Principles and applications of x-ray sources based on laser-plasma acceleration

One of the most prominent applications of modern particle accelerators is the generation of radiation. For example, in a synchrotron or an x-ray free electron laser (X-FEL), high energy electrons oscillating in periodic magnetic structures emit bright x-rays.

In spite of their scientific appeal that will remain evident for many decades, one limitation of synchrotrons and X-FELs is their typical mile-long size and their cost, which often limits access to the broader scientific community.

This tutorial will review the prospects of using plasmas produced by intense lasers as particle accelerators and x-ray light sources, as well as some of the applications they enable. A plasma is an ionized medium that can sustain electrical fields many orders of magnitude higher than that in conventional radiofrequency accelerator structures. When short, intense laser pulses are focused into a gas, it produces electron plasma waves in which electrons can be trapped and accelerated to GeV energies. This process, laser-wakefield acceleration (LWFA), is analogous to a surfer being propelled by an ocean wave. Many radiation sources, from THz to gamma-rays, can be produced by these relativistic electrons. Betatron x-ray radiation, for example, is produced when relativistic electrons oscillate during the LWFA process. This tutorial will also review several LWFA-driven sources in the keV-MeV photon energy range, including X-FELs, Compton Scattering, and bremsstrahlung sources.

An important use of x-rays from laser plasma accelerators we will finally discuss is their emerging applications, in particular in High Energy Density (HED) science. In these experiments, x-ray photons can pass through dense material, and absorption of the x-rays can be directly measured, via spectroscopy or imaging, to inform scientists about the temperature and density of the targets being studied.