Development of a multichannel filterscope system for two-dimensional plasma imaging in a magnetic mirror.

We have developed a multichannel filterscope system for time-resolved two-dimensional (2D) plasma emission imaging in the KAIST magnetic mirror device. The system consists of three compact in-vessel receiver modules with slit-based pinhole-camera geometry, an optical feedthrough coupled to fiber bundles, and external silicon photomultiplier-based detection units. The receiver modules, separated by 120°, provide 21 line-integrated viewing chords across the plasma cross section. Plasma emission is spatially selected by a precision slit, collimated by lens optics, spectrally filtered by an interchangeable narrow bandpass filter, and transmitted outside the vacuum vessel through the optical feedthrough and fiber bundles. Initial measurements during helium discharges successfully exhibited simultaneous time-resolved detection of neutral helium emission near 668 nm from all 21 channels. The gain-corrected line-integrated signals were then used to reconstruct 2D emissivity distributions. The reconstructed images showed a non-axisymmetric emission structure and its temporal evolution, demonstrating the capability of the developed system for time-resolved 2D plasma emission imaging.