Upgraded Collective Thomson Scattering for the Sheared-Flow-Stabilized Z Pinch*

Zap Energy is undertaking a number of upgrades to the Thomson scattering diagnostic used on the FuZE and FuZE-Q sheared-flow-stabilized (SFS) Z-pinch devices to measure the temperature, density and flow velocity profiles of the plasma. These measurements are fundamental to understanding the SFS Z-pinch fusion reactor concept, including determining the scientific fusion gain, Q, of the devices. The previous diagnostic used an 8-J, 532-nm q-switched Nd:YAG laser and a single intensified CMOS-based spectrometer to study collective Thomson scattering spectra. The system measured both electron plasma wave (EPW) and ion acoustic wave (IAW) components of the spectra. Analysis of these spectra yield multi-keV electron temperatures, densities on the order of 10²³ m^-3 and velocities in 100s of km/s across a 17-point spatial profile. Ongoing upgrades include expanding the laser setup to include multiple, double-pulsed lasers to allow for additional time measurements and expanding the spectrometer arrangement for simultaneous EPW and IAW measurements. Further plans include variable zoom collection optics and sharing the diagnostic between multiple devices. A Bayesian framework provided multi-parameter fitting and error analysis of the spectra, accounting for the noise characteristics of the image intensifier.