Development of lithium beam emission spectroscopy as an edge fluctuation diagnostic for DIII‐D (invited)
As part of the DIII‐D diagnostic complement designed to address L–H transition physics issues, we have developed and commissioned a diagnostic neutral lithium beam and multichannel fluorescence detection system to investigate the edge plasma density and its associated fluctuations. The use of lithium offers several advantages for tokamak edge beam emission spectroscopy studies, including large excitation cross sections which are relatively insensitive to temperature variation, the availability of the 670.8 nm resonance line well separated from most plasma line emission, and the suitability of modest beam energies and currents to probe even dense H‐mode plasmas. These features permit measurements of collisionally induced fluctuations to be obtained with good spatial (≪1 cm) and temporal (≪10 μs) resolution. The improvements over previous lithium beam diagnostics which were required to successfully make these measurements in a large, remotely controlled machine environment will be discussed, along with the present state of the diagnostic system and our plans for future improvements of this technique. © 1995 American Institute of Physics.