Investigation of Charge Dependency in impurity transport in Aditya-U tokamak

Impurity transport in tokamak mostly anomalous, driven by fluctuations in plasma parameters. However, depending upon machine parameters and plasma conditions, transport can follow neo-classical theory. In neo-classical transport, diffusion coefficient in classical and Pfirsch-Schlüter regimes has no Z dependence, while in Banana-Plateau regime shows weak dependence on Z. Also, turbulent diffusion coefficient remains primarily independent of Z. In Aditya-U tokamak, along with intrinsic low Z impurities (C, O), many low and medium Z impurities (He, Ne, Ar) are introduced via gas puffing and wall coating (Li) into the plasma for different diagnostic and operation purposes. Then, transport studies for different Z present in Aditya-U are interesting due to the fact that Z dependencies of diffusion coefficients vary with machines. For this purpose, the experimental brightness profile of spectral lines 464.7 nm (C²⁺), 650 nm (O⁴⁺) and 377.7 nm  (Ne¹⁺) are measured with 1m long multi-track spectrometer. An indigenously developed impurity transport code by using semi-implicit numerical method is modeled experimental profiles to determine the transport coefficients of these impurity ions and a comparison is done to understand the charge dependency of impurity transport in tokamak plasma.