Experimental Study on Alfvén Instability in a Magneto-Plasma Dynamic Arc-Jet Collisional Finite-β Plasma

Test plasma high-density (TPH) was a research facility that started in the 1980s, generated high-density plasma using magneto-plasma-dynamic (MPD) arc-jet, $\beta =8\times {10}^{-3}$, where $\beta$ is the ratio of the kinetic pressure divided by the magnetic field pressure. In this work, we aim to authenticate the method used in the identification of the current-driven instability in high-frequency mode as Alfvén instability, standing on the linear trend of the difference of the phase of the Fourier transforms of the magnetic field fluctuation. The dependence of the wavenumber-versus-frequency shows a linear regression, close to the Alfvén velocity expected from the plasma density, ion mass and the strength of the magnetic field. With short wave packets of the left-hand, circularly polarized Alfvén waves were recorded for the spectral analysis and reconstructed the spatial changes in the phase spectrum. The dispersion in the frequency stretch was found to be traced as the Alfvén mode. Artifacts such as standing waves affect a narrow range of phase spectra and have large leverage as an error in the linear regression analysis. The coherence spectrum for the validation and the method of recovering data using maximum likelihood estimation will be presented. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.