Dynamics of electron-beam holes induced by self-trapping

A phase-space distribution of a weak electron-beam injected into a cold plasma is experimentally investigated in electron time scales. It is shown that electron-beam holes in phase-space evolve dynamically from appearance to collapse, as synchronized with a wave packet dominated by a beam mode. The dependence of the hole velocity radii on the packet crest amplitudes indicates that the holes are induced by self-trapping of the beam. It is found that the beam is well trapped while the packet grows linearly, but easy to be detrapped after that.