强流离子源光腔衰荡光谱应用研究

强流离子源是托卡马克中性束注入器的核心部件，为了满足未来对高能量离子束中性化效率的要求，负离子源成为中性束注入系统的首选。光腔衰荡光谱(cavity ring-down spectroscopy，CRDS)是一种超高灵敏探测吸收光谱技术。在强流负离子源中，利用氢负离子的光致剥离过程，CRDS可以用来测量氢负离子的绝对积分密度。与激光光致剥离法与光学发射光谱法相比，CRDS具有不受电磁干扰、不依赖等离子体参数、测量精度高等优点。强流离子源负离子密度测量所用CRDS系统由激光器、光学谐振腔、光电探测器和数据采集系统四部分组成。本文根据CRDS测量氢负离子密度的原理，详细推导了氢负离子密度的计算方法，给出了氢负离子密度测算表达式；然后，结合强流离子源实验室应用的具体情况，分析了各部分装置的选择原则与注意事项；最后，介绍了CRDS技术在德国马克斯-普朗克等离子体物理研究所、日本国立聚变科学研究所、意大利Consorzio RFX研究所强流负离子源研究中的应用情况。实验结果表明，源腔气压、源功率等源参数会影响氢负离子密度；铯的注入可以将氢负离子密度从1016 m-3量级提高到1017 m-3量级；同时，日本NIFS的实验结果证明氢负离子密度与引出电流呈线性关系。

Study on Cavity Ring-Down Spectroscopy in High Power Ion Source

High power ion source is a core component of neutral beam injector for tokamak. Negative ion source is the reference source for ITER neutral beam injection system as negative ion beam has a high neutralization efficiency in high energy. Cavity ring-down spectroscopy (CRDS) is a highly sensitive optical absorption spectroscopic technique. CRDS is able to measure the absolute line-of-sight integrated density of negative hydrogen ions based on photodetachment process. Compared with laser photodetachment method and optical emission spectroscopy, CRDS is insensitive to electromagnetic interference and doesn’t need plasma parameters for calculating, thus yielding reliable results. CRDS system is composed of laser, optical cavity, detector and data acquisition system. Equipment selection principle was analyzed. The basic principle of CRDS was presented, and then the analytical form of using CRDS to measure H- density was derived in detail. CRDS has already been applied to high power ion source in laboratories of Germany, Japan and Italy. Results displayed that source parameters, including pressure and power, affected H- density. H- density increased from 1016 m-3 magnitude to 1017 m-3 magnitude in Cs seeded operation. The linearity between H- density and extracted current was proved by NIFS.