An approach for control of equilibrium field profile through the real-time plasma current in ADITYA-U and SST-1 tokamaks

Abstract

Pairs of external magnetic field coils placed outside the vessel maintain plasma equilibrium in tokamaks. The shape and position of the plasma column are determined and controlled by the temporal current profile in the external field coils. The temporal profile of the coil current mainly controls the horizontal movement of the plasma column, which keeps the plasma column at the vessel center. Hence, it is important to set and control the equilibrium profile according to the plasma current evolution and its profile. For this purpose, a controlled power supply is used to set the current in the coils as per the given reference profile. Currently, during plasma operation in the ADITYA-U and SST-1 tokamaks, a pre-programmed profile is used to generate the coil current profile, which is a passive form of control. For modern tokamak operations, however, real-time plasma control is essential. A novel technique has been devised for controlling the equilibrium field profile in ADITYA-U and SST-1 tokamaks using the real-time plasma current. To match the output current profile with the plasma current profile, a preconditioning system called Plasma Current Conditioning (PCC) is developed. To accomplish this, a MATLAB Simulink model of a 35-year-old power supply and a mathematical model of inverse control were developed, which generates the required reference profile in real time based on the current plasma profile. Using prior experimental data, the model has been exhaustively tested and validated.