Modeling gap closure within vaporizing transmission lines of pulsed power machines using particle-in-cell direct simulation Monte Carlo (PIC-DSMC)
In this thesis the applicability of two novel numerical methods - Event Splitting (ES) and Dual Grids - was studied for modeling gap closure within an overall DSMC-PIC approach. Gap closure is a difficult computational problem due to massive gradients in density and electrostatic properties, extreme regime (relativistic electrons), and highly nonequilibrium characteristics. It is very challenging this time to fully resolve the temporal and spatial grids and run a simulation to completion for a full-scale problem given these parameters due to limitations in computational resources. To approach the full problem, however, the above numerical methods were first tested on a steady-state, fully resolved problem, the Turner benchmark test case where they successfully demonstrated a decrease in computational costs and simulation noise (Turner et al., 2013). For an unresolved and unsteady simulation like gap closure, however, event splitting loses numerical stability faster than standard variable weight DSMC due to distortion of the distribution functions brought on by exponential macroparticle growth and subsequent merging. For the gap closure problem, Dual Grids offers a way to reallocate resources to resolving physics of greater interest; the collision scheme requires more resolution due to the high density highly collisional plasma layer that forms microns from the cathode surface while the electromagnetic (EM) field solve can be handled with a coarser grid.
Event splitting, Dual grids, DSMC, PIC, Gap closure, Plasma, Pulsed-power
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