Speaker
Description
The Advanced Wakefield Experiment (AWAKE) recently demonstrated that a 400 GeV/c proton bunch can drive high amplitude plasma wakefields. To effectively excite wakefields, the drive bunch length should be on the order of the plasma electron wavelength (typically < 3mm). However, available proton bunches at CERN have an rms length of 6-12 cm. To be still able to excite high-amplitude wakefields, the experiment uses the plasma to modulate the bunch density, a process called the Seeded Self-Modulation. Transverse seed wakefields driven by the bunch in plasma act back on the bunch itself and periodically focus and defocus it, creating a microbunch train. This microbunch train can then resonantly excite a high amplitude plasma wakefield.
Using the two-screen diagnostic in AWAKE, we measured the transverse proton bunch distribution downstream the plasma exit and proved that: 1) a 400 GeV/c proton bunch self-modulates in plasma; 2) the driven wakefield amplitudes grows from their initial seed level along the bunch and along the plasma. In this contribution, we discuss the physics behind the seeded self-modulation process and show the experimental results.
