Profile Aided Real-Time Plasma Electron Density Feedback Control Based on FPGA on J-TEXT

The J-TEXT newly deployed three-wave polarimeter–interferometer (POLARIS) system provides a better temporal and spatial resolution of the plasma electronic density than the that of old HCN interferometer system. The new plasma electron density feedback control system is implemented on the already existing POLARIS data acquisition system which is based on FlexRIO field-programmable gate array (FPGA). An analog output card is added to control the piezoelectric crystal valve of the gas puffing. The density feedback control system is able to extract the phase-shift information from the intermediate frequency signal using fast Fourier transform, calculate density of multiple chords, and output control signal to the piezoelectric crystal valve in real time. NI P2P technology is used to transfer data from a FlexRIO FPGAs to another in real time without using the CPU; thus, all FlexRIO FPGAs onboard can calculate the density with only one acquiring the reference chord signal. This system is also able to calculate density profile. With the density profile, it can use compensated central chord integrated or average density as control target. Also, the real-time density profile data are useful for the future plasma control system and disruption detection system.