Density modulation experiments within the full metallic wall and lithium limiter on the HT-7 tokamak

The methods to study the particle diffusion coefficient and the convection velocity were primarily based on the density modulation and the use of D2 gas puffing in the HT-7 tokamak. The density was measured by a five-channel far-infrared interferometer. The density modulation amplitude was 10% of the central chord average background density, and the modulation frequency was 7 Hz in experiments. For the reason that the wall condition and the types of the limiter will influence the transport coefficients, during this new experimental cycle we have improved the device on HT-7 such as updating the full metallic wall and making use of the lithium limiter, forming the new experimental condition we take advantage by determining the particle diffusion coefficient (D) and the convection velocity (V) and testing the coefficient changes under different wall conditions and the limiter. Apparently, D and V were obtained at different background plasmas (the central chord average density (ne)=1.5×1019 and 2.2×1019 m-3). It is observed that the influence of density modulation on the main plasma parameters is very weak, and a comparison will be discussed between the experimental data D, V under the lithium limiter and the ones under the carbon limiter.