A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator

Abstract

Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7TW. The beam charge scales approximately with the laser energy and is limited by beam loading. For 40TW laser pulses we measure a maximum charge of almost 1nC per shot, originating mostly from electrons of less than 10MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1Hz repetition rate. In accordance with Geant4 Monte-Carlo simulations, we measure a γ-ray source size of less than 100μm for a 0.5mm tantalum converter placed at 2mm from the accelerator exit. Furthermore we present radiographs of image quality indicators.