Spectroscopic measurements in the post-hole convolute on Sandia's Z-Machine (invited)

Pulsed power is a key driver for high energy density (HED) science. The Z-Machine is the world's largest pulsed power driver, and as such is one of the foremost platforms for HED science. The double post-hole convolute current adder is a critical element in low impedance, multi-module pulsed power device design. Post-refurbishment, the current loss in the convolute has reached as high as 5 MA (20% of the MITL current). Measurements of the plasma forming in this region will lead to a better understanding of the losses, and may help with a redesign of the system. Spectroscopic measurements of the convolute show strong continuum emission with absorption features. Most notably we observe the hydrogen H-alpha at 6563 Å. Lithium was introduced into the convolute as a tracer; this experiment put upper and lower bounds on the axial position of the observed continuum emitter, (located in the upper post-hole). Measurements of the location of continuum emission as a function of time indicate that plasma travels from cathode to anode with an apparent velocity of greater than 7 cm/μs.