Simultaneous observations of temporally and spatially resolved two-dimensional profiles of ion-confining potentials and ion fluxes using novel ion-energy spectrometer arrays

Abstract

Newly designed spectrometer arrays for ion-energy-spectrum observations are proposed and constructed in both end regions of the GAMMA 10 tandem mirror so as to obtain two dimensionally resolved radial profiles of end-loss-ion fluxes IELA, ion temperatures, and ion-confining potentials φc by the use of a single plasma discharge alone. Each spectrometer unit in the array has a specific structure with obliquely placed multiple grids with respect to the direction of the ambient plasma-confining magnetic fields. This structure is proposed to obtain precise ion-energy spectra without the disturbance of simultaneously incident energetic electrons into the array, since widely distributed “multigridded Faraday cup” signals have significant electron disturbances on ion spectra even if over a few tens of kV are applied to the electron-repeller grid. In tandem-mirror experiments, plasma-confining potentials produced by electron cyclotron heatings play one of the most critical roles in the improvement of simple-mirror confinement. Thus, diagnostics of these confining potentials using clear ion spectra are of essential importance. From these motivations, the spatial distribution details and relations of φc and IELA are investigated by the use of the novel ion spectrometers. Axisymmetric profiles of φc are found to have a good correlation with axisymmetric plugging distributions in IELA. These are consistently interpreted in terms of the Pastukhov theory of the relation of φc with IELA. Information on such specific spectrometer arrays would contribute to researchers in a wide variety of plasma devices, who employ analyzers for flux, temperature, and potential diagnostics under energetic plasma circumstances.