Study of x-ray radiation from a laser wakefield accelerator

Abstract

A Laser Wakefield Accelerator (LWFA) is under development at Lawrence Livermore National Laboratory (LLNL) to produce electron bunches with GeV class energy and energy spreads of a few‐percent. The interaction of a high power (200 TW), short pulse (50 fs) laser with neutral He gas can generate quasi‐monoenergetic electron beams at energies up to 1 GeV [1]. The laser pulse can be self‐guided over 1 cm overcoming the limitation of vacuum diffraction. X‐ray betatron radiation is emitted while the accelerated electrons undergo oscillations in the wakefield electrostatic field. Here we present electron spectra measurements with a two screen spectrometer allowing to measure both the electron energy and the transverse deflection at the plasma exit. We have measured monoenergetic electron beams above 300 MeV. Furthermore a forward directed x‐ray beam is observed. Preliminary measurements of the spectrum are in reasonable agreement with the calculated betatron spectrum in the synchrotron asymptotic limit using the measured electron beam parameters.