2017 - 06 - 29
In the field of plasma acceleration, investigating how electron beams can be injected in a plasma wave is of critical importance, because the method used for this purpose strongly determines the final quality of the accelerated beams.
Thus, the laser wakefield acceleration community has always been very active in devising and demonstrating various injection techniques to obtain progressively improved beam qualities.
In a recent paper , Francesco Massimo and colleagues from Laboratoire d'Optique Appliquée (LOA) have presented a theoretical and numerical study on an injection scheme called density transition injection or shock-front injection.
This easy-to-implement scheme has already demonstrated experimentally to produce high quality electron beams [2-4]. Electron injection is triggered by a sharp density transition (often called shock-front) created in a gas jet through a blade. As the laser passes the shock-front density peak, the wakefield electron cavity behind the laser pulse is enlarged, trapping some of the electrons from the density transition.
The investigation performed by LOA focuses on the beam quality dependence on the density transition characteristics and on the physical mechanisms involved in this injection technique. The beam qualities envisaged in this study make the shock-front injection an appealing option for the EuPRAXIA injector.
 Massimo F. et al. 2017 Plasma Phys. Control. Fusion 59 085004  Schmid K. et al. 2010 Phys. Rev. ST Accel. Beams 13 091301  Buck A. et al. 2013 Phys. Rev. Lett. 110 185006  Thaury C. et al. 2015 Sc. Rep. 5 16310
PIC simulation of the density transition injection process shown with snapshots of the electron density at time t = 0, t = 63 fs, and t = 1032 fs.