One of the requirements of Heating and current drive Neutral Beam injectors for ITER is a beam homogeneity greater than 90%, to achieve an optimal beam transmission while keeping the heat load consistently low on the acceleration electrodes. The large size and complexity of ITER negative ion source play a key role in determining the homogeneity of the negative ion current of each of the 1280 beamlets and their divergence, and it is studied in the full-scale prototype source SPIDER. In this work the plasma properties are studied by spectroscopic and electrostatic measurements in the drivers, where the plasma is generated, and in the expansion region, where the plasma drifts and negative ions are produced, and they are correlated with the properties of the beam. The non-homogeneous plasma density profile is related to the non-homogeneous availability of negative ions along the beam vertical profile, with and without cesium evaporation. Visible tomography, a technique capable of characterizing isolated beamlet properties, is used to study the beam’s dependence on plasma uniformity along the entire beam profile. Using these tools, it has been demonstrated how an increase in plasma density is linked to an improvement in beam homogeneity. The latter has been directly correlated with plasma homogeneity. The magnetic filter field and biases of the plasma grid and bias plate are responsible for the variation in plasma density and its homogeneity. Non-uniformities in the plasma’s top/bottom and left/right distributions have been studied and partially addressed experimentally. The first issue was resolved by adjusting the radio-frequency power supplied to the plasma in different vertical regions, while the second issue was addressed by reversing the direction of the magnetic filter field and increasing the plasma density.

中文翻译：

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全尺寸ITER负离子束源早期运行中源参数与束流特性的相关性

ITER 的加热和电流驱动中性束注入器的要求之一是束流均匀性大于 90%，以实现最佳束流传输，同时保持加速电极上的热负荷始终较低。 ITER 负离子源的大尺寸和复杂性对于确定 1280 个子束中每个负离子流的均匀性及其发散度起着关键作用，并在全尺寸原型源 SPIDER 中进行了研究。在这项工作中，通过在产生等离子体的驱动器以及产生等离子体漂移和负离子的扩展区域中的光谱和静电测量来研究等离子体特性，并且它们与光束的特性相关。非均匀等离子体密度分布与沿束垂直分布的负离子的非均匀可用性相关，有或没有铯蒸发。可见光断层扫描是一种能够表征孤立子束特性的技术，用于研究光束对沿整个光束轮廓的等离子体均匀性的依赖性。使用这些工具，已经证明了等离子体密度的增加如何与束流均匀性的改善相关。后者与血浆均匀性直接相关。磁过滤场以及等离子体网格和偏置板的偏置是造成等离子体密度及其均匀性变化的原因。等离子体的顶部/底部和左/右分布的不均匀性已经被研究并通过实验部分解决。第一个问题是通过调整不同垂直区域提供给等离子体的射频功率来解决的，而第二个问题是通过反转磁过滤场的方向并增加等离子体密度来解决的。