On "Efficiency versus Instability in plasma accelerators"

Recently in a paper by Lebedev et al it was demonstrated that the efficiency of the energy transfer from the drive bunch to the witness bunch in the plasma wakefield accelerator has a limit due to the BBU instability of the witness bunch. It was stated that the efficiency-instability relation is universal and thus should be considered as a fundamental limit. In this note, we show that recent results on the short-range wakefields indicate that this relation should be modified and conclusions of the paper by Lebedev et al should be reconsidered. In particular, we argue that the efficiency-instability relation produces only the lower bound for efficiency and thus does not produce a fundamental limit.