Simulation study of high-frequency magnetosonic waves excited by energetic ions in association with ion cyclotron emission

Instabilities of high-frequency magnetosonic waves caused by energetic ions with a ring-like velocity distribution are studied with a one-dimensional electromagnetic particle code which simulates self-consistently the full ion and electron dynamics. It is shown that the magnetosonic waves with frequencies slightly smaller than the lower-hybrid resonance frequency rapidly grow to large amplitudes, in addition to electromagnetic emissions near the ion cyclotron frequency and its harmonics. The frequency of the magnetosonic wave that has the largest amplitude is in good agreement with the frequency of the most unstable mode predicted by a linear theory. The theory and simulations show that the frequency of the magnetosonic wave increases with the plasma density. The instability of the high-frequency magnetosonic waves may be an excitation mechanism for radio frequency waves in the Lower Hybrid Wave (LHW) frequency region observed in the Large Helical Device (LHD). (author)