Emittance Measurements of a Laser-Wakefield-Accelerated Electron Beam

Abstract : The transverse emittance of a relativistic electron beam generated by the interaction of a high-intensity laser with an underdense plasma has been measured with the “pepper-pot” method. For parameters pertaining to the forced laser wakefield regime, we have measured an emittance as low as (2.7±0.9) π   mm mrad for (55±2)   MeV electrons. These measurements are consistent with 3D particle-in-cell simulations of the experiment, which additionally show the existence of a relatively large halo around the beam core.