Hollow plasma channels are promising candidates for the acceleration of electron and positron beams, as the transverse forces are nearly vanishing inside the hollow channel, as long as the accelerated bunches are perfectly cylindrically symmetric and injected on the axis of the hollow channel structure. Furthermore, the accelerating fields can also be nearly constant provided that the accelerated bunch current profile is appropriately tailored. These features make it fundamentally possible to preserve beam quality during the acceleration . In realistic situations, however, small asymmetries in the beam profile or small misalignments between the beam and the hollow channel axis will seed the growth of the beam breakup instability, thus stopping the acceleration prematurely and degrading beam quality substantially. These beam breakup instabilities are a severe limitation on the use of hollow channels for particle acceleration .
Several schemes were recently proposed to stabilize hollow channel acceleration. For example, Pukhov et al. investigated electron acceleration in hollow channels with a plasma filament on axis and simulation results showed a stable acceleration in meter-long hollow channels . Amorim et al. studied hollow channels self-generated by a tightly focused positron beam and found regions of accelerating and focusing fields for positrons .
Here, we investigate a new mechanism for stabilization of positron acceleration in hollow channels. Using theory and particle-in-cell simulations with the code OSIRIS , we show that the ion motion associated with the wakefield ponderomotive force can form a hollow plasma channel self-consistently. The hollow plasma channel can then be excited by a second particle beam that drives a nonlinear plasma wave with positron focusing and accelerating fields. We investigate the possibility of high-quality acceleration in this scheme.
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|Working group||Laser-driven electron acceleration|