J-TEXT偏振干涉仪远红外激光器反馈系统的建立

发布时间：2018-05-17 12:01

本文选题：等离子体诊断 + 偏振干涉仪　；参考：《华中科技大学》2015年硕士论文

【摘要】：远红外激光诊断是托卡马克实验和运行的重要诊断手段,J-TEXT托卡马克装置具备两套远红外激光诊断系统:测量等离子体密度的HCN激光干涉仪系统和同时测量等离子体电子密度和电流剖面的三色远红外激光偏振干涉仪。HCN远红外激光干涉仪是实验运行的必备诊断,提高信号质量必要性不言而喻。三色远红外偏振仪是J-TEXT装置上深入开展物理实验的重要诊断系统,目前已实现0.1°相位分辨率,1μS的时间分辨率以及17道的空间测量,而激光光源的稳定性直接关系到偏振仪的测量精度,因此,本论文的工作主要着力于两个方面,第一,远红外干涉仪输出中频信号优化;第二,用于稳定偏振干涉仪光源的远红外激光器的反馈系统的建立。论文第一部分从HCN远红外激光干涉仪在实验过程中出现的信噪比较差、易受放电干扰问题出发,对干涉仪中频信号的降噪优化工作进行了具体介绍,主要内容包括系统接地及屏蔽优化、热释电探测器前级放大电路改造以及六阶椭圆滤波电路的应用三个方面。在第二部分中,首先分析了由远红外激光器不稳定引起的三波中频信号频率波动与信噪比下降问题对法拉第旋转角测量精度的影响。之后根据三波法偏振干涉测量对激光器的特殊应用要求,阐述了传统稳频方法在J-TEXT偏振干涉仪应用中的局限性,提出了以稳定各激光器间频率差为基本控制目标,并通过输出功率反馈使激光器振荡频率跟踪激活介质谱线中心频率的激光器反馈方法。并对J-TEXT偏振干涉仪基于TMS320F2812数字信号处理器开发的激光器反馈系统的设计与搭建进行了详细描述。为确保法拉第旋转角的高精度测量,该反馈系统的建立不会对偏振干涉仪光路结构进行任何更改,并使用光电隔离技术避免了电磁耦合噪声对偏振干涉仪测量可能产生的影响。经过调试,反馈系统可将偏振干涉仪中频信号的频率波动限制在±12kHz以内,满足50kHz带宽数字滤波器的使用要求。同时激光器输出功率可以长期维持在最大输出功率的85%以上,保证了偏振干涉仪中频信号信噪比大于50的设计要求。在文章结尾处,对反馈系统工作时偏振干涉测量法拉第旋转角及弦积分密度的噪声干扰及测量精度进行了验证测试,结果令人满意。
[Abstract]:Far-infrared laser diagnosis is an important diagnostic method in Tokamak experiment and operation. J-TEXT tokamak has two far-infrared laser diagnostic systems: HCN laser interferometer system for measuring plasma density and simultaneous plasma measurement system. Three-color far-infrared laser polarization interferometer with bulk electron density and current profile. HCN far-infrared laser interferometer is a necessary diagnosis for experimental operation. The necessity of improving signal quality is self-evident. The trichromatic far infrared polarimeter is an important diagnostic system for further physical experiments on J-TEXT. At present, the time resolution of 0.1 掳phase resolution of 1 渭 S and the spatial measurement of 17 channels have been realized. The stability of laser light source is directly related to the measurement accuracy of polarimeter. Therefore, the work of this paper mainly focuses on two aspects: first, the if signal output of far-infrared interferometer is optimized; second, The establishment of a feedback system of far infrared laser used to stabilize polarization interferometer light source. In the first part of this paper, the problem of low signal-to-noise ratio (SNR) and easy to be disturbed by discharge in HCN far-infrared laser interferometer is introduced in detail. The main contents include system grounding and shielding optimization, retrofit of front amplifier circuit of pyroelectric detector and application of sixth order elliptical filter circuit. In the second part, the effect of frequency fluctuation and SNR decrease of three-wave intermediate frequency signal caused by the instability of far-infrared laser on the measurement accuracy of Faraday rotation angle is analyzed. Then according to the special application requirements of the three-wave polarization interferometry, the limitation of the traditional frequency stabilization method in the application of J-TEXT polarization interferometer is expounded, and the basic control target is to stabilize the frequency difference between the lasers. The laser feedback method is used to track the center frequency of the active dielectric line by output power feedback. The design and construction of laser feedback system based on TMS320F2812 digital signal processor for J-TEXT polarization interferometer are described in detail. In order to ensure the high precision measurement of Faraday rotation angle, the establishment of the feedback system will not make any changes to the optical circuit structure of the polarization interferometer, and the possible effect of electromagnetic coupling noise on the polarization interferometer measurement can be avoided by using optoelectronic isolation technique. After debugging, the feedback system can limit the frequency fluctuation of if signal of polarization interferometer to 卤12kHz, which can meet the requirements of 50kHz bandwidth digital filter. At the same time, the output power of the laser can be maintained over 85% of the maximum output power for a long time, which ensures the design requirement of the if signal to noise ratio of the polarization interferometer greater than 50. At the end of the paper, the noise interference and measurement accuracy of Faraday rotation angle and chord integral density measured by polarization interference during the operation of the feedback system are verified and the results are satisfactory.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TL631.24;TN248

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