Development of a Multiplexed Interferometer System for the Polaris Field Reversed Configuration Prototype

Polaris, Helion Energy's seventh generation field reversed configuration (FRC) prototype has the primary goal to demonstrate direct electricity recovery from fusion. Densities in the range of 1E21 – 1E23 m-3 are expected throughout the pulsed operation of the machine. A multichannel, 1550 nm fiber-based Michelson interferometer was developed to characterize the density distribution along multiple chords of the device. Telecommunication wavelengths in the C band are combined into common transmission fiber lines using dense wavelength division multiplexing (DWDM) and amplified with Erbium-doped fiber amplifiers (EDFA). View chords are radially centered and distributed axially along the machine. Corner-cube retroreflectors are used to streamline system integration while effectively boosting signal strength due to a double pass through the plasma. Initial data from an 8-channel version of this diagnostic fielded on Helion Energy's FRC formation optimization test bed are presented.