Development of a Thomson Scattering Diagnostic on a Pulsed Power Machine and its use in Studying Laboratory Plasma Jets Focusing on the Effect of Current Polarity

176 pagesThis research primarily focused on the development of a collective Thomson scattering system for experiments on a 1~MA 100~ns pulsed power generator at Cornell University (COBRA). This diagnostic is capable of determining, at a minimum, the electron temperature, electron density and the flow velocity in the plasma. It was used in experiments on plasma jets created using a radial Al foil (thin disk of foil) load on COBRA. These jets served as a good load as they were long-lasting and at the center of the experimental chamber. The first set of experiments explored the rotation of the jet when an external magnetic field is applied and found the jet to be rotating at about 20~km/s. During these experiments, it was discovered that the Thomson scatter laser energy (10~J) was sufficient to heat the 20~eV jet plasma by inverse bremsstrahlung. While this did not affect the velocity measurements, it did significantly affect the measured temperature of the plasma. To better study this perturbation, a streak camera was set up to measure the changing temperature during the laser pulse. The plasma was found to be heated from about 20 to 80~eV in the first half of the laser pulse, before cooling down due to the expansion of the plasma. We also started developing a system to record the high-frequency Thomson scattering spectral feature to measure the density of the plasma. This showed some initial promising results and suggested densities of at least $5\times10^{18}$~cm$^{-3}$. Finally, using low enough laser energy to avoid laser heating of the plasma, the effect of current polarity on the plasma jets was studied experimentally. It was found that while jets with a radial outward current flow were denser and wider than jets with a radial inward current, both jets had a similar electron temperature. These experiments were also compared to extended magnetohydrodynamic (XMHD) simulations. While experimental jets had about the same width as those in the simulation, they were found to be slightly colder and significantly less dense than the simulations