The physical picture of beam loading in the blowout regime

The feasibility of laser/plasma wakefield accelerators depends upon the ability to efficiently load a bunch of electrons to the wakefield driven by a laser or an electron beam propagating through a plasma. Such accelerators are expected to operate in a nonlinear regime -the blowout regime-, where the driver is intense enough to push all plasma electrons aside. Since the properties of the accelerator are determined by the three dimensional shape of the wakefield in the blowout regime, a description of beam loading must involve the interaction between this shape and the accelerating electrons. In order for the quality of the accelerating beam to be high, the modification of the plasma structure due to the presence of the beam must be small. Maximizing the beam charge while maintaining its quality high requires tailoring of the beam profile. This tailored profile may then be scaled up for more powerful drivers.