Xiong C Y, Chen J, Li Q, Liu Y, Gao L
State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, China.
Rev Sci Instrum. 2014 Dec;85(12):123502. doi: 10.1063/1.4902564.
A three-wave laser polarimeter-interferometer, equipped with three independent far-infrared laser sources, has been developed on Joint-TEXT (J-TEXT) tokamak. The diagnostic system is capable of high-resolution temporal and phase measurement of the Faraday angle and line-integrated density. However, for long-term operation (>10 min), the free-running lasers can lead to large drifts of the intermediate frequencies (∼100-∼500 kHz/10 min) and decay of laser power (∼10%-∼20%/10 min), which act to degrade diagnostic performance. In addition, these effects lead to increased maintenance cost and limit measurement applicability to long pulse/steady state experiments. To solve this problem, a real-time feedback control method of the laser source is proposed. By accurately controlling the length of each laser cavity, both the intermediate frequencies and laser power can be simultaneously controlled: the intermediate frequencies are controlled according to the pre-set values, while the laser powers are maintained at an optimal level. Based on this approach, a real-time feedback control system has been developed and applied on J-TEXT polarimeter-interferometer. Long-term (theoretically no time limit) feedback of intermediate frequencies (maximum change less than ±12 kHz) and laser powers (maximum relative power change less than ±7%) has been successfully achieved.
在联合TEX托卡马克装置（J-TEXT）上，已研制出一种配备三个独立远红外激光源的三波激光偏振计干涉仪。该诊断系统能够对法拉第角和线积分密度进行高分辨率的时间和相位测量。然而，对于长时间运行（>10分钟），自由运行的激光器会导致中频出现较大漂移（约100 - 约500千赫/10分钟）以及激光功率衰减（约10% - 约20%/10分钟），这会降低诊断性能。此外，这些影响会导致维护成本增加，并限制其在长脉冲/稳态实验中的测量适用性。为解决这一问题，提出了一种激光源的实时反馈控制方法。通过精确控制每个激光腔的长度，可同时控制中频和激光功率：将中频控制在预设值，同时将激光功率维持在最佳水平。基于此方法，已开发出一种实时反馈控制系统并应用于J-TEXT偏振计干涉仪。已成功实现了对中频（最大变化小于±12千赫）和激光功率（最大相对功率变化小于±7%）的长期（理论上无时间限制）反馈。
