Extrem Plasma Acceleration: Intensive Research and Highly Innovativ France-Germany – APERITIF-A

Laser-driven plasma accelerators are capable of delivering beams of several hundred MeV with acceleration distances of only a few centimetres. However, despite these impressive results the shot to shot reproducibility of the particle beam produced by this technique remains low in comparison with that of conventional accelerators. For some of the possible applications of these laser-driven plasma accelerators, this can be a severe limitation. The limited reproducibility may come from the regime in which the electrons were produced in most experiments so far: in the so-called “bubble regime” the plasma excitation is very strong, leading to wavebreaking in which some electrons from the plasma are accelerated in a very high gradient. This regime has been very successful in producing and accelerating electrons to high energies (more than 100 MeV/mm) but it is intrinsically non-linear and the electrons that are accelerated also come from the plasma itself in a partially uncontrolled way. This may explain the difficulty to have reproducible results from one shot to the next in terms of electron energies but also energy spread and total beam charge or beam pointing.
In the following project, we propose to operate a laser-driven plasma accelerator in a different regime where the plasma excitation is not so strong. In this regime, the forces in the plasma remain linear or quasi linear and consequently the acceleration should be less sensitive to any kind of fluctuation. In addition, there is no wavebreaking in this regime and thus the electrons have to be injected from an external source such as a photoinjector and a RF accelerator. Using RF accelerators coupled with high-power lasers, both in France and in Germany, we will investigate this scheme with the hope of demonstrating highly stable electron beam accelerated with a high gradient.