Engineering the Alcator C-Mod MSE diagnostic: Solutions to reactor-relevant diagnostic challenges

Deploying precise optical diagnostics in harsh reactor environments poses significant engineering challenges including limited access, large forces, time-varying systematic errors, reflections, low signal-to-background levels and a need for in-situ calibration. Fielding a polarization-based Motional Stark Effect (MSE) diagnostic on Alcator C-Mod has proven to be difficult due to similar challenges, which has led to the development of solutions that enable polarization angle measurements with an accuracy of 0.2 degrees.