Electron current disruption and parallel electric fields associated with electrostatic ion cyclotron waves

Laboratory observations of electron flux disruption by the potential well of a large‐amplitude ion cyclotron wave, which can be interpreted as electron trapping, are reported for the first time. Associated with trapping of more than 50% of the electron distribution is the existence of a weak electric field parallel to the external magnetic field. The significance of these observations, particularly to magnetospheric phenomena, is discussed.