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Propagating a short, relativistically intense laser pulse in a plasma channel makes it possible to generate comb-like electron beams – sequences of synchronized, low phase-space volume bunches with controllable energy difference. The tail of the pulse, confined in the accelerator cavity (electron density “bubble”), transversely flaps, as the pulse head steadily self-guides. The resulting oscillations of the cavity size cause periodic injection of electrons from ambient plasma, creating an energy comb with the number of components, their energy, and energy separation dependent on the channel radius and pulse length. Accumulation of noise (continuously injected charge) can be prevented using a …

Laser wakefield acceleration of electrons in the blowout regime can be controlled by tailoring the laser pulse phase and the plasma target. The100nm-scale bandwidth and negative frequency chirp of the optical driver compensate for the nonlinear frequency red-shift imparted by wakefield excitation.This mitigates pulse self-steepening and suppresses continuous injection. The plasma channel suppresses diffraction of the pulse leading edge, further reducing self-steepening, making injection even quieter. Besides, the channel destabilizes the pulse tail confined within the accelerator cavity (the electron density “bubble”), causing oscillations in the bubble size. The resulting periodic injection generates background-free comb-like beams – sequences of synchronized, …