Development of a dual HCN laser interferometer on a small tokamak device

Abstract

Abstract A dual hydrogen cyanide (HCN) laser interferometer system was designed and developed to measure the electron density of plasma with high temporal resolution. The system comprises two terahertz continuous wave (CW) discharge-pumped HCN lasers, each emitting at a frequency of 0.89 THz and with an output power of up to 100 mW. The intermediate frequency (IF) signal is obtained by adjusting the length of the resonant cavity. The temporal resolution of the interferometer can reach 1 μs when the intermediate frequency is at 1 MHz. The feasibility of the dual HCN laser interferometer system was verified by simulating the plasma using a wedge. Preliminary experimental results were obtained on a small tokamak device, a root mean square error of the dual HCN laser interferometer is approximately 1.5×1017 m-3 when the line-integrated electron density obtained by the dual HCN laser interferometer is about 1.5×1019 m-3.