Sub-fs Electron Bunch Generation with Sub-10-fs Bunch Arrival-Time Jitter via Bunch Slicing in a Magnetic Chicane

摘要

The generation of ultra-short electron bunches with ultra-small bunch arrival-time jitter is of vital importance for Laser-plasma wake field acceleration (LWFA) with external injection. We study the production of 100-MeV electron bunches with bunch durations of sub-femtosecond (fs) and bunch arrival-time jitters of less than 10 fs, in an S-band photoinjector by using a weak magnetic chicane with a slit collimator .The beam dynamics inside the chicane is simulated by using two codes with different self-force models. The first code separates the self-force into a three-dimensional (3D) quasi -static space-charge model and a one-dimensional CSR model, while the other one starts from the first-principle with a so-called 3D sub-bunch method. The simulations indicate that theCSR effect dominates the horizontal emittance growth and the 1D CSR model underestimatesthe final bunch duration and emittance because of the very large transverse -to-longitudinal aspect ratio of the sub-fs bunch.Particularly, the CSR effect is also strongly affected by the vertical bunch size. Due to the coupling between the horizontal and longitudinal phase spaces , the bunch duration at the entrance of the last dipole magnet of the chicane is still significantly longer than that at the exit of the chicane, which considerably mitigates the impact of space-charge and CSR effects on the beam quality. Exploiting this effect , a bunch charge of up to 4.8 pC in a sub-fs bunch could be simulated.In addition, we analytically and numerically investigate the impact of different jitter sources on the bunch arrival-time jitter downstream of the chicane , and define the tolerance budgets assuming realistic values of the stability of the linac for different bunch charges and compression schemes.