Intensified imaging of PFC erosion via Mo I emission in C-mod

Understanding erosion of plasma facing components (PFCs) in high performance discharges is important for minimizing core assimilation of impurities and re-deposition onto optical surfaces. A new diagnostic at C-Mod images PFC erosion via emission from sputtered particles using an intensified charge injection device camera. The system is absolutely calibrated to enable measurement of erosion fluxes. Continuum emission, which enters the camera in addition to the desired Mo I line emission, must be subtracted from the camera image before interpreting the eroded flux. A visible spectrometer with views coincident to the camera is used to separate the continuum and line emission sources in some circumstances, but this technique is only effective when all continuum sources are toroidally symmetric. Localized continuum sources including Planck emission and deuterium molecular emission complicate interpretation. A more robust system is described which is capable of subtracting such localized continuum sources by simultaneously imaging line emission and a spectrally adjacent continuum region. Initial results are also presented comparing C-Mod operation during startup, lower hybrid current drive, ion cyclotron heating, before and after boronization, and various modes of confinement.