OBSERVATION OF ION-CYCLOTRON TURBULENCE AT SMALL VALUES OF MAGNETIC-FIELD-ALIGNED CURRENT

Fluctuations in plasma density are observed in the ion-cyclotron frequ ency range in a Q-machine plasma column at values of magnetic-field-al igned current significantly below the critical value for current-drive n electrostatic ion-cyclotron (CDEIC) waves. These fluctuations arise from the inhomogeneous energy-density driven (IEDD) instability, are r elatively broadband, and can have large amplitude compared to CDEIC fl uctuations. These results impact the interpretation of ion heating and acceleration in the ionosphere, especially at low-altitude where magn etic-field-aligned current densities estimated to be large enough to b e supercritical to current-driven or beam-driven electrostatic ion-cyc lotron waves are rarely detected.