Negative ion sources for neutral beam injection (NBI) in fusion experiments are based on the surface production of H- or D- on cesiated low work function surfaces. In the recent years, it was demonstrated at the large RF driven ion source of the ELISE (Extraction from a Large Ion Source Experiment) test facility that the requirements for the ITER NBI systems can be fulfilled by hydrogen. This is a big step toward the first operational period of ITER, planned for up to 2035. However, for the following operational period, neutral beam systems working in deuterium are needed. Operation of negative hydrogen ion sources in deuterium is significantly more demanding than in hydrogen: the amount of coextracted electrons is much higher and their increase during pulses is much more pronounced, limiting the achievable performance. This paper presents the results of investigations aimed to improve the insight into the physics related to this isotope effect. Due to the higher atomic mass of deuterium, cesium is removed much more effectively from reservoirs at the walls, resulting in a depletion of these reservoirs and a strongly increased cesium density in the plasma. Additionally, a correlation between the fluxes of charged particles toward the inner ion source surfaces and the coextracted electrons is identified.

中文翻译：

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在 ELISE 形成大的负氘离子束

聚变实验中用于中性束注入 (NBI) 的负离子源基于在铯化低逸出功表面上产生的 H- 或 D-。近年来，在 ELISE（从大型离子源实验中提取）测试设施的大型射频驱动离子源证明，氢气可以满足 ITER NBI 系统的要求。这是向 ITER 第一个运行期迈出的一大步，计划到 2035 年。然而，在接下来的运行期，需要在氘中工作的中性束系统。在氘中操作负氢离子源比在氢中要求更高：共提取电子的数量要高得多，而且它们在脉冲期间的增加要明显得多，从而限制了可实现的性能。本文介绍了旨在提高对与这种同位素效应相关的物理学的洞察力的调查结果。由于氘的原子质量较高，铯从壁处的储层中被更有效地去除，导致这些储层的耗尽和等离子体中铯密度的强烈增加。此外，还确定了带电粒子流向内部离子源表面与共提取电子之间的相关性。