Numerical Model of the Darht-2 Accelerating Cell

The DARHT-2 facility at Los Alamos National Laboratory accelerates a nominally 2-musec, 2-kA electron beam to 18-MV using a series of inductive accelerating cells. The cell inductance is provided by large Metglas 2605SC cores, which are driven by pulse-forming networks. The original cell design was susceptible to electrical breakdown near the outer radius of the cores. We developed a numerical model for the magnetic properties of Metglas over the range of dB/dt (magnetization rate) relevant to DARHT, and implemented the model in the Lsp electromagnetic code. Lsp simulations showed that the field stress distribution across the outer radius of the cores was highly nonuniform. This was subsequently confirmed in experiments at LBNL. The calculated temporal evolution of the electric field stress inside the cores approximately matches experimental measurements. The cells have been redesigned to greatly reduce the field stresses along the outer radius, and a refurbishment program is underway.