The Experimental Study Of Zonal Flows In Confinement Improvement Induced By Electrode Biasing And Core Collective Scattering System

The zonal flows, which have toroidal and poloidal symmetry, are important in magnetized plasmas, since they gain energy from turbulence without extra transport and the shear of ZFs can also suppress ambient turbulence. Electrode biasing (EB) is an efficient way to artificially change the E x B shear in the edge of plasma and improve the confinement. The two branches of ZFs, the Low Frequency Zonal Flow (LFZF) and Geodesic Acoustic Mode (GAM), and their interaction with turbulence during con-finement improvement induce by EB are investigated in this thesis. Besides, a new Intermediate Frequency (IF) method is studied to extract the velocity information from scattering data, and the author successfully verified the existence of core GAM with this new method.The experiments of the interaction between ZFs and AT using Langmuir probe arrays are applied on J-TEXT tokamak. Two long distance coherent modes are found during confinement improvement induce by EB. They are confirmed to be LFZF and GAM with potential fluctuation m=n=O. GAM is observed during biasing H-mode for the first time. Poloidal wavenumber kθ is found to takes an important position in the sup-pression of the radial particle flux. The shear rate of mean flow and ZFs are compared. It is found that the propagation rate of AT (γAT= 2.1×106s-1) is bigger than any of the shear of mean flow (ωE×B,Biasing= 1.5×106s-1) or ZFs (γE×B,GAM= 0.71×10s-1), the biasing H-mode was achieved with the shearing effects of both. This experiment comfirmed the key role of ZF in the comfinement improvement and also indicates the ZFs’trigger effect on the biasing H-mode.Another work in this thesis is about the IF method. As the poloidal velocity is usually much larger than the velocity of turbulence in Tokamak devices, the Doppler Shift always predominate the data of scattering diagnostics. The IF method is developed to extract the velocity information from the fluctuation of density in which the Doppler Shift is dominated. We use the data from the CO2 laser coherent scattering diagnostic on HT-7 tokamak. The IF method code successfully obtains the poloidal velocity from the density fluctuation. The coherence of two velocities at different poloidal positions parted 180 degree shows that the coherent mode is poloidally symmetric. And the mode frequency also consistent with the theoretical GAM frequency, which confirms this core GAM. The signal to noise ratio is also tested and the result show that this new IF method is useful and can expand the measured quantities of such diagnostics.