Spontaneous collimation of relativistic electron beams due to a high-contrast laser in conjunction with a cone-shaped target*

Achieving Inertial Fusion Energy (IFE) through Inertial Confinement Fusion (ICF) requires a high conversion efficiency of laser energy into the internal energy of the fuel. The fast ignition, which directly heats the fuel with a heating laser, is potentially highly efficient. However, the huge divergence angle of the relativistic electron beam (REB) generated by the heating laser makes ignition unrealistic.

Here, we demonstrate the spontaneous collimation of REB due to a high-contrast laser in conjunction with a cone-shaped target. When the high-contrast laser propagates inside the cone, it reflects on the cone walls, directing the laser toward the central axis of the cone.  Consequently, the electrons accelerated at the cone tip are directed toward the central axis of the cone, resulting in the spontaneous collimation of REB. 

We utilized a tracer target to observe the propagation of REB in this study. The experiment was conducted on a petawatt kilojoule-class laser, LFEX, at Osaka University. A plasma mirror was placed just before the target irradiation to achieve high contrast in the laser. This presentation will discuss the details of the experiment and the results obtained.