Direct Observation of Plasma Waves and Dynamics Induced by Laser-Accelerated Electron Beams

Abstract

Plasma wakefield acceleration (PWFA) is a novel acceleration technique with promising prospects for both particle colliders and light sources. However, PWFA research has so far been limited to a few large-scale accelerator facilities world-wide. Here, we present first results on plasma wakefield generation using electron beams accelerated with a 100-TW-class Ti:Sa laser. Due to their ultrashort duration and high charge density, the laser-accelerated electron bunches are suitable to drive plasma waves at electron densities in the order of 10 19 cm −3 . We capture the beam-induced plasma dynamics with femtosecond resolution using few-cycle optical probing and, in addition to the plasma wave itself, we observe a distinctive transverse ion motion in its trail. This previously unobserved phenomenon can be explained by the ponderomotive force of the plasma wave acting on the ions, resulting in a modulation of the plasma density over many picoseconds. Due to the scaling laws of plasma wakefield generation, results obtained at high plasma density using highcurrent laser-accelerated electron beams can be readily scaled to low-density systems. Laser-driven PWFA experiments can thus act as miniature models for their larger, conventional counterparts. Furthermore, our results pave the way towards a novel generation of laser-driven PWFA, which can potentially provide ultra-low emittance beams within a compact setup.

Plasma accelerator-based ultrabright x-ray beams from ultrabright electron beams

“…At the same time, R&D will also be expanded to further linac-based PWFA-capable facilities, and to hybrid LWFA→PWFA approaches . 29,30 This will accelerate the development and prototyping of plasma photocathode electron guns as standardized ultrahigh brightness electron beam source technology, and will allow harnessing of the impact which is expected from ultrabright electron beams for applications such as light sources. Figure 7 provides a schematic overview on the plasma photocathode PWFA method as brightness transformer stage for electron beams from LWFA as well as from conventional linacs, in order to unlock realization of transformative light source applications such as X-FEL, ICS, and ICL on university-and industry-laboratory scale.…”

“…These are all-optical systems, where a laser-plasmaaccelerator system replaces the linac. 6,29,30 LWFA intrinsically produces electron beams with high current and charge densities, which are primary requirements for driving a PWFA stage. In fact, LWFA and PWFA are highly complementary 6,31,32 such that a clear directionality of combining them in hybrid LWFA→PWFA setups is highly attractive.…”

Application programmes at the Scottish Centre for the Application of Plasma-based Accelerators (SCAPA)

“…47 Such electron beams may have transformative impact on applications, such as realising 5 th generation light sources. 48,49 The extreme beams that are realisable by plasma accelerators and, in particular, by novel injection schemes such as down-ramp injection 35 and the plasma photocathode 46 also require novel diagnostics and measurement techniques. In this application theme, the plasma response to the interaction of electron beams and laser pulses with plasma will be exploited as a highly sensitive 'magnifying glass' to retrieve multi-dimensional fingerprints of the interaction.…”

Directions in plasma wakefield acceleration

“…A unique advantage of LWFA is the capability to produce ultrashort, intense electron packets with kiloampere-scale currents in especially compact set-ups. These electron packets can also be useful as beam drivers of PWFA stages in hybrid set-ups [23], an approach which is only just beginning to be systematically explored experimentally [24]. This avenue could multiply the availability of PWFA-ready systems and provide a further transformative step change for PWFA R&D. The main challenges here are the stability of LWFA electron-beam output, and controlled capture of these beams and insertion into PWFA stages as driver beams.…”