本文選題：等離子體診斷 + 偏振干涉儀��； 參考：《華中科技大學》2015年碩士論文

【摘要】：遠紅外激光診斷是托卡馬克實驗和運行的重要診斷手段,J-TEXT托卡馬克裝置具備兩套遠紅外激光診斷系統(tǒng):測量等離子體密度的HCN激光干涉儀系統(tǒng)和同時測量等離子體電子密度和電流剖面的三色遠紅外激光偏振干涉儀。HCN遠紅外激光干涉儀是實驗運行的必備診斷,提高信號質量必要性不言而喻。三色遠紅外偏振儀是J-TEXT裝置上深入開展物理實驗的重要診斷系統(tǒng),目前已實現(xiàn)0.1°相位分辨率,1μS的時間分辨率以及17道的空間測量,而激光光源的穩(wěn)定性直接關系到偏振儀的測量精度,因此,本論文的工作主要著力于兩個方面,第一,遠紅外干涉儀輸出中頻信號優(yōu)化;第二,用于穩(wěn)定偏振干涉儀光源的遠紅外激光器的反饋系統(tǒng)的建立。論文第一部分從HCN遠紅外激光干涉儀在實驗過程中出現(xiàn)的信噪比較差、易受放電干擾問題出發(fā),對干涉儀中頻信號的降噪優(yōu)化工作進行了具體介紹,主要內(nèi)容包括系統(tǒng)接地及屏蔽優(yōu)化、熱釋電探測器前級放大電路改造以及六階橢圓濾波電路的應用三個方面。在第二部分中,首先分析了由遠紅外激光器不穩(wěn)定引起的三波中頻信號頻率波動與信噪比下降問題對法拉第旋轉角測量精度的影響。之后根據(jù)三波法偏振干涉測量對激光器的特殊應用要求,闡述了傳統(tǒng)穩(wěn)頻方法在J-TEXT偏振干涉儀應用中的局限性,提出了以穩(wěn)定各激光器間頻率差為基本控制目標,并通過輸出功率反饋使激光器振蕩頻率跟蹤激活介質譜線中心頻率的激光器反饋方法。并對J-TEXT偏振干涉儀基于TMS320F2812數(shù)字信號處理器開發(fā)的激光器反饋系統(tǒng)的設計與搭建進行了詳細描述。為確保法拉第旋轉角的高精度測量,該反饋系統(tǒng)的建立不會對偏振干涉儀光路結構進行任何更改,并使用光電隔離技術避免了電磁耦合噪聲對偏振干涉儀測量可能產(chǎn)生的影響。經(jīng)過調(diào)試,反饋系統(tǒng)可將偏振干涉儀中頻信號的頻率波動限制在±12kHz以內(nèi),滿足50kHz帶寬數(shù)字濾波器的使用要求。同時激光器輸出功率可以長期維持在最大輸出功率的85%以上,保證了偏振干涉儀中頻信號信噪比大于50的設計要求。在文章結尾處,對反饋系統(tǒng)工作時偏振干涉測量法拉第旋轉角及弦積分密度的噪聲干擾及測量精度進行了驗證測試,結果令人滿意。
[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 擄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 鹵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.
【學位授予單位】：華中科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TL631.24;TN248

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