Bispectral Analysis of Harmonic Oscillations Measured using Beam Emission Spectroscopy and Magnetic Probes in CHS

Abstract

The coherent MHD oscillation, which consists of the fundamental frequency of several kilohertz and its higher harmonics, (harmonic oscillation: HO) has been observed in Compact Helical System. HO consists of two pairs of harmonic series. One is located in the core region near the ι = 0.5 rational surface (denoted as "HO (core)"), the other is located in the edge region near the ι = 1.0 rational surface (denoted as "HO (edge)"). In the present study, bispectral analysis is applied to the fluctuation data, for which HO is measured by beam emission spectroscopy (BES) and using magnetic probes. The analysis has revealed that fundamental mode of HO in both the magnetic and core density fluctuations have phase correlation with the harmonics including fundamental oscillation, while HO in edge density fluctuation does not have such phase correlation. Mode numbers of HOs are identical for harmonic components having different frequencies, i.e., m/n = −2/1 for HO (core) and m/n = −1/1 for HO (edge). It suggests that the generation of harmonics cannot be interpreted simply as mode coupling because the summation rule for the wavenumber is not satisfied, even though the bicoherence value is significant. The bicoherence value and relative amplitude of higher harmonics correlate with each other, which suggests that bicoherence indicates the degree of distortion of the signals.

Effect of Boric Acid Flux and Drying Control Chemical Additive on the Characteristics of Y2O3:Eu Phosphor Particles Prepared by Spray Pyrolysis

“…-The discharges (a typical shot: 21539) were performed on EAST tokamak at circular configuration heated only by ohmic power. The reason why the circular configuration discharge was chosen is that the previous reference argued about the plasma configuration effect on the spectrums of MHD diagnostic signals [14]. The plasma small radius is a = 48 cm, and the central line-averaged density is about n e = 2.6 × 10 19 m −3 with the edge safety factor q a = 5.4.…”