Properties of fast solitary structures

We present detailed observations of electromagnetic waves and particle dist ributions from the Fast Auroral SnapshoT (FAST) satellite which reveal many important properties of large-amplitude, spatially-coherent plasma structu res known as "fast solitary structures" or "electron phase space holes". Si milar structures have been observed in several regions of the magnetosphere including the auroral zone, plasma sheet boundary layer, and bow shock. Th ere has been rapid theoretical progress in understanding these structures. Solitary structures can develop from bidirectional electron beams. Once dev eloped, the one-dimensional properties parallel to the magnetic field can b e adequately described by analytical treatment as BGK structures. There rem ains, however, several unanswered questions. The origin of the bidirectiona l electron beams, the development of two-or three-dimensional Structures, a nd the observed association with the ion cyclotron frequency are not well u nderstood.