The absorption profile analysis of electron cyclotron waves by three dimensional ray tracing simulation under the overdense state in the magnetospheric plasma device RT-1

In the magnetospheric plasma device RT-1, in which a superconducting ring magnet is levitated in the vacuum to produce a dipole magnetic field, the plasmas are produced by electron cyclotron heating (ECH) using 2.45 GHz. In this condition, inward diffusion causes a peaked density profile beyond the cutoff density, even though the electron density is higher than the O-mode cutoff density of 2.45 GHz EM wave. We found that the density limit appears beyond the cutoff density. Therefore, we clarify the mechanism in terms of wave physics in plasmas.

In this study, we have developed a ray trace code for the RT-1 to analyze a power deposition of EC waves and measured the profiles of electron density and electron temperature distributions necessary for the calculation from experiments.

As a result of spectroscopy, the electron temperature profile with two peaks of about 20 eV was obtained. Compared to the results of the two-dimensional calculation[Mori et al. PFR 2022], the absorption efficiency in the three-dimensional calculation model is increases when the cutoff density occurs. This is thought to be due to the effect of EM wave wraparound in three dimensions and reaching the resonance layer on the opposite side of the incident position.