Visualization of density structures in tokamak edge plasmas using lithium beam fluorescence

To study the local behavior of the edge plasma density in the DIII-D tokamak, we image the collisionally induced fluorescence from an injected neutral lithium beam using a gated intensified charge-coupled device (CCD) camera coupled to a UNIX workstation. The goal of these experiments is to search for spatially coherent structures in the plasma edge density which may be transiently illuminated by the beam. In our imaging studies to date we have been able to follow the evolution of the edge density as the main plasma discharge progresses through various confinement states under intense neutral beam injection (NBI) heating