Recently, the first direct measurement of a full 6D accelerator beam distribution was reported [B. Cathey, S. Cousineau, A. Aleksandrov, and A. Zhukov, Phys. Rev. Lett. 121, 064804 (2018)]. That work observed a correlation between energy and transverse coordinates, for which the energy distribution becomes hollowed near the transverse core. This hollowing is obscured when the 6D phase space is projected onto one- and two-dimensional axes. This article illustrates how a similar structure emerges from simulation of an initially uncorrelated, high density bunched beam as the result of velocity perturbation from initial nonlinear space charge forces. This phenomenon has not been widely recognized in accelerator systems, but parallels can be drawn to observations of laser-ionized nanoclusters and electron sources for diffraction. While this effect provides insight into the origin of the measured core correlation, it does not provide a complete description. A better reproduction of the measured structure can be obtained via self-consistent simulation through the radio-frequency quadrupole.

中文翻译：

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快速电荷重新分布，导致高强度离子束中的核空心化

最近，首次报道了完整的6D加速器光束分布的直接测量[B. Cathey，S。Cousineau，A。Aleksandrov和A.Zhukov，物理学。牧师 121，064804（2018）]。这项工作观察到能量和横向坐标之间的相关性，为此，能量分布在横向核心附近变得空洞了。当将6D相空间投影到一维和二维轴上时，将消除这种凹陷。本文说明了如何通过模拟初始不相关的高密度束状光束（由于初始非线性空间电荷力引起的速度扰动）而出现类似的结构。这种现象尚未在加速器系统中得到广泛认可，但是可以观察到激光电离的纳米团簇和用于衍射的电子源的相似之处。尽管此效果可深入了解所测核心相关性的来源，但并未提供完整的描述。