1D and 2D circuit-code modeling of the refurbished Z accelerator

Now that the refurbishment of the Z machine at Sandia is complete we are routinely operating with currents over 26 MA into various loads. With routine operation we are able to measure current and voltage throughout the machine and compare with circuit code predictions. These measurements have motivated improvements to the original model to include two-dimensional (2D) and three-dimensional (3D) sub-circuits. In this paper we describe a full-machine (36 module), one-dimensional (1D) circuit model of Z using the Bertha code developed at the Naval Research Laboratory. We also describe a model that uses 2D sub-modules. In addition, we discuss plans for implementing a 3D circuit model to allow investigating azimuthal effects that can be important for tailoring the rise time, shape, and length of the Z output pulse. Pulse tailoring on Z is achieved by staggering the timing of the various pulsed-forming modules, and by operating individual modules in either long or short-pulse modes. Since the individual lines combine at a large diameter and are separated azimuthally, transit-time effects can be important for determining transient field enhancements at the vacuum insulator and in the vacuum transmission lines, as well as pulse shape. Finally, we compare the 1D and 2D models with data, and provide predictions for both short and long pulse modes for various load configurations.