SUPPRESSION OF PLASMA FLUCTUATIONS IN THE TRANSITION TO THE IMPROVED-CONFINEMENT REGIME WHEN THE CURRENT IS RAISED RAPIDLY IN THE FT-2 TOKAMAK

Collective scattering of CO2-laser radiation is used to study the micr oturbulence of the plasma in the FT-2 tokamak when the current is rapi dly raised, while the magnetic-field shear is varied appreciably. The experiment exhibited suppression of the plasma fluctuations, the appea rance time of which was correlated with the transition of the discharg e to the improved-confinement regime. The resulting data are evidence that the suppression of the oscillations occurred predominantly in the central zone of the tokamak, and a suppression-extending phenomenon o r hysteresis is detected. The evolution of the spectral characteristic s of the fluctuations during the suppression is analyzed, using model calculations of the magnetic-held shear. (C) 1997 American Institute o f Physics.