The Distribution of Current in the Four Wires of a Four-Wire Z-Pinch at 0.8-1 MA Peak Current

Summary form only given. The COBRA accelerator is a pulse generator capable of producing up to 1 MA current pulses with rise times as short as 100 ns for wire-array Z-pinch experiments. The machine is driven by two 53-kJ Marx generators, each of which feeds two pulse-forming lines. All four of the lines in parallel drive the load. The purpose of this experiment is to better understand the dynamics of an array implosion by investigating the distribution of current in a simple wire array for the duration of the current pulse. To accomplish this, the anode hardware was segmented such that each load wire in the array was designated its own return current post. Thus, with sufficient inductive and capacitive isolation, measurement of the current in each of these return current posts yields the current in each load wire. The experimental goal for timing accuracy was less than 1 ns. To accomplish this, signal cables were prepared to be as close to the same length as possible and then timed using a 20-ns pulse along with a 6-GHz oscilloscope. Current measurements were made using Rogowski coils of various types and geometries. Different versions of the segmented anode hardware were tested to find the setup that would best hold off the accumulation of plasma near the anode, and hence best maintain electrical isolation between the various segments. This hold-off time was shown to be at least 17 ns in early experiments, but has recently been improved to over 100 ns. The maximum difference in the start time of current flow in one wire relative to another (i.e., the initiation delay) is shown to range from 2 ns to 17 ns. Throughout this experiment, various diameters of both tungsten and aluminum wires were used. Results focus on the magnitude and pulse shape of current in each wire, as well as the relative timing of current initiation in each wire