The neutral beam injectors of the ITER experiment will rely on negative ion sources to produce 16.7 MW beams of H/D particles accelerated at 1 MeV. The prototype of these sources was built and is currently operated in the SPIDER (Source for the Production of Ions of Deuterium Extracted from a Radio frequency plasma) experiment, part of the Neutral Beam Test Facility of Consorzio RFX, Padua. In the SPIDER, the H⁻/D⁻ ion source is coupled to a three grid, 100 kV acceleration system. One of the main goals of the experimentation in SPIDER is to uniformly maximize the extracted current density; to achieve this, it is important to study the density of negative ions available in the proximity of the ion acceleration system. In SPIDER, line-integrated measurements of negative ion density are performed by a cavity ring down spectroscopy diagnostic. Its principle of operation is based on the absorption of the photons of a laser beam pulse by H⁻/D⁻ photo-detachment; the absorption detection is enhanced by trapping the laser pulse in an optical cavity, containing the absorbing medium (i.e., negative ions). This paper presents and discusses the CRDS diagnostic setup in the SPIDER, including the first measurements of negative ion density, correlated with the main source parameters.

中文翻译：

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负离子源 SPIDER 中腔衰荡光谱诊断的开发和首次运行

ITER 实验的中性束注入器将依靠负离子源产生 16.7 MW 的 H/D 粒子束，加速为 1 MeV。这些源的原型是在 SPIDER（从射频等离子体中提取的氘离子的生产源）实验中建造并运行的，该实验是帕多瓦 Consorzio RFX 的中性束测试设施的一部分。在 SPIDER 中，H ^- /D ^-离子源耦合到三栅 100 kV 加速系统。在SPIDER中进行实验的主要目的之一是使提取的电流密度均匀最大化。为此，研究离子加速系统附近可用的负离子密度非常重要。在 SPIDER 中，负离子密度的线积分测量由腔衰荡光谱诊断执行。其操作原理是基于将激光束脉冲的光子的由H的吸收^- / d ^-光脱离 通过在包含吸收介质（即负离子）的光腔中捕获激光脉冲，增强了吸收检测。本文介绍并讨论了 SPIDER 中的 CRDS 诊断设置，包括与主要源参数相关的负离子密度的首次测量。