Structured Plasmas for Laser-Driven-Control of Electron Beams

• Applicant: Dr. Robert Shalloo
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 531352484

Laser plasma accelerators (LPAs) are an emerging technology combining powerful femtosecond lasers with plasmas to accelerate charged particles to relativistic energies. They are spearheading a new generation of ultra-compact sources of electron and photon beams owing to their ability to support accelerating fields on the scale of hundreds of GV/m — more than three orders of magnitude larger than their conventional radio-frequency accelerator counterparts. This dramatic reduction in machine size opens up the possibility of distributing GeV-class accelerators not just at large-scale national laboratories, but at universities, hospitals and factories, greatly increasing the availability of beams for applications in areas of high societal impact, such as photon science, particle physics, medicine and industry. One concrete, near-term goal of significant interest is the use of a multi-GeV electron beam from an LPA to create a compact water-window X-ray free-electron laser (X-FEL). Such a machine would represent an important advancement in the adoption of plasma technology and would open up a clear route to significantly increasing accessibility to fourth generation X-ray light sources while reducing the environmental and financial costs of such machines. The most pressing challenge on the roadmap to realising this bold objective is the reliable generation and control of multi-GeV electron beams of exceptional quality from an LPA. This is critical, as it is the fundamental building block for a compact X-FEL. In recent years, exceptional progress has been made separately in pushing LPAs to the multi-GeV regime and in generating beams of FEL-quality. However, achieving both figures of merit simultaneously has yet to be demonstrated. The main objective of this project is the reliable generation of multi-GeV electron beams of high-quality compatible with driving a compact water-window X-FEL. This will be achieved through the programmatic optical structuring of the 3D plasma density profile in an LPA to unprecedented levels. Additionally, precise control of the laser propagation through this plasma structure will be essential. The optical tailoring of the plasma will facilitate two critical tasks: 1) the guiding of a high-intensity laser pulse over the centimetre-scale distances required for producing high-energy electron beams and 2) the implementation of a new plasma-based technique for controlling the injection of a high-quality electron bunch at the beginning of the accelerator. Machine-learning-driven optimisation and control techniques will be used to tune the laser and plasma parameters in concert to achieve stable acceleration of a kiloampere class electron bunch up to multi-GeV energies with sub-micron normalised emittances in a plasma stage just a few cm long.

• DFG Programme: Independent Junior Research Groups