New insights into proton bunch self-modulation in plasmas

Published on

Plasma Cell installation
AWAKE Experiment - Plasma Cell installation. ©CERN

The AWAKE Collaboration, which includes members of the QUASAR Group, has just published an article that provides new insights into the self-modulation of a proton bunch in a plasma.

The paper, published in Physical Review Accelerators and Beams, presents numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path.

A detailed understanding of the proton self-modulation in a plasma is essential for optimising the process of plasma wakefield acceleration. The use of density gradients in the plasma offers the possibility to control the charge of the proton bunches and the frequency of the bunch modulation, which in turn determine the amplitude and phase velocity of the wakefield.

In particular, the researchers found in simulations that the charge of the modulated bunch with negative gradients is lower than with positive gradients, in agreement with previously published experimental data. The simulations also showed that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency revealed details about the evolution of the self-modulation process along the plasma.

The simulation and experimental results presented in the paper are in excellent agreement with each other. They complement and explain previously published results and show that many details of the self-modulation process predicted in the simulations are indeed observed in the experiment.

These findings will facilitate the optimisation of the plasma wakefield accelerator concept being developed in the AWAKE experiment.


More information:

Simulation and experimental study of proton bunch self-modulation in plasma with linear density gradients
P. I. Morales Guzmán et al. (AWAKE Collaboration)
Physical Review Accelerators and Beams 24, 101301 (2021)