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Description
High efficiency is essential for plasma-wakefield accelerators to be a cost-effective alternative for high-power applications, such as a linear collider. However, in a plasma-wakefield accelerator the beam-breakup instability can be seeded by a transverse offset between the driver and trailing bunch. This instability, which rapidly increases the oscillation amplitude of the trailing bunch, grows with higher power-transfer efficiency from the driver to the trailing bunch [V. Lebedev et al., Phys. Rev. Accel. Beams 21, 059901 (2018)]. We discuss the efficiency–instability relation with simulations using the 3D quasi-static PIC code HiPACE++. Using a grid of simulations, we examine the strength of the instability at different efficiencies across the parameters that contribute to the instability (beam loading, normalized wake radius) for a given plasma density. We find that the previously proposed efficiency–instability relation represents a lower limit on the strength of the instability for a given efficiency.
