ABSTRACT
A long, narrow, relativistic charged particle bunch propagating in plasma is subject to the self-modulation (SM) instability. We show that SM of a proton bunch can be seeded by the wakefields driven by a preceding electron bunch. SM timing reproducibility and control are at the level of a small fraction of the modulation period. With this seeding method, we independently control the amplitude of the seed wakefields with the charge of the electron bunch and the growth rate of SM with the charge of the proton bunch. Seeding leads to larger growth of the wakefields than in the instability case.
ABSTRACT
We present an electron injection scheme for plasma wakefield acceleration. The method is based on a recently proposed technique of fast electron generation via laser-solid interaction: a femtosecond laser pulse with the energy of tens of mJ hitting a dense plasma target at 45^{∘} angle expels a well collimated bunch of electrons and accelerates these close to the specular direction up to several MeVs. We study trapping of these fast electrons by a quasilinear wakefield excited by an external beam driver in a surrounding low density plasma. This configuration can be relevant to the AWAKE experiment at CERN. We vary different injection parameters: the phase and angle of injection, the laser pulse energy. An approximate trapping condition is derived for a linear axisymmetric wake. It is used to optimize the trapped charge and is verified by three-dimensional particle-in-cell simulations. It is shown that a quasilinear plasma wave with the accelerating field â¼ 2.5 GV/m can trap electron bunches with â¼ 100 pC charge, â¼60µm transverse normalized emittance and accelerate them to energies of several GeV with the spread â² 1% after 10 m..
