Reaching high energies with a plasma-wakefield accelerator may require use of multiple stages. This coupling of beams from one stage to another can be nontrivial due to a combination of high divergence and non-negligible energy spreads. In addition, a number of other requirements must be met, such as space-efficient in- and out-coupling of the driver, matching of beta functions, dispersion cancellation, and ensuring synchronization and alignment to within extremely tight tolerances. Satisfying all these requirements takes up space between the stages, which can significantly reduce the effective gradient of the accelerator. We review the challenges, the technical requirements, and some currently proposed methods for solving (or circumventing) the staging problem.

中文翻译：

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等离子体尾波加速器的升级

使用等离子韦克菲尔德加速器达到高能量可能需要使用多个阶段。由于高发散和不可忽略的能量散布的结合，光束从一个阶段到另一阶段的耦合可能是不平凡的。另外，还必须满足许多其他要求，例如节省空间的驱动器的内外耦合，β函数的匹配，色散消除以及确保同步和对齐以在极严格的公差范围内。满足所有这些要求会占用级之间的空间，这会大大降低加速器的有效坡度。我们回顾了挑战，技术要求以及一些当前提出的解决（或规避）分期问题的方法。