Particle-beam-driven plasma wakefield acceleration

In a way analogous to laser-plasma accelerators (also called Laser WakeField Accelerators, LWFA), waves of electron density in the plasma can also be driven by the passage of a relativistic beam of charged particles, the “driver”. For very dense electron beam drivers, the plasma wave takes the form of an ion cavity (see figure), in the so-called blow-out or bubble regime. This ion cavity has ideal properties to accelerate the main electron beam, the “trailing” electron bunch.

Principle of Electron driven plasma wake acceleration

The UPX group is exploring the physics of particle-beam-driven Plasma WakeField Acceleration (PWFA) by following several research avenues:

– Based on experiments conducted on the state-of-the-art conventional accelerator facilities FACET and FACET-II, the group aims at understanding the physics of beam-plasma interaction and at the experimental realization of a plasma accelerator module that would be capable of accelerating a distinct bunch of particles, with high energy gain, low energy spread, high energy efficiency, and preserved emittance. Among the many recent achievements, one can cite the 9 GeV acceleration of electron beam in a PWFA (PPCF 58, 034017, 2016), the demonstration of high-field acceleration and electron-beam self-focusing (Nature Communications 7, 11898, 2016), the multi-GeV acceleration of positrons in a self-loaded PWFA (Nature 524, 442, 2015) and first acceleration of a distinct bunch of positrons in a plasma (Sci. Rep. 7, 141180, 2017), and the first measurements of transverse wakefields in hollow plasma channels (PRL 120, 124802, 2018). This research is conducted as part of the international E-200 collaboration, including in particular SLAC and UCLA in the US.

– Using a Laser WakeField Accelerator (LWFA), one can actually produce electron beams whose properties reach the very demanding requirements to drive a PWFA. Such hybrid wakefield accelerators, where a LWFA electron beam drives a PWFA section, open the opportunity to study PWFA physics using in-house compact laser facilities and to leverage the advantages of PWFA, for example for the generation of ultra-bright particle beams. Recent achievements include the observation of plasma lensing and acceleration from the PWFA section, as well as the imaging of the PWFA plasma wave. This research on hybrid LWFA-PWFA is conducted in collaboration with HZDR and LMU in Germany.

In addition to these experimental activities, the group is also contributing in the theoretical and advanced numerical modeling of beam-plasma interaction. This activity includes the topic of hybrid LWFA-PWFA, the acceleration of positrons in plasmas as well as electromagnetic plasma instabilities developing during the interaction between laser, particle beam and plasma. Recently, a new concept that leverages hybrid LWFA-PWFA for the generation of ultra-bright betatron gamma-ray radiation was demonstrated numerically (PRL 120, 254802, 2018). This work is conducted in collaboration with CEA in France.