CONTROL OF TURBULENT WAVES BY END PLATE BIASING

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1)During the period of this research project, two diagnostic systems have been developed for the measurements of density fluctuations as well as density profiles of the GAMMA 10 tandem mirror.i)The 70 GHz Fraunhofer-diffraction apparatus has been newly installed to the centrall cell plasma (z=2.4m). A new rectangular antenna array which functions as a spectroscopic slit in the plane of observation enabled to attain a good signal to noiseratio.ii)The 7-18 GHz and 18-26 GHz, X-mode and O-mode reflectometers were also designed and have applied to the centrall cell plasma (z=0m and 1.8m) for the meausrements of radial distribution of the fluctuations.2)The potential control of plasmas was carried out by applying a bias voltage to the end plates for two operational modes of GAMMA 10. The main results are the following.i)In the ECRH-start mode with broad density profiles, the density fluctuations satisfying the dispersion relation of drift waves were suppressed by increasing the radial elect … More ric field regardless of its sign. The suppression of turbulence allowed the enhancement of the plasma parameters such as the density and the diamagnetic loop signal, and lowered the Halpha signal.ii)In the ICRF-start mode with narrow density profiles, the rotational instabilities with the lowest azimuthal mode number were predominantly excited during the formation of confining potentials. They were supressed by applying the moderate negative bias to lower the radial electric field.iii)The present study shows that it is possible to control plasma instabilities by shaping the radial potential profiles using segmented end plates so as to suppress radial ambipolar transport.3)The reflectometers have been appllied for the measurement of fluctuations with ion cyclotron range of frequency (ICRF).i)The wave with omega<omega_<ci> was identified as the electromagnetic Alfven ion cyclotron (AIC) wave.ii)It was shown that the internal magnetic fluctuations can be determined from the ratio of X-to O-mode signals.iii)The reflectometers was also used to monitor the applied ICRF, the deposition profile of the ICRF power. Less