Particle-in-cell simulation study of the impact of ion cyclotron waves on auroral kilometric radiation

摘要

We will present results of 2 1/2-dimensional particle-in-cell simulations where the impact of ion cyclotron waves on auroral kilometric radiation (AKR) has been studied. A horseshoe electron distribution function in a strong magnetic field is unstable to modes with frequencies slightly below the electron cyclotron frequency and can generate AKR. In the presence of an electron beam superimposed on the horseshoe distribution, the system is unstable to ion cyclotron waves with phase velocity parallel to the magnetic field equal to the electron beam velocity. Ion cyclotron waves are often observed near the source region of AKR and have been predicted to have an influence on AKR. We have found that the parallel electric field in the ion cyclotron wave modulates the energy density of the electrons at the ion cyclotron frequency. Forced oscillation of the parallel electric field with the ion cyclotron frequency has been added in the simulations to see the influence on AKR. The growth rate of AKR decreases significantly when the ion cyclotron wave has the parallel phase velocity in the same direction as the electron beam. We have found that the intensity of the AKR as well as the electron energy density is also modulated by the ion cyclotron wave. We will discuss how the modulation of the electron energy affects the growth of AKR and how this modulation may generate negative frequency drifting fine structure of AKR.