Eur. Phys. J. Special Topics 175, 77-82 (2009)
DOI: 10.1140/epjst/e2009-01121-8

Recent results at LULI on fast electron transport with and without guiding cone in the context of fast ignitor

S.D. Baton¹, M. Koenig¹, J. Fuchs¹, L. Gremillet², C. Rousseaux², D. Batani³, A. Morace³, M. Nakatsutsumi⁴, R. Kodama⁴, T. Norimatsu⁴, A. Nishida⁴, F. Dorchies⁵, C. Fourment⁵, J.J. Santos⁵, J. Rassuchine⁶ and T. Cowan<sup>6

1</sup>  LULI, École Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau Cedex, France
²  CEA DIF, BP. 12, 91680 Bruyères-le-Châtel, France
³  Università di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
⁴  Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, 565-0871 Osaka, Japan
⁵  CELIA, Université Bordeaux 1, CNRS, CEA, 33405 Talence Cedex, France
⁶  Department of Physics, University of Nevada, Reno, 89557 Nevada, USA

Abstract
We present experimental and numerical results obtained at LULI (Laboratoire pour l'Utilisation des Lasers intenses) on propagation and energy deposition of laser-generated fast electrons into conical targets. The experimental measurements were performed by means of several diagnostics in order to assess the predicted benefit of conical targets over standard planar ones. Various configurations have been tried, regarding the laser parameters with the aim of optimizing the laser-to-target coupling. Our best results have been obtained when the laser was frequency-doubled at 0.53 μm, corresponding to interaction conditions without laser pedestal due to the ASE (Amplified Spontaneous Emission). Our data pinpoint the detrimental influence of the pre-plasma generated by the laser pedestal at 1.057 μm, whose confinement is enhanced in conical geometry as evidenced by shadowgraphic measurements which is also confirmed by 2D Cu-Ka transverse images obtained from Cu cones. The consequence is the filling of the cone, preventing the laser beam from efficiently reaching the cone tip. These experimental results are compared to 2D PIC simulations modeling of the laser-cone interaction.

© EDP Sciences, Springer-Verlag 2009