Laser Plasma Electron Linear Accelerator

The generation of an ultrashort relativistic electron bunch from a strong laser-plasma interaction have been studied by particle-in-cell simulations and observed experimentally. The electron beam was generated from the plasma created by focusing a Ti: sapphire 12 TW (tera watt) laser pulse at the edge of helium gas jet expanded into the vacuum from a pulsed supersonic nozzle. The laser pulse duration was 50 fs (femtosecond). In the interaction of 50 fs 12 TW laser pulse with plasma of density of 5×10 cm (γ = ωLaser/ωplasma=18.6) the electron beam generation was taking place due to the transverse injection of some portion of the plasma electrons which constitute a large amplitude plasma wave. Such an electron injection and generation took place at the very end of the interaction region with no possible chance for enhanced acceleration. For a relatively higher plasma density at 5×10 cm, (γ = 5.8) the electron generation with very high energy (up to 100 MeV) was observed in the simulation at the beginning of the interaction region. The relativistic force (in the laser’s propagation direction) of the laser pulse creates relativistic waves with wavelengths of the order of the laser wavelength propagating with the pulse. Due to its short length, the relativistic waves break into the wakefield behind the laser pulse producing energetic electrons. These electrons constitute the injection source for the following relativistic wave so these electrons acquire the maximal energy in the bunch just behind the laser pulse. In the experiment, the electron beam transverse profile and its total charge have been measured in the forward direction by using imaging plate and Faraday-cup, respectively. Corresponding author: Nasr A.M. Hafz, address is Nuclear Engineering Research Laboratory, Graduate School of Engineering, University of Tokyo, 22-2 Shirane Shirakata, Tokai-mura, Naka-gun, Ibaraki-ken, 319-1188 Japan. FAX: +81-29-287-8488. TEL: +81-29-287-8986. E-mail: [email protected]