Experimental Studies Of Electrostatic Fluctuations And Turbulent Transport In The Boundary Of J-TEXT Tokamak

Decades of studies on tokamaks have shown that the cross-field transport is much higher than expected in the fusion research. This will decrease the performance of plasma confinement, and thereby has adverse influence on the applicability of the fusion reactors in the future. Most experimental results have shown that the anomalous transport is more obvious in the boundary region of tokamaks. Significant contributors to the anomalous transport are the electrostatic fluctuations. However, the origin of the anomalous transport is still an open question. Therefore, we do our best to study the electrostatic fluctuations and turbulent transport in the boundary of J-TEXT tokamak, and thereby provide the possibility for deepening the understanding of the nature of the anomalous transport. This will be of great importance in finding effective measures to suppress the turbulence and enhance the plasma confinement efficiency.Two sets of Langmuir probe systems have been built and operated as the primary diagnostic tools. The electrostatic fluctuations and their influence on the radial transport are studied for the first time in the boundary of J-TEXT tokamak. The intermittent burst events (IBEs) and their influence on the radial transport are analyzed. A set of poloidal electrostatic probe array has been designed to study the poloidal asymmetry of the electrostatic fluctuations in the Scrape-Off Layer (SOL). The influence of the discharge conditions on the poloidal distribution of the plasma parameters is analyzed. The chief work and experimental results are described below:(1) Two sets of Langmuir probe systems have been built. Different probe tips have been designed according to different experimental purposes, such as four-probe array, one-dimensional radial probe array, one-dimensional poloidal probe array, two-dimensional probe array, and so on.(2) Lots of programs for the probe signal processing have been developed. A lot of detailed information about electrostatic fluctuations can be achieved using them, such as turbulent spectrum, correlation functions, bispectrum, time-frequency spectrum, higher order moments statistics, and so on. (3) The electrostatic fluctuations and their influence on the radial transport in the boundary of J-TEXT have been presented for the first time. The E x B flow shear is observed near the Last Closed Flux Surface (LCFS), where the level of the fluctuations decreases significantly, the degree of correlation between fluctuations diminishes, and the radial gradients of the electron temperature and density are higher than the other radial positions. The experimental results verify that the BDT theory is suitable near the LCFS of J-TEXT.(4) The IBEs and their influence on the radial transport are analyzed by applying lots of different probe arrays. The results reveal that the IBEs have higher density and radial velocity than their surrounding plasma. The radial transport carried by the IBEs is about 25%～45%to the total transport. In ther-θplane, the direction of movement of the single IBE is random. The average velocity of the IBEs has similar properties, the radial velocity Vr≈400-600m/s, the poloidal velocity Vθ≈600～1800 m/s, the directions of motion are outwards along the radius and along the ion diamagnetic direction, respectively. The IBEs with higher amplitude have higher velocity in most situations.(5) The electrostatic fluctuations have intermittent properties, power-law decay with the type of S(f)(?)f-1 in the power spectra, and time-long-range correlation characters. These properties are consistent with the predictions of the self-organized criticality systems (SOC).(6) The electrostatic fluctuations have poloidal asymmetry characters. The studies on the density fluctuations reveal that the SOC properties are more significant in the outside of the midplane. The discharge conditions may influence the poloidal distribution of the plasma parameters.