Long-time measurements of line-integrated plasma electron density using a two-color homodyne optical fiber interferometer

Abstract

A two-color homodyne Mach–Zehnder (M–Z) optical fiber interferometer with wavelengths of 1.55 and 1.31 µm was developed for long-time measurement of line-integrated plasma electron density. A novel phase difference demodulation algorithm based on a single 3 × 3 optical coupler was implemented in a two-color optical fiber interferometer scheme for the first time. Our laboratory tests showed that this new optical fiber interferometer could determine the phase shift due to the low-frequency ambient vibration and could maintain high phase resolution measurement. The resolution of the new interferometer was less than 0.04 rad in 1000 s, corresponding to a line-averaged electron density of less than 1.0 × 1019 m−2. Actual plasma discharge experiments performed on KTX-CTI, which is a new compact torus injector (CTI) constructed at the Keda Torus eXperiment (KTX), showed that this interferometer has excellent several-second stability.

Experimental setup for interaction between highly charged ions and laser-produced plasma near Bohr velocity energy region

“…除了上述被动测量方式外, 实验中还配备了由 中国科学技术大学兰涛教授提供的主动测量激光 光纤干涉诊断装置 [34] , 如图3所示. 利用一台掺铒单 频光纤激光器提供所需的诊断激光光源, 其激光波 长为1550 nm, 线宽为1 kHz, 输出功率为52.5 mW, 并由单模光纤进行传输, 以实现Mach-Zehnder光 学干涉.…”

“…利用一台掺铒单 频光纤激光器提供所需的诊断激光光源, 其激光波 长为1550 nm, 线宽为1 kHz, 输出功率为52.5 mW, 并由单模光纤进行传输, 以实现Mach-Zehnder光 学干涉. 可测量的等离子体截止密度上限为 n c = 4.6 × 10 20 cm -3 [34] .…”