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

Tao Lan; Sen Zhang; Weixing Ding; Ge Zhuang; Zhengwei Wu; Wenzhe Mao; Chen Chen; Shijie Lan; Hangqi Xu; Tijian Deng; Junfeng Zhu; Jiaren Wu; Yiming Zu; Defeng Kong; Shoubiao Zhang; Yuan Yao; Peng Yuan; Zian Wei; Haiyang Zhou; Hai Wang; Xiaohui Wen; Jie Wu; Chu Zhou; Ahdi Liu; Jinlin Xie; Hong Li; Chijin Xiao; Wandong Liu

doi:10.1063/5.0055570

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

Rev Sci Instrum. 2021 Sep 1;92(9):093506. doi: 10.1063/5.0055570.

Authors

Tao Lan¹, Sen Zhang¹, Weixing Ding¹, Ge Zhuang¹, Zhengwei Wu¹, Wenzhe Mao¹, Chen Chen¹, Shijie Lan¹, Hangqi Xu¹, Tijian Deng¹, Junfeng Zhu¹, Jiaren Wu¹, Yiming Zu¹, Defeng Kong², Shoubiao Zhang², Yuan Yao², Peng Yuan¹, Zian Wei¹, Haiyang Zhou¹, Hai Wang¹, Xiaohui Wen¹, Jie Wu¹, Chu Zhou¹, Ahdi Liu¹, Jinlin Xie¹, Hong Li¹, Chijin Xiao¹, Wandong Liu¹

Affiliations

¹ Department of Plasma Physics and Fusion Engineering, University of Science and Technology of China, Hefei 230026, China.
² Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China.

PMID: 34598546
DOI: 10.1063/5.0055570

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.