A new type of miniature plasma particle accelerator

A novel plasma-based particle accelerator has been realised, using a miniaturised version of a concept which until now had been possible only in a small number of large facilities worldwide.

An international collaboration, involving the University of Strathclyde, combined two kinds of plasma accelerators to achieve a rapid energy gain of electrons in only a few millimetres.

The accelerator could offer a compact source of high-quality electron beams for applications such as x-ray generation, material science and biomedical research.

The research builds on a concept previously proposed by one of the Strathclyde researchers, Professor Bernhard Hidding. It has been published in the journal Nature Communications.

Particle accelerators are behind some of the most spectacular scientific discoveries and are the reason why it is known that matter consists of atoms, and that, in turn, atoms consist of electrons Mpositively charged ions.

These electrons and ions are not only key building blocks of matter but can themselves be used to realise powerful particle accelerators. By transient separation of negatively charged electrons and positively charged ions, plasma wave oscillations can be excited. In devices known as laser wakefield accelerators (LWFA), the plasma wave is driven by an intense laser pulse.

Electrons can be injected into these plasma waves and then ‘surf’ on the plasma waves until they become out of phase with the wave. This scenario limits the quality, and rapid energy gain, of injected electrons. Using an intense electron beam as driver of a plasma wave, an approach known as PWFA, in contrast, generates a plasma wave which injected electrons can surf without dephasing.

The concept suggested 10 years ago by Professor Hidding and others proposed using the intense electron beam produced by LWFA and then using this electron beam to drive a separately attached PWFA stage. This ‘hybrid laser-plasma wakefield accelerator’ concept has, in recent years been developed by a European collaboration with researchers from Strathclyde and partner institutions in Germany and France.

In two complementary experiments at HZDR Dresden and LMU Munich, the collaboration demonstrated the flexibility and potential of the approach. The experiments show that the electron beam generated in specially designed LWFA stages can be fed into an attached but decoupled PWFA stage, where it drives a strong plasma wave. A plasma-injected electron beam can be post-accelerated here, and thus receives an energy boost.

Thomas Heinemann, a PhD student at Strathclyde and one of the lead authors of the study, said: “Our compact, hybrid plasma wakefield accelerator can serve as platform to explore and develop key plasma wakefield physics, such as energy boost, wakefield dynamics, and novel injection methods. Instead of being exclusively limited to overseas experiments at large facilities with limited beamtime and access, we can now study these issues also at home, in complementary parameter regimes.”

Professor Hidding said: “One of the most intriguing aspects is the automatic synchronization of laser and electron beams. This can in next steps enable realization of compact plasma photocathodes for ultrabright electron beam production.” Such ultrabright electron beams have transformative potential - for example, to drive ultracompact yet high-performance hard x-ray free-electron-lasers.

The hybrid plasma accelerator platform and applications can in the future be realized in the UK at SCAPA, the Scottish Centre for the Application of Plasma-based Accelerators, in which Strathclyde is a partner, and EPAC, the Extreme Photonics Applications Centre.

Partners in the research were: Helmholtz-Zentrum Dresden–Rossendorf; Technische Universität Dresden; DESY (Deutsches Elektronen-Synchrotron DESY), Hamburg; the Cockcroft Institute, Warrington; Ludwig–Maximilians–Universität München; Max Planck Institut für Quantenoptik, Garching; LOA, ENSTA Paris; CNRS/Ecole Polytechnique; Institut Polytechnique de Paris and CASUS (Center for Advanced Systems Understanding) Görlitz. Germany

The UK part of the research was funded by the European Research Council, through the NeXource project, the Science and Technology Facilities Council, through the PWFA-FEL project, and by the Cockcroft Institute and the Engineering and Physical Sciences Research Council.