Abstract
We demonstrate experimentally that a relativistic electron bunch shaped with a sharp rising edge drives plasma wakefields with one to seven periods along the bunch as the plasma density is increased. The plasma density is varied in the range. The wakefields generation is observed after the plasma as a periodic modulation of the correlated energy spectrum of the incoming bunch. We choose a low bunch charge of 50 pC for optimum visibility of the modulation at all plasma densities. The longitudinal wakefields creating the modulation are in the MV/m range and are indirect evidence of the generation of transverse wakefields that can seed the self-modulation instability, although the instability does not grow significantly over the short plasma length (2 cm). We show that the seeding provides a phase reference for the wakefields, a necessary condition for the deterministic external injection of a witness bunch in an accelerator. This electron work supports the concept of similar experiments in the future, e.g., SMI experiments using long bunches of relativistic protons.
- Received 9 August 2013
DOI:https://doi.org/10.1103/PhysRevLett.112.045001
© 2014 American Physical Society