• A N S Iyengar

      Articles written in Pramana – Journal of Physics

    • Stability-transport modeling of the SINP tokamak discharges

      S L Ahiri S Mukhopadhyay A N S Iyengar R Pal

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      A one-dimensional stability transport code has been developed to simulate the evolution of tokamak plasma discharges. Explicit finite-difference methods have been used to follow the temporal evolution of the electron temperature equation. The poloidal field diffusion equation has been solved at every time step. The effects of MHD instabilities have been incorporated by solving equations for MHD mixing and tearing modes as and when required. The code has been applied to follow the evolution of tokamak plasma discharges obtained in the Saha Institute of Nuclear Physics (SINP) tokamak. From these simulations, we have been able to identify the possible models of thermal conductivity, diffusion and impurity contents in these discharges. Effects of different MHD modes have been estimated. It has been found that in low q0 discharge m=1, n=1 and m=2, n=1 modes play major role in discharge evolution. These modes are found to result in the positive jump in the loop voltage which was also observed in the experiments. Hollow current density profile jφ and negative shear in the q profile have also been found in the rising phase of a discharge.

    • Investigations of low qa discharges in the SINP tokamak

      S Lahiri A N S Iyengar S Mukhopadhyay R Pal

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      Low edge safety factor discharges including very low qa (1<qa<2) and ultra low qa (0<qa<1) have been obtained in the SINP tokamak. It has been observed that accessibility of these discharges depends crucially on the fast rate of plasma current rise. Several interesting results in terms of different time scales like Tqa · τR etc have been obtained using a set of softwares developed at SINP. From fluctuation analysis of the external magnetic probe data it has been found that MHD instabilities m=1, n=1 and m=2, n=1 etc. play major role in the evolution of these discharges. To investigate the internal details of these discharges, an internal magnetic probe system has been developed using which current density jφ and other related parameters have been estimated. By carrying out a resistive stability analysis, evidence of the above-mentioned MHD instabilities have again been found. The physical processes lying behind the accessibility and evolution of the low qa discharges have been thoroughly investigated.

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