Design of real-time data acquisition system for interferometer-based electron density diagnostics on EAST

Abstract

Laser-aided interferometers are employed as the common diagnostics for electron density measurements. On the EAST (Experimental Advanced Superconducting Tokamak), we have four main electron density diagnostics—the far-infrared hydrogen cyanide interferometer, polarimeter/interferometer, carbon dioxide (CO2) dispersion interferometer, and solid-state source interferometer. For interferometers, the phase difference brought by the change in electron density can be acquired via mixers. A real-time data acquisition (DAQ) system is needed to calculate the highly precise density values. In this paper, a field-programmable gate array is employed to implement the system with fast Fourier transform-based demodulation technology. A highly precise analog/digital converter is employed for readout and digitization of the waveform including multiple frequency signals from high-performance Schottky mixers. The system has been simulated, and the results show that it can meet the requirements of the accuracy of interferometers on the EAST. Furthermore, the framework of the DAQ system also offers a reference of the data processing method to the future laser-aided interferometers.