Shrinking Kilometer-Scale Particle Accelerators to the Lab Bench

Work conducted at the Central Laser Facility (part of the Rutherford Appleton Laboratory, UK) by a group of international researchers, including EuPRAXIA collaborators, has led to the development of a new diagnostic technique to measure ultrashort electron beams produced by laser wakefield acceleration (LWFA). This may help bring powerful x-ray free-electron lasers (XFELs), currently several kilometers long, down to tabletop scales.

Schematic of the experimental setup.*

Conventional XFELs require extremely high-energy electron beams to generate the bright, ultrafast x-ray pulses used to image viruses and chemical reactions in real time. LWFA offers a much smaller alternative: by firing an intense laser pulse into a plasma, researchers create a wake of electric fields that can accelerate electrons to high energies, over just centimeters. One of the major challenges with this technique is that the resulting electron bunches are extremely brief, shorter than the time it takes light to traverse the width of a human hair, which has resulted in scientists having difficulty in measuring their properties with sufficient precision.

The team’s new technique overcomes this challenge by using the same laser that drives the wake to probe the electrons that it accelerates. The electrons interaction with the laser leads to tiny, controlled deflections. By precisely measuring these deflections, and knowing the oscillations of the laser field, the researchers can comprehend the electrons’ position and momenta, producing the first complete map of the beam’s structure and energy distribution.

This capability gives scientists a powerful diagnostic tool for refining LWFA performance, offering a path towards more stable, and higher-quality beams. In turn, this progress could accelerate the development of compact XFELs, pushing the EuPRAXIA project forward in its aim to address the need for more cost-efficient, reduced size, innovative and sustainable particle accelerator facilities. These developments will ultimately expand access to ultrafast x-ray imaging for biology, chemistry, materials science, and even future medical technologies.

Professor Rajeev Pattathil, deputy leader on EuPRAXIA Preparatory Phase Work Package 16, (WP 16 looks at the Technical Design Report for EuPRAXIA’s second laser driven plasma site), commented: “Laser-driven plasma accelerators are maturing to a level where advanced light sources such as XFEL facilities are being designed based on this technology. One of the prerequisites for this is the understanding of the temporal characteristics and energy of the accelerated electron bunches; simultaneous measurement of these is important.

By using the CLF’s Gemini laser system, the collaboration has come up with a diagnostic technique that enables this measurement. This is a major step towards future light sources based on laser-driven accelerator facilities such as CLF’s EPAC and EuPRAXIA”.

The full paper in PRX can be accessed here.

*Feature image: Schematic of the experimental setup. A horizontally lineally polarized laser pulse was focused on the entrance of a two-stage gas cell. A thin Kapton tape was placed after the gas cell to block the residual laser pulse. The LWFA-generated electron beam was deflected by a permanent magnet in the vertical direction to resolve the energy spectrum. (Image credit: Y.Ma, et al, Phys. Rev. X 15, 031062 https://doi.org/10.1103/sxqf-l6mp CC BY 4.0)

This article is based on an original article published on the STFC/CLF website here