High energy electrons from interaction with a 10 mm gas-jet at FLAME

G. M. Grittani, M. P. Anania, G. Gatti, D. Giulietti, M. Kando, M. Krus, L. Labate, T. Levato, Y. Oishi, F. Rossi, L. A. Gizzi

Proceedings of SPIE, vol. 8779: Laser Acceleration of Electrons, Protons, and Ions II; and Medical Applications of Laser-Generated Beams of Particles II; and Harnessing Relativistic Plasma Waves III, Article Number: UNSP 87791B, (2013).

Abstract

In this paper we discuss the spectra of the electrons produced in the laser-plasma acceleration experiment at FLAME. Here a <30 fs laser pulse is focused via an f/10 parabola in a focal spot of 10 mu m diameter into a 1.2 mm by 10 mm rectangular Helium gas-jets at a backing pressure ranging from 5 to 15 bar. The intensity achieved exceeds 10(19) Wcm(-2). In our experiment the laser is set to propagate in the gas-jet along the longitudinal axis to use the 10 mm gas-jet length and to evaluate the role of density gradients. The propagation of the laser pulse in the gas is monitored by means of a Thomson scattering optical imaging. Accelerated electrons are set to propagate for 47,5 cm before being detected by a scintillating screen to evaluate bunch divergence and pointing. Alternatively, electrons are set to propagate in the field of a magnetic dipole before reaching the scintillating screen in order to evaluate their energy spectrum. Our experimental data show highly collimated bunches (<1 mrad) with a relatively stable pointing direction (<10 mrad). Typical bunch electron energy ranges between 50 and 200 MeV with occasional exceptional events of higher energy up to 1GeV.