PIC Simulation of Energetic-ion Injection Effects on Nonlinear Development of Lower Hybrid Wave Instabilities

By means of one-dimensional, electromagnetic, particle-in-cell simulations, we investigate the nonlinear development of lower hybrid wave (LHW) instabilities driven by energetic ions with a ring-like velocity distribution, paying special attention to the effects of energetic-ion injection. We consider the LHWs propagating perpendicular to the magnetic field in a collisionless plasma into which energetic ions with a speed smaller than the Alfven speed are continuously injected. We found that the LHWs excited by the energetic ions can maintain large amplitudes for a long time because the continuous injection causes the steep gradient of the energetic-ion velocity distribution. Furthermore, as time advances, the wavenumber of excited modes become larger. Because of this nonlinear development of the LHWs, the energy transfer from the energetic ions to bulk ions through the LHWs is enhanced. As the injection speed increases, a wide wavenumber range of the modes are excited and the bulk-ion energy change increases.