Pulsed power performance of the Z machine: Ten years after the upgrade

The Z machine is a 36-module, multi-megavolt, low impedance magnetic pressure driver for high-energy-density physics experiments. In 2007, a major re-build doubled the stored energy and increased the peak current capability of Z. The upgraded system routinely drives 27 MA through low inductance dynamic loads with 110 nanosecond time to peak current. The Z pulsed power system is expected to be prepared for a full-energy experiment every day, with a small (<2%) chance of pulsed power system failure, and ±2 ns timing precision. To maintain that schedule with 20 MJ stored, it becomes essential to minimize failures that can damage hardware. We will show the results of several improvements made to the system that reduce spurious breakdowns and improve precision. In most cases, controlling electric fields is key, both to reliable insulation and to precision switching. The upgraded Z pulsed power system was originally intended to operate with 5 MV peak voltage in the pulse-forming section. Recent operation has been above 6 MV. Critical items in the pulsed power system are the DC-charged Marx generators, oil-water barriers, laser-triggered gas switches, and the vacuum insulator. We will show major improvements to the laser-triggered gas switches, and the water-insulated pulse forming lines, as well as delivered current reproducibility results from user experiments on the machine.