Three-dimensional PIC simulations and analysis of the operating characteristics of the three cell RITS

Abstract

Summary form only given. The Radiographic Integrated Test Stand (RITS) is the next generation, inductive voltage adder accelerator being developed at Sandia National Laboratories for driving high brightness flash radiographic sources./spl I.bar/70 ns width, 1.35 MV, 8 Ohm pulses are generated in parallel water dielectric pulse forming lines and are added in series with induction cells to form a single high voltage drive pulse. Each induction cell has a single point feed with a tapered azimuthal transmission line which uniformly distributes the incoming pulse around the bore of the cell. The individual cells are joined in series by a vacuum coaxial Magnetically Insulated Transmission Line (MITL). The accelerator can be operated in either polarity and the first three induction cells (of an eventual 12 cells) have been assembled and tested with detailed current and voltage measurements. These measurements provide a first ever detailed analysis of three dimensional behavior in single feed IVAs and offer unique data for comparison to PIC simulations. Fully three-dimensional particle in cell (PIC) simulations with the LSP code of the three cavity system are presented and compared to experimental measurements. Initial results from simulation and experiment on a single cell suggest the presence of large amplitude asymmetric modes. These modes, also present in the multi-cell system, can perturb the electron flow in the MITL, causing loss of magnetic insulation and current. Simple hardware modifications dramatically reduce the presence of such modes resulting in more efficient operation of the accelerator.