Experimental observation of the transition between hose and self-modulation instability regimes

Plasma-based acceleration is one of the most promising technologies for the development of compact accelerators providing high-quality beams for research, medical, and industrial applications. The interaction with the plasma, however, can produce detrimental effects on the particle beam, such as the hose-instability, and ultimately limit its implementation. Several methods have been proposed to suppress such a process, for instance, by triggering and bringing to saturation the self-modulation instability. In the framework of plasma acceleration, we present, for the first time, the experimental observation of the transition from hose to self-modulation instability regimes. The measurements are obtained by using an ultra-relativistic electron beam interacting with the plasma confined in a capillary. The results provide a more comprehensive picture of the beam-plasma interaction and are validated with complete particle-in-cell simulations.