  Dielectric breakdown strength is one of the critical performance metrics for
gases and mixtures used in large, high pressure gas time projection chambers.
In this paper we experimentally study dielectric breakdown strengths of several
important time projection chamber working gases and gas-phase insulators over
the pressure range 100 mbar to 10 bar, and gap sizes ranging from 0.1to 10 mm.
Gases characterized include argon, xenon, CO2, CF4, and mixtures 90-10
argon-CH4,90-10 argon-CO2and 99-1 argon-CF4. We develop a theoretical model for
high voltage breakdown based on microphysical simulations that use PyBoltz
electron swarm Monte Carlo results as input to Townsend- and Meek-like
discharge criteria. This model is shown to be highly predictive at high
pressure, out-performing traditional Paschen-Townsend and Meek-Raether models
significantly. At lower pressure-times-distance, the Townsend-like model is an
excellent description for noble gases whereas the Meek-like model provides a
highly accurate prediction for insulating gases.
