Large-amplitude electrostatic ion-cyclotron wave phenomena and their relationship to magnetospheric events

Nonlinear interactions between current-driven, large-amplitude, electrostatic ion-cyclotron (EIC) waves and the velocity distributions of plasma electrons and ions were investigated. The interest was motivated by satellite observations of polar magnetospheric phenomena that occur in the presence of EIC waves. In the first set of experiments, a gridded electrostatic energy analyzer recorded the electron distributions at various times within one EIC wave period. A significant disruption of the electron flux, periodic with the EIC wave frequency, was found. This is interpreted as evidence for strong trapping of the electron distribution by the wave's potential well. Using a capacitive probe to measure axial and radial changes in the plasma potential, a magnetic-field-aligned static electric field was found in the presence of large-amplitude EIC waves. In the second set of experiments, EIC wave phenomena were studied in a two ion species (barium and potassium) plasma. Qualitative agreement with the linear theory was found for EIC-wave amplitudes just above the onset of the instability. In the large amplitude steady state, both EIC modes exist in only a small range of the relative ion-density ratio indicating the presence of some nonlinear interaction