High-Speed, Large Field-of-View (FOV) Schlieren Diagnostic for High-Power Plasma Jet Formation Study

High-power plasma jets are used as the first stage of sheared-flow-stabilized (SFS) Z pinches which have been identified as a promising approach to creating thermonuclear fusion [Shumlak, J. Appl. Phys. 127 (2020)]. The plasma jet introduces sheared-flow that mitigates MHD instabilities and is therefore crucial in creating long-lived, magnetically confined Z pinch plasmas. In SFS Z pinches, an MHDaccelerator is utilized to create the seed plasma jet. Effective compres sion and heating of an SFS Z pinch necessitates an understanding of the initial conditions required to produce stable plasma jets from the MPD accelerator. The initial plasma jet formation may be turbulent, causing MHD instabilities to be seeded in the plasma before the sheared-flow can stabilize the jet [Under wood et al., Sci Rep. 9, (2019)]. A high degree of spatio-temporal resolution is required to fully diagnose and characterize plasma jet formation and stability. To this end, a large field-of-view schlieren system capable of acquiring images every microsecond throughout the plasma pulse is fielded on ZaP-HD to study high-power plasma jet formation. Previously, digital holographic interferome try (DHI) was utilized for such studies, but has a limited FOV due to beam expansion limitations. Furthermore, DHI only provides a single snapshot per plasma pulse. The most challenging design aspect for schlieren is overcoming the self-emission from the plasma without the use of a laser. Implementing an LED light source expands the design space to allow for a large FOV, avoiding optical aberrations due to laser over-expansion. Design considerations, final im plementation, and initial schlieres of high-power MPD accelerator plasma jets are discussed.