f) 450 μs.
Density fluctuation levels, in particular in the FRC core, are substantially reduced via electrostatic biasing of the peripheral diverted (SOL) plasma, and the C-2 FRC lifetime is substantially extended. Core turbulence observations are qualitatively consistent with quenching of long wavelength ion modes via finite Larmor radius effects, For the first time, direct evidence for sustained turbulence reduction via E× B flow shear has been observed in FRC geometry. Similar to the well-documented observations in tokamak edge and core transport barriers [33,34], turbulence reduction requires that the radial shearing rate must exceed the ambient turbulence decorrelation rate. The observed radial transport barrier spans the transition region between closed and open flux surfaces, with the peak ExB shearing rate in the open fieldline region (SOL). The prospect of turbulence control across the FRC separatrix via E× B shear opens up the possibility of reducing radial thermal and particle loss from the confined FRC region, and hence advancing towards long-pulse FRC operation with reduced fueling and auxiliary heating requirements.
ACKNOWLEDGEMENTS
We gratefully acknowledge contributions, valuable discussions, and support of the experiments by T. Akhmetov of Budker Institute, D. Barnes, R. R. Clary, S.A. Dettrick, J. Douglass, E. Garate H.Y. Guo, D. Gupta,, S. Gupta, A. Ivanov, S. Korepanov, Y. Mok, S. Primavera, A. Necas, A. Smirnov, A. Sibley, M. C. Thompson, E. Trask, A. D. Van Drie, and the entire TAE team.
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