FLASHForward is a project to conduct Future-ORiented Wakefield Accelerator Research and Development at the DESY free-electron laser (FEL) facility FLASH. It focusses on the advancement of plasma-based particle acceleration technology with the overarching goal to realise usable plasma-driven FELs. Furthermore, the foreseen studies are a litmus test for plasma-wakefield accelerator technology to evaluate their potential for future use in highly demanding high-energy physics experiments.

Normalized particle density distribution of plasma electrons and a FLASHForward-type beam obtained from a 3D Particle-In-Cell simulation with the code OSIRIS. The beam excites a highly nonlinear plasma wave in the blowout regime with extreme electric fields

 

Plasma-based Wakefield Acceleration

In plasma-wakefield accelerators (PWFAs), relativistic charged particle beams traverse a plasma target and excite co-propagating plasma waves with extremely intense electromagnetic fields. The amplitude of these „wakefields“ exceeds the ones in today's state-of-the-art radio-frequency accelerators by several orders of magnitude. Electron beams (witness beams), injected into such wakefields gain energy at an enormous rate. This enables acceleration of electron-beams to high energies within very short distances, hence leveraging a dramatic miniaturisation and reduction of cost of prospective particle accelerators utilising plasma-based methods. Beams, today accelerated in kilometre-scale facilities, such as the European XFEL, may in future be accelerated in meter-scale plasma-based accelerators.

The capability of PWFAs to sustain extreme accelerating fields has been demonstrated in an experiment at the Stanford Linear Accelerator Center (SLAC) in 2006. Scientists focussed a 42 GeV electron beam into a plasma cell and observed an energy gain of electrons in the tail of the beam by more than 40 GeV within a distance of less than a meter. The experiment "Future-oriented wakefield-accelerator research and development at FLASH" (FLASHForward) at DESY will use electron-beams from the highly versatile accelerator FLASH to achieve further milestones on the road to harnessing PWFAs for applications in modern science. The most essential goals of FLASHForward are to:

• produce high-quality beams with electron-beam-driven acceleration,
• systematically analyse bunch parameters (normalised projected emittance, normalised uncorrelated emittance, bunch length) for different injection techniques,
• achieve transformer ratios greater than 2 (ratio of the witness and the driver energies),
• demonstrate for the first time an Free-Electron Laser (FEL), driven by plasma-accelerated electron beams.

Plasma-accelerator-driven FELs can have unique features, e.g. ultrashort bunch lengths, high beam brilliance or synchronization to a laser beam accurate at the femtosecond level, which will allow processes to be probed on time or length-scales which are not accessible by state-of-the-art conventional light sources. In addition, this novel light source will power high-brilliance X-ray beams in small-scale labs and open up a plethora of new research possibilities for chemistry, biology, materials science, etc.

Author: Dr. Timon Mehrling