Development of a Zeff diagnostic using visible and near-infrared bremsstrahlung light for the C-2W field-reversed configuration plasma

In C-2W, an elevated impurity concentration can lead to significant degradation of plasma performance and energy losses through radiation. To gauge plasma contamination from impurities, the effective ion charge (Zeff) can be determined from measurements of bremsstrahlung continuum radiation over a small spectral range free from line radiation. To this end, a diagnostic system including visible and near-infrared bremsstrahlung detectors was deployed in C-2W to measure time-dependent radial distributions of Zeff. The system is complemented by an array of survey spectrometers which enable full-range spectroscopic measurements of impurity emission lines from the vacuum ultraviolet to the near infrared, providing a good picture of the plasma composition. Here, the design scheme for this integrated diagnostic system is presented and discussed.