A shielded, multichannel, extreme ultraviolet spectrograph for fusion plasma diagnostics

A high throughput, shielded, multichannel, extreme ultraviolet (XUV) spectrograph to be used for plasma diagnostics was built. The instrument uses seven hollow fibers to transport the radiation by multiple grazing incidence reflections from the tokamak port through the instrument's shield to the spectrometer entrance slit. In this way, the ratio of background radiation streaming through the entrance slit to XUV flux is reduced by a factor of at least 2500. The seven hollow fibers provide seven channels corresponding to seven different lines of sight through the plasma. The spectrograph uses a toroidal mirror together with a plane, aberration-corrected grating to disperse radiation in the 50-200 Å region. Up to seven spectra are recorded simultaneously, at rates of 30-90 Hz, using a microchannel plate assembly optically coupled to a charge-coupled device camera. This will permit, during a single discharge, measurement of spatial emissivity profiles from various ionization states of an injected impurity, providing a better understanding of their time evolution and valuable information on cross-field ion transport.