Convective velocity reversal caused by turbulence transition in tokamak plasma.
Particle transport has been studied in the Tore Supra tokamak by using modulated ion cyclotron resonance heating to generate perturbations of density and temperature. For the first time, a reversal of the particle convective velocity and a strong increase in the turbulent particle flux have been clearly observed. When the mixed critical gradient ζc=R/L(T)+4(R/L(n))=22 is exceeded, the particle flux increases sharply and the convective velocity reverses from inward to outward. These observations are in agreement with quasilinear, gyrokinetic calculations. The critical gradient corresponds to a transition from an instability driven by the ion temperature gradient to the onset of another instability caused by trapped electrons.
Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China.
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Zhong
CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
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Zou
CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
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Bourdelle
Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China.
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Song
CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
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Artaud
CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
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Aniel
Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China.
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Duan