Real-time plasma electron density feedback control system based on FPGA on J-TEXT

Abstract

The J-TEXT newly deployed three-wave polarimeter-interferometer (POLARIS) system provides a better time and spatial resolution of the plasma electronic density than the old HCN interferometer system. The plasma electron density feedback control system is implemented on the already existing POLARIS DAQ system which is based on FlexRIO FPGA. Another FlexRIO board with an output module is added to implement the feedback control algorithm and feed the output to the piezoelectric crystal valve. The density feedback control system is able to extract the phase difference information from the intermedia frequency signal using FFT, calculate density of multiple channels and output control signal to the piezoelectric crystal valve in real-time. NI P2P technology is used to transfer processed data from a FlexRIO board to another in real-time without using the CPU. This system is also able to calculate density profile. With the density profile it can use compensated central chord line integrated or average density as control target. Also the real-time density profile data is useful for future plasma control system and disruption detection system.