Betatron radiation from laser wakefield accelerators and its applications

Abstract

This thesis will detail experimental research in to laser wakefield acceleration (LWFA), with a particular focus on LWFA's as compact sources of brilliant, hard synchrotron radiation, so-called betatron radiation. The first results presented are from an experiment where a ~10 TW laser pulse was focussed in to a clustered methane target. The presence of clusters enhanced the stability and tunability of the electron beam while maintaining similar electron beam peak energies and charges to other injection mechanisms. It also produced beams with three times larger transverse momentum in the laser polarisation direction, differentiating this injection mechanism from self- and ionisation-injection as well as hinting at a possible future use as a reliable source of polarised betatron radiation.

The primary result of this thesis follows, which is that a self-injecting, self-guided LWFA driven by a 100-200 TW laser pulse, with a long f/40 focussing geometry, showed an increase in betatron brightness to 2.8x10^24 photons/s/mm^2/mrad^2/0.1%BW, the highest brightness betatron source yet reported, along with a source size of approximately 300 nm inferred from spectral measurements of the almost 2 GeV electron beams and ~20 keV critical energy betatron x-ray beams. At longer acceleration lengths an additional, large injection of charge in to the wakefield dramatically increased the photon yield at moderate energies by a factor of 5-6.

The final result is the first demonstration that betatron radiation is suitable for imaging rapidly evolving phenomena. By studying shock propagation in solid density targets it will be shown that it can be used to qualitatively and quantitatively study the properties of the shock. It is shown that with the reported increase in photon number, betatron radiation can produce images of rapidly evolving phenomena of comparable quality to those taken in recent experiments at third and fourth generation light sources.