Phase-Space Holes in an Electron-Beam-Plasma
  It is shown in an electron-beam-plasma system that phase-space holes evolve dynamically in electron time scales from appearance to collapse. The holes are synchronized with a wave packet dominated by a beam mode, and their velocity radii depend on the packet crest amplitudes. This suggests that the holes are induced by a self-trapping phenomenon. It seems from the observed images that the trapped-beam is hard to be detrapped while the packet grows linearly, but easy to be done after that. 
Tsuyoshi Takeda, Yamagiwa Keiichiro