To realize stable negative ion beams for 100 s required in the neutral beam injector of JT-60SA, a physical model to control cesium (Cs) distribution inside the negative ion source has been developed in order to maintain the stable negative ion production at the plasma grid (PG) surface with Cs. In this work, to quantitatively evaluate Cs coverage on the PG, a three-dimensional Cs transportation code was introduced to consider the spatial Cs distribution in the source. The spatial temperature distribution of the chamber wall was also introduced in this model. As a result, the reasonable variation of the Cs coverage for 100 s was obtained, compared to that in the initial model. Based on the modified model, the operational temperature of the chamber wall was proposed to be less than 60 °C to suppress the desorption of Cs in the chamber wall and to sustain the stable negative ion production. In addition, it was also suggested that a slightly higher wall temperature before the operation leads to a decrease in the amount of Cs stored at the chamber wall, resulting in suppression of Cs consumption in the ion source.

中文翻译：

---

用于稳定长脉冲操作的 JT-60SA 负离子源中铯分布的分析

为了在 JT-60SA 的中性束注入器中实现 100 秒的稳定负离子束，开发了一种控制负离子源内铯 (Cs) 分布的物理模型，以保持等离子体中稳定的负离子产生带有 Cs 的网格 (PG) 表面。在这项工作中，为了定量评估 PG 上的 Cs 覆盖率，引入了三维 Cs 传输代码来考虑源中的空间 Cs 分布。该模型还引入了室壁的空间温度分布。结果，与初始模型相比，获得了 100 秒内 Cs 覆盖率的合理变化。基于修改后的模型，建议腔壁的操作温度低于 60°C，以抑制腔壁中 Cs 的解吸并维持稳定的负离子产生。此外，也有人提出，操作前壁温稍高会导致腔壁储存的Cs量减少，从而抑制离子源中Cs的消耗。