A High Temporal and Spatial Resolution Electron Density Diagnostic Based on Stark Broadening

Passive spectroscopic measurements of Stark broadening have been reliably used to determine electron density for decades. However, a low-density limit (~10 13 cm −3 ) exists due to Doppler and instrument broadening of the spectral line profile. A synthetic diagnostic for measuring electron density capable of high temporal (ms) and spatial (mm) resolution is currently under development at Oak Ridge National Laboratory. The diagnostic is based on measuring the Stark broadened, Doppler-free, spectral line profile of a Balmar series transition using an active laser based technique. The diagnostic approach outlined here greatly reduces both of these broadening contributions using Doppler-free saturation spectroscopy (DFSS), allowing access to lower density regimes than previously realized.