Electron bunch compressors formed of achromat arcs have a natural advantage over the more commonly used chicane compressors in that linearization of the longitudinal phase space is of the correct sign to compensate for the curvature imprinted by rf acceleration. Here we extend the utility of arc compressors to enable variation of the longitudinal compaction within a fixed footprint. We also show that this variability can be achieved independently order by order in momentum deviation. The technique we employ consists of additional dipoles, leading to the advantageous property that variability can be achieved without incurring significant penalty in terms of chromatic degradation. We show this by comparison to an alternative system where additional quadrupoles are utilized to enable variation of momentum compaction. Each of these alternative approaches are being considered in the context of an upgrade of the MAX IV linac, Sweden, to enable a soft x-ray free-electron laser in addition to its existing functions.

中文翻译：

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弧形可变束压缩机

由消色差弧形成的电子束压缩机与较常用的锥角压缩机相比具有自然的优势，因为纵向相空间的线性化具有正确的符号，可以补偿由rf加速度引起的曲率。在这里，我们扩展了电弧压缩机的用途，以使纵向压实能够在固定的占地面积内变化。我们还表明，可以在动量偏差中逐级独立地实现此可变性。我们采用的技术由额外的偶极子组成，从而带来了有利的特性，即可以实现可变性而不会在色差方面造成重大损失。通过与使用其他四极杆以使动量压实度变化的替代系统进行比较，我们显示了这一点。