Wave excitation, nonlinear scattering, and turbulence from an ion ring instability

An ion beam perpendicular to the magnetic field forms a ring distribution in velocity space, which is unstable. The ion ring instability excites lower hybrid waves linearly as well as whistler and magnetosonic waves nonlinearly via induced scattering. The driving ring velocity distribution may form naturally in the ionosphere and magnetosphere or be created artificially in an experiment. An upcoming experiment, SMART (Space Measurement of A Rocket-released Turbulence), will demonstrate these processes in the near-Earth space environment. In support of the SMART mission, we present detailed kinetic simulations of ion ring instabilities and the subsequent wave excitation, nonlinear scattering, and turbulence. As the ring instability develops, electrostatic lower hybrid waves and electromagnetic waves form as anticipated. The conversion of electrostatic to electromagnetic energy is efficient enough to deliver whistlers far away from the source region. As the initial ring temperature increases, the topology of the dispersion surface changes character. These simulation results are rigorously compared to the predictions of wave turbulence theory and were used to design the SMART experiment.