A systematic study of current flow and impedance behavior in the Z machine double post-hole convolute

Sandia´s Z-Facility is used to conduct high energy density science experiments. Large pulsed power drivers, such as Z, are designed to deliver a large current with a short risetime to a magnetically-driven load. This often requires the use of multiple self-magnetically insulated transmission lines (MITL) in parallel to reduce inductance. The MITL currents must be recombined into a single anode-cathode gap at the load, often through a post-hole convolute. Efficient post-hole convolute operation is necessary to maximize the current delivered to the load. The Z machine utilizes four parallel MITLs and a double post-hole convolute. The current at several radial locations in the MITLs is inferred from B-dot monitor measurements. The MITL current downstream of the convolute can be several Mega-amperes less than the sum of the currents flowing in the MITLs upstream of the convolute. A systematic study of the convolute shunt current and convolute impedance for several types of Z experiments has been conducted. Convolute behavior is highly dependent on convolute voltage, which is a strong function of load type. Variations for nominally identical experiments are measurable, but small by comparison.