Laser-seeded modulation instability in a proton driver plasma wakefield accelerator

Abstract

A new method for initiating the modulation instability (MI) of a proton beam in a proton driver plasma wakefield accelerator using a short laser pulse preceding the beam is presented. A diffracting laser pulse is used to produce a plasma wave that provides a seeding modulation of the proton bunch with the period equal to that of the plasma wave. Using the envelope description of the proton beam, this method of seeding the MI is analytically compared with the earlier suggested seeding technique that involves an abrupt truncation of the proton bunch. The full kinetic simulation of a realistic proton bunch is used to validate the analytic results. It is further used to demonstrate that a plasma density ramp placed in the early stages of the laser-seeded MI leads to its stabilization, resulting in sustained accelerating electric fields (of order several hundred MV/m) over long propagation distances ($100-1000 m). V C 2013 AIP Publishing LLC.

Effect of beam emittance on self-modulation of long beams in plasma wakefield accelerators

“…[10][11][12][13][14] The SMI works properly only if a selected instability mode is somehow externally seeded. 2,[15][16][17] Otherwise, non-axisymmetric perturbations (hosing modes) belonging to the same instability family 18 could develop and destroy the beam. Even the axisymmetric modes are sufficient to destroy the beam, if several of them grow concurrently.…”

Path to AWAKE: Evolution of the concept

“…A short electron bunch [42], a powerful laser pulse [43], a sharp cut in the bunch current profile [40,44], or a relativistic ionization front copropagating within the drive bunch can seed the SMI quite well. Analytical and numerical calculations, however, have shown that bunches with long rise times (longer than or about the plasma wavelength) do not produce stable bunch trains [30,38,39].…”

Physics of beam self-modulation in plasma wakefield accelerators

“…[26]. Various options are possible for the seed perturbation: a short electron bunch [26], a powerful laser pulse [27], a sharp cut in the bunch current profile [18], or a relativistic ionization front co-propagating with the drive bunch [28]. Currently, the co-propagating relativistic front is considered as the mainstream variant, as this solution is chosen for AWAKE experiment.…”