High-sensitivity measurement of Zeeman effect using hydrogen Paschen-α emission line in fusion-divertor-relevant plasma

Abstract

In magnetically confined fusion reactors, the Zeeman effect can sometimes be utilized in spatially resolved spectroscopy to localize the observed line emission. To apply this method to divertor plasma spectroscopy, the relative magnitude of the Zeeman splitting to linewidth for hydrogen atomic emission lines in the visible to the near-infrared range was evaluated. It was found that the magnitude becomes the largest for the Paschen-α (Paα) emission line (1875 nm, 3-4). The observability of the Zeeman splitting on the Paα emission line spectrum was confirmed by an experiment using a hydrogen pellet ablation plasma in Heliotron J, which is relevant to the divertor plasma in terms of magnetic field strength (1.2 T), electron temperature (∼1 eV), and electron density (3.6 × 1020 m-3).