Edge Density Imaging Measurements of DIII-D Tokamak Plasmas using a Lithium Beam Probe and High Resolution Camera

The Lithium Atomic Beam (LIBEAM) used on DIII-D has shown considerable potential to diagnose the density profile $n_e(r)$ with a radial resolution of $\Delta r = 0.5$~cm within the pedestal region. The LIBEAM parameters are $E < 30$~keV and $\sim$10 mA of equivalent neutral lithium current. Through the use of a filtered high resolution PCO Pixelfly CCD camera, the spectroscopic emission of the 670.8 nm Li[2p$-$2s] transition due to collisional excitation of the neutral lithium atoms is captured and analyzed. By appropriate image analysis, a high resolution profile of the beam intensity $I_b$ can be discerned. Through the use of this beam intensity profile and collisional radiative models (CRM) the fine scale structure of the edge density profile $n_e(r)$ can be observed.