Near-infrared Bremsstrahlung radiation measurements in an advanced beam-driven FRC plasma

In magnetically confined fusion plasmas, the effective ionic charge ($Z_{eff})$ is a measure of plasma impurity content. Knowledge of $Z_{eff}$ profiles is critical since impurities can account for substantial radiative power losses. One method to determine $Z_{eff}$ is to measure the Bremsstrahlung continuum over a small spectral range free from line radiation. In TAE's C-2 and C-2U machines, impurities in apparently line-free regions near 523 nm overwhelmed the expected Bremsstrahlung signals and resulted in overestimated values of $Z_{eff}$. The near-infrared region is less affected by impurities and better suited for accurate Bremsstrahlung continuum measurements. For C-2W, an upgraded diagnostic system will be deployed to measure Bremsstrahlung signals near 1000 nm. The near-infrared system uses a suite of silicon avalanche photodetectors paired with a D$_{\mathrm{\alpha }}$ system to remove contributions from neutrals and attain improved $Z_{eff}$ estimates. A design scheme for measurements in an FRC at multiple lines-of-sight is presented and discussed.