| Plasma Accelerators

Laser-Driven Plasmas & Applications


Plasma Accelerators


A laser-plasma accelerator in action. The initially infrared laser pulse enters a plume of gas from the left. In the plasma, non-linear wavelength changes result in a wide range of new colours, seen here as the red, orange and blue flashes. The remaining laser energy aling with generated electrons exit to the right.

A laser-plasma accelerator followed by an active plasma lens, pillars of disruptive plasma-based accelerator technology. Credit: DESY, Simon Bohlen



Sub-Group Leader

Laser-driven plasma accelerators are leading a revolution

Much like a gas, plasma is a mixture of many particles constantly whizzing about. Unlike a gas, which consists of neutral atoms or molecules, a plasma is a mixture of ions and electrons. The charged nature of plasma particles gives rise to many interesting phenomena, from protecting our planet from violent sunstorms to complex instabilities. One of the most interesting properties of plasmas is the ability to support enormous electric fields. These fields, similar in nature to those used in conventional radio-frequency particle accelerators, can be harnessed to construct plasma-based accelerators, potentially reducing the size of electron accelerators by a factor of a thousand or more. The basic physics of how to set up such a high accelerating field was demonstrated by Tajima and Dawson in 1979, highlighting how a high intensity laser pulse traversing through a plasma can set up a plasma density oscillation in its wake. Electrons can then gain energy from this wave, much like a surfer behind a boat.

MPA4 science enables novel LPA applications

The research performed in the MPA4 group focusses on fundamentals of laser plasma accelerators along with developing real-life industrial and medical applications. Among the topics covered on the fundamental research side are studies into generating polarised electron beams, the guiding of laser pulses in the plasma, crucial for extracting electron beams with high energies, and developing advanced injection methods to control the properties of the generated electron beams, while the application research ranges from miniaturizing devices that up to now rely on standard RF accelerators, such as medical imaging or treatment sources, to developing entirely new concepts to replace or augment the capabilities of present-day large-scale RF sources.

Stable and robust electron beams over 8 hours

Continuously measured electron spectra over 8 hours with stable electron source. Credit: DESY, Simon Bohlen

Within this context, a few different projects are currently being pursued. The PLASMED X project is a proof-of-principle demonstration of a bright all-optical Thomson scattering source for X-ray fluorescence imaging. Currently much of XFI research is performed at synchrotrons, limiting the potential applicability of this imaging modality with important benefits, such as lowered dose, high resolution, lack of false positives and pharmacokinetic measurements. The PLASMED X all-optical source can become an important alternative to the currently employed large-scale light sources. The unique properties of Thomson scattering, such as high photon energies, well-directed X-ray emission and ultrashort pulse duration are all important for XFI. Specific challenges being worked on include the optimisation of the electron source and the scattering laser pulse to result in the highest possible number of electrons in a narrow bandwidth X-ray pulse as well as developing the platform into a robust and reliable machine, with long-term stability and repredocibility.

Another important aspect of accelerated electron beams is their spin polarisation. While often overlooked in simpler applications, spin alignment is a crucial for not only future headline machines as the large colliders, but also for material science and spin physics. Plasma accelerators as sources of polarised electron beams have recently received more attention, with numerous different methods to generate such spin-aligned beams proposed. The aim of the LEAP (Laser Electron Acceleration of Polarised beams) project is to demonstrate that laser-plasma accelerators are capable of generating spin-polarised electron beams. The project is a collaboration between MPA4, FTX-AST and also colleagues from Max Planck Institute for Nuclear Physics. The pre-polarisation of the plasma source, the electron dynamics as they are injected into the plasma accelerator and subsequently accelerated as well as the diagnosis of such polarised beams are research challenges undertaken in this project.