Beam-Self-Trapping Phenomena in an Electron-Beam-Plasma

It is observed that electron-beam holes in phase-space evolve dynamically from arising to collapsing in electron time scales in an electron-beam-plasma system. The holes are synchronized with a wave packet dominated by a beam mode of the two-stream instability, and their velocity radii depend on the amplitudes of the packet crests. This shows that the holes are induced by the self-trapping of the beam. The observed images indicate that the holes keep alive due to the hard detrapping of the beam during the packet linear growth, but begin to collapse due to the easy detrapping in the packet saturation.