Two basic challenges limiting the simulation capabilities of the streamer discharge community are the efficient resolution of Poisson's equation and the proper treatment of photoionization. This paper addresses both of these challenges, beginning with a graphics processing unit executed multigrid (MG) algorithm to efficiently solve Poisson's equation on a massively parallel platform. When utilized in a 3D particle-in-cell (PIC) model with radiation transport, the MG solver is demonstrated to reduce the required simulation time by approximately a factor of three over a conventional Jacobi scheme. Next, a fully theoretical photoionization model, based on the basic properties of N 2 and O 2 molecules is developed as an alternative to widely utilized semi-empirical models. Following a review of N 2 emission properties, a total of eight transitions from only three excited states are reported as a base set of transitions for a practical physicsbased photoionization model. A 3D PIC simulation of streamer formation is demonstrated with two dominant transitions included in the radiation transport model.

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This paper details the design, simulation, and optimization of a low-impedance high repetition rate magnetically insulated transmission line oscillator (MILO) driven by a compact Marx generator. The project goals require the MILO to generate an radio frequency (RF) pulse within the S-band frequency range with a peak output power greater than 1 GW with greater than 10% efficiency. Its design is based on a set of base equation which provide critical component dimensions applied to a three-dimensional model constructed within CST studio suite used in a particle-in-cell (PIC) simulation. Additional to the geometric model, simulation of the MILO with non-ideal material properties and a lumped element modeling of the Marx generator were performed. The results of these simulations then informed changes to the model as to the optimizing performance of the device. Within the framework of the model, the final MILO design achieves the design goals with an approximate RF peak power of 4.5 GW at 2.5 GHz operating in the TM 01 mode when an input driving pulse with a peak voltage of 600 kV while providing 58 kA is applied.

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