CRAFT负离子源中性束注入系统400 keV加速器束流光学特性分析

Beamlet optics analysis of 400 keV accelerator for CRAFT negative ion based neutral beam injection system

负离子源中性束注入(NNBI)系统是聚变堆主机关键系统综合研究设施(CRAFT)的组成部分,其目标是开展NNBI相关的科学与工程问题研究,为未来聚变堆NNBI系统的研制与运行积累经验。加速器的束流光学特性决定着最终形成束流的发散性,进而影响着束流在加速器和束线中的传输效率,这对NNBI系统的高功率、高能量、长脉冲运行至关重要。为此,采用IBSimu离子束流模拟程序对目前CRAFT NNBI的400 keV加速器电极系统的物理设计进行束流光学特性分析与评估。目前该套电极结构的设计与ITER负离子源类似,束发散的计算结果满足设计要求。在负离子束流密度较高时(100~300 A/m^(2)范围内),具有更小束发散角;引出距离(5~7 mm范围内)和加速距离(88~110 mm范围内)的适当增加,也呈现出束发散角下降趋势。

The negative ion based neutral beam injection(NNBI)system is one of the testing or demonstrating systems in the frameworks of Comprehensive Research Facility of Fusion Technology(CRAFT).The object of the CRAFT NNBI system is to research the key physics and engineering issues around the NNBI,and to accumulate experience for future development and operation of the NNBI system for fusion reactor.The beamlet optics character of a negative ion accelerator determines the divergence of the formed beam,and further influences the beam transmission efficiency through the accelerator and the beamline,which is very important to the high-power,highenergy,and long-pulse operation of the NNBI system.Therefore,the ion beam simulation code IBSimu was used to analyze and estimate the physics design of the beamlet optics of the 400 keV accelerator for the CRAFT NNBI system.The IBSimu code has been successfully benchmarked and applied to many negative ion sources.The current design of the electrode aperture has a similar structure of the ITER negative ion source,the calculation results of the beamlet divergence can meet the design requirement.A higher extracted ion current density(between 100 to 300 A/m^(2))draws a lower beamlet divergence.When properly increasing the extraction gap(between 5 to 7 mm)or acceleration gap(between 88 to 110 mm),there is a decreasing tendency of the beamlet divergence.