Stark Broadening Density Profile Measurements in the ZaP Experiment

The ZaP Flow Z-Pinch experiment uses sheared flow to mitigate MHD instabilities. The high-pressure plasma pinches exhibit Stark broadened emission spectra, which are analyzed to determine plasma density. A 20-chord spectroscopic system has been calibrated to quantify chord-to-chord variation in throughput, optical curvature effects, instrument wavelength displacement, and instrument broadening. By correcting for these effects and accounting for Doppler broadening, a Stark broadening profile can be resolved and used as a measure of plasma density. The local electric field from the plasma Stark broadens the spectral shape of line emission producing a Voigt profile. A Fourier expansion technique is used to approximate the Voigt profile for a C III spectral line, which is emitted from the center of the plasma column, and the H$_{\beta}$ line, which is used to resolve density in the peripheral regions of the plasma. By measuring density at different locations, a radial density profile is generated. This profile is then compared to interferometry measurements and is used to gain a better understanding of Z-pinch equilibrium.