ULTRA-SHORT X-RAY RADIATION COMING FROM A LASER WAKEFIELD ACCELERATOR

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 ultimate goal is to provide a bright and compact photon source for high energy density physics. The interaction of a high power (200 TW), short pulse (50 fs) laser with neutral He gas can generate quasi-monoenergetic electrons beams at energies up to 1 GeV [1]. The laser pulse can be self-guided over a dephasing length of 1 cm (for a plasma density of 1.5 x 10{sup 18} cm{sup -3}) overcoming the limitation of vacuum diffraction. Betatron radiation is emitted while the accelerated electrons undergo oscillations in the wakefield electrostatic field. Here we present electron spectrum measurements with a two screen spectrometer allowing to fix the ambiguities due to unknown angle at the plasma exit. We have measured monoenergetic electron beams at energies around 110 MeV. Furthermore a forward directed x-ray beam is observed. The peak energy of the measured synchrotron spectrum is reconstructed based on the energy deposited after different sets of filters, assuming x-ray radiation described in the synchrotron asymptotic limit (SAL) and is found around 6 keV.