Simulation Study of High-Frequency Magnetosonic Waves Excited by Energetic Ions in Association with Ion Cyclotron Emission

Abstract

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).

RF Wave Detection with High-Frequency Magnetic Probes in LHD

“…In this data set, the perpendicular beam species was deuterium and the magnetic axis was fixed at R = 3.6 m. The absolute value of magnetic field strength on axis was between 2.705 and 2.85 T. The frequency increases with the line-averaged electron density. In order to simulate RF waves excited by energetic ions, Particle In Cell (PIC) simulation was conducted with the following assumptions [11].…”

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

“…9,10) When the energetic-ion ring speed is much smaller than the 1/20 Alfvén speed, electrostatic lower hybrid waves (LHWs) are excited. 11,12) Here, we define the LHWs as electrostatic waves around the lower hybrid resonance frequency ω LH , which is given by…”

Simulation Study of Energetic Ion Driven Instabilities near the Lower Hybrid Resonance Frequency in a Plasma with Increasing Density

“…2, the simulation code treats both the electrostatic and the electromagnetic fields by calculating the full Maxwell's equation. We pay attention to magnetic fluctuations shown in the simulation, as in the previous paper [8].…”

“…In ref. [8], we investigated the linear and nonlinear evolution of instabilities due to energetic ions produced by the perpendicular NBI, assuming that the energetic ions have a ring-like distribution in the velocity space perpendicular to the magnetic field. It was shown that in addition to electromagnetic emissions near the ion cyclotron frequency and its harmonics, the high-frequency magnetosonic waves with frequencies slightly smaller than ω LH grow to large amplitudes.…”

“…The density and the value of ω LH /Ω i are much smaller than those considered in Ref. [8]. In order to study the mechanism of the stair-like frequency chirping observed at the plasma start-up phase of the LHD experiments [7], we perform a simulation of instabilities driven by energetic ions injected continuously in a plasma with the increasing density and the increasing ω LH .…”